Jeanne FREUDIGER-BONZON

Archaeometrical study
(petrography, mineralogy and chemistry)
of Neolithic Ceramics from Arbon Bleiche 3
(Canton of Thurgau, Switzerland).

<figure><img src="image_1.png" /></figure>
Département des Géosciences, Minéralogie & Pétrographie

Université de Fribourg (Suisse)

# Archaeometrical study

(petrography, mineralogy and chemistry)

of Neolithic Ceramics from Arbon Bleiche 3

(Canton of Thurgau, Switzerland).

THÈSE

Présentée à la Faculté des Sciences de l'Université de Fribourg (Suisse)
pour l'obtention du grade de *Doctor Rerum Naturalium*

Jeanne FREUDIGER-BONZON

De Lausanne, Niederbipp et Ormont-Dessous (Suisse)

Thèse n°1471

2005

Multiprint SA, Fribourg, 2005
Acceptée par la Faculté des Sciences de l'Université de Fribourg (Suisse) sur la proposition de:

Prof. Andreas Strasser, Université de Fribourg (CH), président du jury

Prof. Marino Maggetti, Université de Fribourg (CH), directeur de thèse

Prof. Robert Heimann, Technische Universität Bergakademie Freiberg (D), co-rapporteur

Dr. Vincent Serneels, Université de Fribourg (CH), co-rapporteur

Fribourg, le 04 mars 2005,

Le Directeur de thèse

Le Doyen

Prof. M. Maggetti

Prof. M. Celio
DÉDICACÉ

À ceux qui vivent, passionnément
À Jo
À Séb
Que la vie vous soit douce

À Ganj'
À Pj
À ceux qui sont partis trop tôt

"Je voudrais être un arbre, boire l'eau des orages
Me nourrir de la terre, être ami des oiseaux
Et puis avoir la tête si haut dans les nuages
Qu'aucun homme ne puisse y planter un drapeau
Je voudrais être un arbre et plonger mes racines
Au coeur de cette Terre que j'aime tellement
Et que ce putain d'homme chaque jour assassine
Je voudrais le silence, enfin, et puis le vent"

Renaud
# TABLE OF CONTENTS

ABSTRACT 10

RÉSUMÉ 11

1 - GENERAL INTRODUCTION 13

1.1 Foreword 13

1.2 The study of ceramic in archaeometry 13

1.3 Aim of the study 13

2 - A NEOLITHIC VILLAGE IN SWITZERLAND: DESCRIPTION AND HISTORY OF ARBON BLEICHE 3 15

2.1 Generalities on the Neolithic period 15

2.2 The Neolithic cultures in Switzerland 18

2.2.1 Western Switzerland 18

2.2.2 Central and eastern Switzerland 18

2.2.3 Life during the mid-Neolithic period 19

2.3 Presentation of Arbon Bleiche 3 22

2.3.1 Geography 22

2.3.2 Geology 22

2.3.3 Dendrochronology 23

3 - THE NEOLITHIC CERAMICS IN ARCHAOMETRY: STATE OF THE ART AND DEFINITIONS 25

3.1 Introduction 25

3.2 Composition of the clay 25

3.2.1 Clay 25

3.2.2 Temper 25

3.2.3 Discussion 26

3.3 Processing the clay 26

3.3.1 Forming techniques 26

3.3.2 Surface treatment 28

3.4 Firing 29

3.4.1 Firing techniques 29

3.4.2 Firing Atmosphere 31

3.4.3 Experimental firing of clays 31

3.4.4 Generalities on colour changes in the ceramic during open firings 31

3.4.5 Mineralogical transformations during experimental firings 32
<table><tr><td>3.4.5.1 Introduction</td><td>32</td></tr><tr><td>3.4.5.2 Problem of pressure and of thermodynamically incompatible minerals</td><td>32</td></tr><tr><td>3.4.5.3 Lime popping</td><td>33</td></tr><tr><td>3.4.5.4 Oxidising firing of carbonate-rich clays</td><td>33</td></tr><tr><td>3.4.5.5 Oxidising firing of silicate-rich clays</td><td>34</td></tr><tr><td>3.4.5.6 Reducing firing of carbonate-rich clays</td><td>36</td></tr><tr><td>3.4.5.7 Reducing firing of silicate-rich clays</td><td>36</td></tr></table>

<table><tr><td>3.4.6 Firing temperatures: main results of previous studies on Swiss Neolithic ceramics</td><td>36</td></tr></table>

<table><tr><td>3.4.7 Discussion</td><td>37</td></tr></table>

## 3.5 Contamination by use and burial 37

<table><tr><td>3.5.1 Introduction</td><td>37</td></tr></table>

<table><tr><td>3.5.2 Secondary montmorillonitisation</td><td>37</td></tr></table>

<table><tr><td>3.5.3 Phosphorus</td><td>37</td></tr></table>

<table><tr><td>3.5.4 Others</td><td>38</td></tr></table>

<table><tr><td>3.5.5 Discussion</td><td>38</td></tr></table>

# 4 - GENERALITIES CONCERNING THIS ARCHAOMETRICAL STUDY 39

## 4.1 Sampling Strategy 39

<table><tr><td>4.1.1 Non-ceramic material from Arbon Bleiche 3</td><td>39</td></tr></table>

<table><tr><td>4.1.2 Clays and rocks</td><td>39</td></tr></table>

<table><tr><td>4.1.3 Ceramics from Arbon Bleiche 3</td><td>39</td></tr></table>

<table><tr><td>4.1.4 Ceramics from the western Carpathian Basin</td><td>39</td></tr></table>

## 4.2 Methodology 40

<table><tr><td>4.2.1 Ceramics and non-ceramic material</td><td>40</td></tr></table>

<table><tr><td>4.2.1.1 Thin sections</td><td>40</td></tr></table>

<table><tr><td>4.2.1.2 Qualitative study of the thin sections</td><td>40</td></tr></table>

<table><tr><td>4.2.1.3 Quantitative study of the thin sections</td><td>40</td></tr></table>

<table><tr><td>4.2.1.4 X-ray diffraction</td><td>41</td></tr></table>

<table><tr><td>4.2.1.5 X-ray fluorescence</td><td>41</td></tr></table>

<table><tr><td>4.2.1.6 Statistics</td><td>41</td></tr></table>

<table><tr><td>4.2.1.7 FeO</td><td>42</td></tr></table>

<table><tr><td>4.2.1.8 CO₂ and H₂O</td><td>42</td></tr></table>

<table><tr><td>4.2.1.9 Scanning electron microscope</td><td>42</td></tr></table>

<table><tr><td>4.2.1.10 Electron microprobe</td><td>42</td></tr></table>

<table><tr><td>4.2.1.11 Nota Bene</td><td>42</td></tr></table>

<table><tr><td>4.2.2 Clays</td><td>42</td></tr></table>

<table><tr><td>4.2.2.1 Briquettes and thin sections</td><td>42</td></tr></table>

<table><tr><td>4.2.2.2 Granulometry</td><td>42</td></tr></table>

<table><tr><td>4.2.2.3 X-ray diffraction</td><td>43</td></tr></table>

<table><tr><td>4.2.2.4 X-ray fluorescence</td><td>43</td></tr></table>
**4.3 Terminology** 43

4.3.1 Non-ceramic material 43

4.3.2 Ceramics and potteries 43

4.3.3 Matrix, non-plastic or natural inclusions and temper 43

4.3.3.1 *Matrix typology* 43

4.3.3.2 *Temper typology* 44

4.3.4 Reference groups 44

**4.4 Representativeness of the data** 44

**5 - ARCHAOMETRICAL RESULTS CONCERNING THE NON-CERAMIC MATERIAL: THE 12 SAMPLES OF LOOM WEIGHT AND COB FRAGMENTS FROM ARBON BLEICHE 3** 47

**5.1 Macroscopic description** 47

**5.2 Petrographical study** 47

**5.3 Mineralogical study** 47

**5.4 Firing?** 47

**5.5 Chemical description** 47

**6 - ARCHAOMETRICAL RESULTS CONCERNING THE CERAMIC MATERIAL: THE 163 SAMPLES OF POTTERIES AND SPINDLE WHORLS FROM ARBON BLEICHE 3** 53

**6.1 Typological classification of the pottery and its relation with the Neolithic cultures from the lake Constance to the western Carpathian Basin** 53

6.1.1 Pfyn / Horgen pots related to the Pfyn and Horgen cultures 53

6.1.2 Special forms Pfyn related to the Pfyn Culture 55

6.1.3 Special forms Bayern related to the Altheim and Cham cultures from Bavaria 55

6.1.4 Special forms Boleráz related to the Boleráz stage of the Baden culture 55

6.1.5 Undetermined special forms 56

**6.2 Macroscopic Description** 56

6.2.1 Pfyn / Horgen pots 56

6.2.2 Special forms Pfyn and special forms Bayern 56

6.2.3 Special forms Boleráz 56

6.2.4 Undetermined special forms 56

6.2.5 Spindle whorls 56
## 6.3 Petrographical study 57

6.3.1 Introduction 57

6.3.2 Inclusion-poor and silicate-rich matrix: petrographical groups AI-AVI 57

6.3.2.1 Petrographical group AI: granite temper 57

6.3.2.2 Petrographical group AII: rhyolite temper 57

6.3.2.3 Petrographical group AIII: chert temper 57

6.3.2.4 Petrographical group AIV: gabbro temper 57

6.3.2.5 Petrographical group AV: grog temper 57

6.3.2.6 Petrographical group AVI: bone temper 58

6.3.3 Inclusion-rich and silicate-rich matrix: petrographical groups BI and BII 58

6.3.3.1 Petrographical group BI: granite temper 58

6.3.3.2 Petrographical group BII: grog temper 59

6.3.4 Inclusion-rich and carbonate-rich matrix: petrographical groups CI and CII 59

6.3.4.1 Petrographical group CI: granite temper 59

6.3.4.2 Petrographical group CII: grog temper 59

## 6.4 Specific studies on bone tempered ceramics 59

6.4.1 Introduction 59

6.4.2 Firing 59

6.4.3 Scanning electron microscope (SEM) 60

6.4.4 Chemical study 60

6.4.5 Microprobe 60

## 6.5 Firing of the potteries and spindle whorls from Arbon Bleiche 3 62

6.5.1 Firing process 62

6.5.2 Firing atmosphere 62

6.5.3 Mineralogical transformations during firing 63

6.5.3.1 Nota Bene 63

6.5.3.2 Experimental oxidising firing of a carbonate-rich clay
from the surroundings of Arbon 63

6.5.3.3 Experimental oxidising firing of a silicate-rich clay
from the surroundings of Arbon 64

6.5.4 Mineralogy and estimation of the firing temperatures 64

## 6.6 Chemical study 66

6.6.1 Contaminated ceramics 66

6.6.2 Statistical treatment of the data 67

6.6.2.1 Introduction 67

6.6.2.2 Descriptive statistics 67

6.6.2.3 Cluster analysis 69

6.6.2.4 Principal component analysis (PCA) 71

6.6.2.5 Mahalanobis distance (MD) 77

6.6.2.6 Exceptions 77

## 6.7 Reference groups 80

6.7.1 Arbon Bleiche 3 – a new reference group 80

6.7.2 Swiss Neolithic chemical reference groups versus Arbon Bleiche 3 ceramics 80

## 6.8 Spatial repartition 83
7 - ARCHAOMETRICAL RESULTS CONCERNING THE CERAMIC
MATERIAL: THE 14 SAMPLES OF POTTERIES

FROM THE WESTERN CARPATHIAN BASIN 85

7.1 Introduction 85

7.2 Macroscopic description 85

7.3 Petrographical study 85

7.4 Chemical description 85

8 - ARCHAOMETRICAL RESULTS CONCERNING THE POTENTIAL
TEMPER AND CLAY RESSOURCES OF THE NEOLITHIC VILLAGE

8.1 The rocks 89

8.2 The local clays 90

8.2.1 Description of the CaO-rich clays 90

8.2.2 Description of the CaO-poor clays 91

8.2.3 Interpretation 93

9 - FINAL CONCLUSIONS

9.1 Compositional discrepancy between
the non-ceramic and the ceramic material 95

9.2 Ceramics: petrographical diversity vs. chemical homogeneity 95

9.3 Observation of the first bone tempered Swiss Neolithic ceramics 96

9.4 Definition of the two traditions present in Arbon Bleiche 3 97

9.5 Firing technique, atmosphere and temperature 97

9.6 No evidence of a domestic ceramic production in Arbon Bleiche 3 97

10 - PERSPECTIVES & ACKNOWLEDGEMENT

10.1 Mineralogical transformations during firing 99

10.2 Study of the manufacturing techniques 99

10.3 Provenance of bone tempered ceramics 99

10.4 Acknowledgement 99

11 - BIBLIOGRAPHY

101
<table><tr><td>1 - APPENDIX 1</td><td>112</td></tr><tr><td>2 - APPENDIX 2</td><td>124</td></tr><tr><td>3 - APPENDIX 3</td><td>128</td></tr><tr><td>4 - APPENDIX 4</td><td>132</td></tr><tr><td>5 - APPENDIX 5</td><td>134</td></tr><tr><td>6 - APPENDIX 6</td><td>144</td></tr><tr><td>7 - APPENDIX 7</td><td>148</td></tr><tr><td>8 - APPENDIX 8</td><td>156</td></tr><tr><td>9 - APPENDIX 9</td><td>170</td></tr><tr><td>10 - APPENDIX 10</td><td>176</td></tr><tr><td>11 - APPENDIX 11</td><td>178</td></tr><tr><td>CURRICULUM VITAE</td><td>183</td></tr></table>
ABSTRACT

This PhD thesis focuses on the findings from Arbon-Bleiche 3, a Neolithic lacustrine village on the Southern shore of Lake Constance (Bodensee, Switzerland). From 1993 to 1995, 1100 m² were excavated by the archaeological service of Thurgau (LEUZINGER, 2000). The settlement was occupied during a very short period, fifteen years (3384-3370 BC) in the transitional period between Pfyn (3900-3600 BC) and Horgen (3200-2800 BC) cultures.

Dr. A. De Capitani studied the ceramics from Arbon-Bleiche 3. She observed in the ceramics several characteristics of Pfyn culture and of Horgen tradition.

She made a typological classification of the ceram-
ics separating Pfyn / Horgen pots from diverse kinds of
special forms divided into four sub-groups: special
forms Pfyn, special forms Bayern, special forms
Boleráz and undetermined special forms. Special forms
Pfyn have characteristics from the Pfyn culture, special
forms Bayern have specificities in relation with Altheim
and Cham cultures in Bavaria, and special forms
Boleráz were related to the Boleráz stage of the Baden
culture (western Carpathian Basin). For DE CAPITANI
(2002), Pfyn / Horgen pots and special forms Pfyn were
probably local. A research to detect a possible travel of
the other special forms across Europe had to be made.
This is the principal goal of this study.

First, petrographical analyses permitted to separate
non-ceramic material (cob fragments and loom weight)
from the ceramics and spindle whorls. The first group
was made of an inclusion-rich and carbonate-rich clay,
without temper for the cobs and with organic temper
for the loom weight. Inversely, the ceramics were
manufactured with an inclusion-poor and silicate-rich
clay and tempered in various ways. The ceramics were
then separated into ten petrographical group according

to the clay used and the main temper added (i.e. gran-
ite, gabbro, chert, rhyolite, grog and bone). These
groups were not in direct relation with the typological
groups of DE CAPITANI (2002).

Second, chemical analyses let three main groups separate: non-ceramic material (CaO-rich) vs. bone tempered ceramics (P₂O₅-rich) vs. the great majority of the ceramics from Arbon Bleiche 3. From an archaeological point of view, the Pfyn / Horgen pots are thought to be local. Moreover, because the ceramics cannot be chemically split into groups, the same provenance for the other ceramics is also proposed. Only 13 samples are outliers and were surely foreign. However, a study of 14 ceramics from the western Carpathian Basin (probable import area defined by the archaeologists) did not match the chemistry of the outliers (except maybe one). Their provenance was, hence, not elucidated. Only their typological features are bound to Bavaria or to the western Carpathian Basin.
# RÉSUMÉ

Le but de ce travail de doctorat a été d'étudier en détail les objets archéologiques mis à jour sur le site lacustre de Arbon Bleiche 3, village néolithique situé sur la rive Sud du lac de Constance (Suisse). Entre 1993 et 1995, le service archéologique du canton de Thurgovie a fouillé un périmètre de 1100 m² (LEUZINGER, 2000). La particularité de ce village est d'avoir été occupé pendant une très courte période (15 ans, entre 3384 et 3370 av. J.-C.), durant la période chronologique qui sépare la culture de Pfyn (3900-3600 av. J.-C.) de celle de Horgen (3200-2800 av. J.-C.), période assez mal documentée en Suisse.

La Dr. A. De Capitani a étudié le matériel céramique du site. Elle y observe des caractères des traditions Pfyn et Horgen.

Les céramiques sont classées d'après leur affinités typologiques: les pots à caractéristiques Pfyn / Horgen sont séparés des formes spéciales, divisées en quatre sous-groupes: formes spéciales Pfyn (caractéristiques de la culture de Pfyn), formes spéciales Bayern (en relation avec les cultures de Altheim et Cham de Bavière), formes spéciales Boleráz (liées à l'étage Boleráz de la culture de Baden dans la partie ouest du Bassin des Carpates) et les formes spéciales indéterminées. DE CAPITANI (2002) propose une origine locale pour les pots Pfyn / Horgen et pour les formes spéciales Pfyn. Un import de céramiques depuis l'Allemagne ou le Bassin des Carpathes étant probable, le but de ce doctorat est d'affirmer ou d'infirmer cette hypothèse.

Les analyses pétrographiques ont tout d'abord permis de séparer le matériel non céramique (torchis et poids de tisserand) des céramiques et des fusaïoles. Le premier groupe est fait d'une argile riche en inclusions et carbonatée ; le torchis n'étant pas dégraissé, contrai-

rement au poids de tisserand (dégraissé par de la matière organique). Les céramiques, en revanche, sont formées d'une argile siliceuse contenant peu d'inclusions et sont dégraissées.

Les céramiques ont ensuite été séparées en 10 groupes pétrographiques différents, en fonction de leur argile et de leur plus important dégraissant (grande, gabbro, rhyolite, chert, chamotte ou os). Ces groupes n'ont pas de relation directe avec les groupes typologiques.

Les analyses chimiques, quant à elles, ont permis de séparer trois groupes principaux : le matériel non céramique (riche en CaO), les céramiques dégraissées à l'os (riches en P₂O₅) de la grande majorité des céramiques d'Arbon Bleiche 3. Du point de vue archéologique, les pots Pfyn / Horgen sont locaux. La majorité des céramiques ne pouvant pas être séparées chimiquement, nous pensons qu'elles ont aussi été produites localement. Seuls 13 échantillons sont des exceptions ; ils ne sont donc pas locaux. Malheureusement, leur chimisme ne correspond pas à celui des céramiques du bassin ouest des Carpathes, lieu de production supposé (exception peut-être de un échantillon). Leur provenance n'a donc pas pu être élucidée. Seules les caractéristiques typologiques des céramiques de Arbon Bleiche 3 ont un lien avec la Bavière ou le bassin des Carpathes.
<figure><img src="image_2.png" /></figure>
# 1 - GENERAL INTRODUCTION

## 1.1 FOREWORD

The Arbon Bleiche 3 project is the result of three distinct phases. First, excavations were made between 1993 and 1995 under the direction of the archaeological service of Canton Thurgau, J. Bürgi and U. Leuzinger. A first synthesis was published, describing the excavated area (geography, stratigraphy and map of the site). Every Neolithic house is presented, together with the archaeological findings (LEUZINGER, 2000).

Second, an interdisciplinary team of archaeologists and biologists was created to study the material brought to light, i.e. stones, woods, textiles, ceramics and bones (DE CAPITANI ET AL., 2002).

This PhD, focusing on the archaeometrical study of the ceramic products of Arbon Bleiche 3 is part of specialised studies of natural sciences and was financially supported by the Swiss National Science Foundation (Project 12-52498.97), and done from 1999 to 2005 at the University of Fribourg, Department of Geosciences, under the direction of Prof. M. Maggetti.

Three articles in direct relation with this work are in press (BONZON, 2003, 2004A, 2004B) and one will be proposed soon (BONZON-FREUDIGER, 2005). The first one deals with the petrographical and mineralogical study, the second one summarises this work, the third one presents the bone tempered ceramics and the last one will discuss the representativeness of archaeometrical analyses (Appendix 12).

## 1.2 THE STUDY OF CERAMIC IN ARCHAOMETRY

A ceramic is a marker that helps archaeologists to identify cultural groups. The study of the ceramic materials, the nature of its compounds and the way it was manufactured by the potter will lead to a better understanding of the ceramic production of the Past. These kinds of studies are part of archaeometrical researches. In this study, petrographical, mineralogical and chemical analyses will be used to describe archaeological material.

A great abundance of broken ceramic sherds may cause problems to archaeologists: a satisfactory identification by stylistic criteria like colour and shape is not always possible because sherds are too similar or because not enough of these correspond to reconstruct the ceramics. Hence, some very interesting questions, such as “What technique was used to produce this ceramic?”, “Where was it made?” and “How did it get here?” can only be partially answered by archaeologists. A precise study of the material composing the ceramics often may answer such questions. The aim of researches in archaeometry is, for example, to determine the origin of each component of one ceramic; the reason why the potter chose this kind of material, possibly according to its physical properties; if the material was fired, and the way it was done (BENGHEZAL, 1994A; NUNGÄSSER AND MAGGETTI, 1978; MARTINEAU AND PÉTREQUIN, 2000).
## 1.3 AIM OF THE STUDY

A major contribution of LEUZINGER's work (2000) was to precisely map the different houses of the village of Arbon Bleiche 3 and date their erection. A well described stratigraphy of the excavation permitted DE CAPITANI (2002) to correlate ceramics with stratigraphic beds and houses.

In Arbon Bleiche 3 as in other sites, archaeologists assume that certain kinds of forms or different thicknesses of the ceramics could reflect different provenances of the potteries.

De Capitani also provided typological grouping of ceramics, with possible relation to other countries. Summarising her results, Pfyn / Horgen pots and the special forms Pfyn were locally made in the village of Arbon Bleiche 3, whereas the special forms Bayern could be typologically related to the Bavarian area,

and the special forms Boleráz to the western Carpathian Basin. The undetermined special forms did not show any parallels with known forms and could not be attributed.

This study shall answer the following questions:

1. Which kind of clay was used to manufacture the archaeological material?

2. How were the ceramics tempered?

3. How were they shaped (coil-build technique or in a different way)?

4. How were they fired?

5. Was the clay used to build the walls of the houses (cob) also employed for ceramic production?

6. Is it possible to detect imported ceramics in Arbon Bleiche 3? Is there a possible connection between the ceramics from Arbon Bleiche 3 and those of the western Carpathian Basin?

7. Were the ceramics from Arbon Bleiche 3 produced in a domestic way (as defined by Pétrequin et al., 1994)?
2 - A NEOLITHIC VILLAGE IN SWITZERLAND:
DESCRIPTION AND HISTORY OF ARBON BLEICHE 3

**2.1 GENERALITIES ON THE NEOLITHIC PERIOD**

From the end of the Palaeolithic, a general and
rapid sea transgression, induced by the climate amel-
ioration and the glacial melting made sea water levels
rise. In the Neolithic, the sea levels were very similar
as those of today (MOHEN AND TABORIN, 1998). In
Europe, between 5500 BC and 2200 BC, hence during
the Neolithic period, the temperate oceanic climate is

very similar to the today situation. At the end of this
period, the climatic optimum induced an annual aver-
age temperatures of about 2°C higher than today.

The man was a hunter and a gatherer in the
Mesolithic, before becoming a producer in the
Neolithic, creating for the first time his own food by the
domestication of plants and animals. Domestication
means that man totally controls the biological cycle of
animals: the latter are protected, which involves a
forced development of the species and modifies the

<figure><img src="image_3.png" /><figcaption>Figure 2.1: Neolithic and ceramic diffusion paths in Western Europe. Contacts between the main paths are probable (D'ANNA ET AL., 2003).</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Figure 2.2:** Extension of the ceramic production as a function of time (LITZOW, 1984).</figcaption></figure>
natural evolution. Men adapted their environment by the clearing of trees and exploiting the forest to implant new cultures, pastures and villages. Agriculture and breeding were widely practiced and accompanied by sedentary life. However, the exploitation of arable ground, interrupted with fallow, can only be made for several years. New fields have to be then searched, which involves cyclical moving of villages or migrations. The transition to a production economy corresponds to big changes that are underlined by new techniques like stone polishing and ceramics modeling (PHILIBERT, 2000; GUILAINE, 2003). The proper characteristics of the Neolithic are the domestication of animals (except dog) and the production of ceramics.

Figure 2.1 shows the diffusion of these two cultural features from Near-East to Central Europe (D'ANNA ET AL., 2003). The new way of life diffused to the Mediterranean south-east, to the Balkans and the Danube Basin. From there, the progression separated into two directions: the Mediterranean current followed the Adriatic shores to Italy and southern France, whereas the continental current crossed the Danube plains to the Rhine and Elbe valleys to finally reach the Paris Basin. The propagation is presented as a progressive acculturation between neighbours by adopting better ways of living and knowledge. In the Danube valley and in southern Moravia, the Neolithic began around 4750 BC (Fig. 2.2). Five centuries later, a massive production of ceramics with linear or curved ornaments propagated to the Paris basin. Figure 2.3 shows this East to West movement. Note that the Danube River is a preferential path. The motives on the ceramics are relatively uniform from the Danube to the Paris region, which implies a rapid transmission of the know-how. The principal motives are undulated lines, lying S, horse-shoe or angular lines. Little motives are grouped points, lines, crosses, V- and U-forms. A few centuries later, a new Danube way of life conquered the whole Europe developing farming and big trapezoidal houses for several families (MOHEN AND TABORIN, 1998).

CAMPS (1990), PHILIBERT (2000) and GUILAINE (2003) propose that the ceramic process was invented at different places; imagining one single place in which the ceramic production was developed and this technique afterwards widely distributed is very improbable.

The period between the fifth and the third millenary before Christ is characterised by the growing importance of favouring a minority. Localities of more importance, defensive architecture and spectacular funeral monuments were signs of social distinction.

The extraction of blocks of stone for megaliths, the weight of which was up to 300 tons, their transport on several kilometres and their erection surely necessitated the presence of an authority to decide and coordinate labour. Some beautiful special tools, found in Neolithic tombs, are indicators for a hierarchical society (axes of alpine jadeite in Carnac, gold and metal treasuries in Varna, Black Sea; GUILAINE, 2003). This hierarchy gets along with the emergence of an economical system based on the development of handcraft, exchanges of prestige goods, and intensification of production abilities (PHILIBERT, 2000).

Silex extraction sites appeared in the early Neolithic as open mines or galleries, the main ones situated in Grand-Pressigny (Indre-et-Loire, France). Several hundreds of kilometres often separated these mines from the production area of the tools. Such an increase of distances and of travelling material that could exceed 800 km differentiates Neolithic from former periods.

During Neolithic specialised competences emerge: people that produce tools become specialised and depend on exchanges. Know-how is not any more bound to one individual in a group, but to one distinct group. A new techno-economical organisation emerges: one group furnishing tools depends on another furnishing food involving a new equilibrium due to exchanges and trade (PHILIBERT, 2000).

The Neolithic period in Switzerland is delimited between 5500 BC and 2200 BC (STÖCKLI ET AL., 1995). The second phase of the Neolithic (around 4600 BC to 3200 BC) is characterised by the expansion of the Neolithic economy, by the human impact on landscape and by the apparition of the first grouped vil-

<figure><img src="image_5.png" /><figcaption>Figure 2.3: Propagation to the Paris Basin of the linear ceramics (MOHEN AND TABORIN, 1998).</figcaption></figure>
lages, such as lacustrine sites. Important homogeneous cultural human groups formed, keeping preferential material and spiritual relations with their region of origin, and using more and more complex funeral rituels (VORUZ, 1991).

For various reasons – inhumations as funeral ritual, ornaments of the ceramics evolving from deep perforations to linear incisions, first copper metallurgy between 3600 and 3500 BC – it seems that the north-eastern part of Switzerland had preferential relations with southern Germany (Altheim culture), and kept a cultural heritage from their Danube ancestors (VORUZ, 1991).

<figure><img src="image_6.png" /><figcaption>**Figure 2.4:** Representative pottery forms from the Neolithic cultures of western Switzerland. Cortaillod culture: A: Jar with globular body, S-shaped profile, with knobs under the lip; B, C: Deep plates with perforated knobs placed side by side; D: Carenated bowl; E: Bowl with concave walls; Late Cortaillod culture: F, G: Jars with flat bottom; H: Deep plate; I: Deep S-shaped bowl; Port-Conty culture: J: Cooking pot with a rim and knobs at the shoulder; K: Cooking pot with flat bottom; Western Horgen culture: L, M: Conical to cylindrical jars with round or vertical lips reduced to a ridge; N: Jar with slight everted lips; O, P: Lips underlined by a ridge and sometimes knobs (drawings from STÖCKLI ET AL., 1995).</figcaption></figure>

## 2.2 THE NEOLITHIC CULTURES IN SWITZERLAND

The duration of the cultures proposed here are coming from VORUZ (1991); the descriptions of the ceramics and the pictures are taken from STÖCKLI ET AL. (1995).

### 2.2.1 Western Switzerland

In western Switzerland, the Cortaillod culture began in 4500 BC and ended in 3800 BC. In the early period, it produced black fine smoothed ceramics. 90% of the vessels are jars with a globular body and an S-shaped profile decorated with knobs under the lip (Fig. 2.4A), together with deep plates with perforated knobs placed side by side (Fig. 2.4: B, C). Bowls are seldom (Fig. 2.4: D, E).

<figure><img src="image_7.png" /><figcaption>**Figure 2.5:** Representative pottery forms from the Neolithic cultures of Central Switzerland. Cortaillod culture: A, B, C: Jars with flat bottom, S-shaped profile, A and C with knobs under the lip, B with perforated knobs on the body; D, E: Carenated bowls, D with perforations, E with perforated knobs on the carene; F: Plate with juxtaposed perforated knobs on the bottom; Late Cortaillod culture: G, H: Jars with flat bottom and S-shaped profile, G with knobs on the lip; I: Bowl with convex body, simple rim and flat bottom; J: Deep plate; Pfyn culture: K, L, M: Jars with S-shaped profile, flat bottom and elongated lower body, K and L are coated with barbotine, K with finger prints on the lip, M with knobs on the lip; N: carenaed bowl with flat bottom; O: Jug with handles (drawings from STÖCKLI ET AL., 1995).</figcaption></figure>
Between 3750 BC and 3500 BC, late Cortaillod developed and the ceramics had coarser walls with a simplified repertory. Almost 80% of the vessels are jars with a flat bottom (Fig. 2.4: F, G); deep plates represent less than 10% (Fig. 2.4H) and bowls are seldom (Fig. 2.4I). Perforated knobs become rare.

Between 3500 BC and 3200 BC, a cultural impoverishment in the ceramics happened during the Port-Conty Culture, which made the transition between Cortaillod and Horgen civilisations. The cooking pots have then usually flat bottoms, their walls are slightly widening out with a rim and knobs at the shoulder (Fig. 2.4: J, K).

Between 3200 BC and 2800 BC, during the Horgen culture, this impoverishment is clear: the walls are coarser, the jars conical to cylindrical and the lips reduced to a simple ridge. The knobs appear very seldom (Fig. 2.4: L-P).

### 2.2.2 Central and eastern Switzerland

The Cortaillod culture of central Switzerland began in 4250 BC and finished in 3500 BC. The

ceramics are typologically similar to those of the Cortaillod culture of Western Switzerland. Jars and cooking pots with flat bottom, together with deep plates with perforated knobs are predominant whereas bowls are seldom (Fig. 2.5: A-F).

Between 3900 BC and 3600 BC, the Cortaillod civilisation-neighboured the Pfyn Culture. The ceramics of Late Cortaillod are simplified, often with a flat bottom and rare knobs (Fig. 15: G-J). The vessels of the Pfyn culture are jars often covered with barbotine, with S-shaped profile, flat bottom, elongated lower body and rare knobs (Fig. 2.5: K-M), carenated bowls with flat bottom (Fig. 2.5N) and jug with handles (Fig. 2.5O). Thin walls, ornaments composed of finger impressions on or under the lip, simple decorations of lines, points and finger pinches are also characteristic, together with copper crucibles (BILLAMBOZ AND SCHLICHTHERLE, 1985).

In eastern Switzerland, the Pfyn culture began in 3950 BC and is characterised by vessels with a flat bottom, jars with S-shaped profile and elongated lower body, with rimmed lip and often coated with brushed barbotine (Fig. 2.6: A-D).

Between 3700 BC and 3500 BC, late Pfyn induced a higher percentage of cooking pots and a depreciation of the esthetical quality of the whole ceramic,

<figure><img src="image_8.png" /><figcaption>**Figure 2.6:** Representative pottery forms from the Neolithic cultures of Eastern Switzerland. Pfyn culture: A, B: Jars with S-shaped profile, flat bottom and elongated lower body, B with rimmed lip and coated with brushed barbotine; C: Carenated bowl with flat bottom; D: Jug with handle; Late Pfyn culture: E, F: Jars with S-shaped profile, flat bottom and elongated lower body, coated with barbotine and with knobs on the lip; G: Carenated bowl with flat bottom; H: Jug with handle (drawings from STÖCKLI ET AL., 1995).</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Figure 2.7:** Representative pottery forms from the Late Neolithic cultures of Eastern and Central Switzerland. Eastern Horgen culture: A, B, C: Cooking pots with sub-cylindrical profile; Late Horgen culture: D: Cooking pot with cylindrical profile; E, F, G: Cooking pots with cylindrical profile and sometimes perforations on the lip (drawings from STÖCKLI ET AL., 1995).</figcaption></figure>
which has then thicker walls (Fig. 2.6: E-H).

From 3250 BC to 2750 BC, the Horgen culture is to be found in central and eastern Switzerland with the emergence of cooking pots with a quite cylindrical profile, and with thick and rough walls (Fig. 2.7: A-C). In the late Horgen times, the repertory of the vessels is very simplified: the most frequent ceramics are coarse walled cylindrical jars with rare perforated lip (Fig. 2.7: D-G). Figured stamped or incised drawings are new. They are made of abstract sketches or characters, solar motives and even houses and landscape (HÖNEISEN, 1985).

Note that Arbon Bleiche 3 (3384-3370 BC) developed during the transitional period between Pfyn and Horgen cultures.

### 2.2.3 Life during the mid-Neolithic period

The mid-Neolithic period is defined in the literature between 4600 and 3200 BC (VORUZ, 1991). We will focus on this period, because it includes the den-drochronological data obtained in Arbon Bleiche 3 (3384-3370 BC). Many innovations modified the life conditions of the mid-Neolithic societies: first villages, first agricultural systems, inhumations with numerous ornaments, imports of metallic objects followed by first copper metallurgy, pirogues and fishing material, cooking pots, etc. This period is characterised in Switzerland by the beginning of the lacustrine com-

munities. Hunting concentrated on deer, whose horns were intensively exploited (DE CAPITANI ET AL., 2002). Culinary practices changed also, because the ceramic material permitted to cook. The modification of the ceramic material between Pfyn and Horgen cultures shows a restriction of the vessels repertory and a coarsening of the walls. These facts shall not be interpreted as a lowering of quality, but as a transfer; the idea of beauty is not any more to be found in ceramic, but in wood vessels, axes, knives, horn tools, etc. (VORUZ, 1991).

The concentration of typologically similar vessels in every domestic unit let BLEUER (1993), GERBER ET AL. (1994) and MARTINEAU AND PËTREQUIN (2000) think that every household made its own ceramic according to its needs. Ethnology associates the production of ceramics to women work, together with the cooking of goods.

During the winters of 1853-1854 and 1890-1891, the water level of the lakes lowered and wooden piles were observed in several Swiss and French lakes (Fig. 2.8, SCHIFFERDECKER, 1985). Ethnological comparisons led to the hypothesis of a wooden platform on which houses were erected, the platform being connected to the land with a foot-bridge (Fig. 2.9, KAESER, 2004). The well-preserved material excavated in the Neolithic sites permits to reconstruct the house structures and to draw their evolution. Recent excavations showed several variations in their construction: in Yverdon (VD), the houses were built on piles in the border of the lake; in Chalain (F) and Tayngen-Weier (SH), they were built on wooden floors, whereas they were laid directly on the ground in Portalban (FR), Egolzwil (LU) and Charavines (F). In all these cases, the villages were erected on the lake shore (Fig. 2.10) and not in shallow water. The proximity of the Alps induced, with the melting of snow in spring, a seasonal variation in the water of the lakes. Hence, some villages may have been erected on areas inundated during a part of the year (CORBOUD, 2001).

The abandon of villages were frequently provoked by a rise of the water level and the inundation of the houses. Moreover, the archaeological objects are often covered with sterile lacustrine sediments that deposed in high water and that protect the remains (CORBOUD, 2001).

The place of burial corresponding to a Neolithic village is only rarely evidenced. In the case of the lacustrine villages of Switzerland, the graves are frequently unknown (HÖNEISEN, 1985).

<figure><img src="image_10.png" /><figcaption>**Figure 2.8:** During several winters of the 19th century, the water level of the lakes lowered and wooden piles were observed in several lakes, here in Cortaillod (LOUBOUTIN, 1998).</figcaption></figure>
## 2.3 PRESENTATION OF ARBON BLEICHE 3

### 2.3.1 Geography

Arbon is today a little city in the north-east of Switzerland, on the southern shore of Lake Constance (Fig. 2.11). The southern fields of the city, where the excavations took place, are named Bleiche (Fig. 2.11). The land, very flat, lies about 400 meters over sea level. Small straight streams cross the land to the lake. The excavation lies at 670 m from the actual shore.

The first location of a lacustrine village on the Bleiche was discovered in 1885 when a draining network was excavated. Other villages neighbouring the first one were put into light in 1944. Since then archaeological excavations were done in three large areas of the Bleiche. The third one, named Arbon Bleiche 3

will be discussed in this work. All these areas are distributed on an east-west line in a 500 m perimeter. They were undoubtedly situated on the very shore of the lake in the Neolithic, as often described in other places in Switzerland.

The sedimentary beds containing the archaeological material are situated between 393.90 meters over sea and 397.00 meters over sea (mos). The higher, northern part of the Neolithic village culminates at 396.20 mos and the area extends in gentle slope to the south to 394.00 mos. The 400 m curve, which can be observed on figure 2.11, can be regarded as the maximum water level in the Neolithic period.

About three kilometres south and west from the excavation, small hills rise to 650 m.

<figure><img src="image_11.png" /><figcaption>**Figure 2.9:** Lacustrine villages constructed on a wooden platform connected to the land with a foot-bridge (left: painting of BACHELIN, 1867, Swiss National Museum, Zürich; right, drawing of TROYON, 1857, in KAESER, 2004).</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Figure 2.10:** Neolithic villages erected on the lake shore (left, picture of GUBLER, 1996, Swiss National Museum, Zürich; right: model of Egolzwil 5 LU, from HÖNEISEN, 1985).</figcaption></figure>
### 2.3.2 Geology

The hills are composed of Tertiary sediments, the Molasse, the beds of which appear when the Quaternary cover (Würm moraines from the Rhine glacier) is eroded by streams, rivers and in artificial excavations (Fig. 2.11).

Three main geological deposits have to be described to understand the environment in which the Neolithic village stood. First, the eldest beds are Tertiary sediments (Molasse), which dominantly consists of carbonate-rich deposits (yellow on Fig. 2.11); second, the

Quaternary Rhine Glacier Moraine, deposited during the Riss (blue on Fig. 2.11) or during the Würm (greenish on Fig. 2.11), that is either carbonate- or silicate-rich; and third, the late Quaternary lacustrine sediments, which are the foundation of the Neolithic village and its subsequent covering strata (white on Fig. 2.11).

The Molasse present as basement in the region of Arbon is the Upper Freshwater Molasse formed during the Middle Miocene, between ten and fifteen million years. It is composed of various sedimentary beds of silts, marls and shales, often yellow to beige. These

<figure><img src="image_13.png" /></figure>

**Figure 2.11:** Geological map of the surroundings of Arbon with the emplacement of the excavations of Arbon Bleiche 3. The red line in the centre of the picture is the 400 m curve, which represents the maximum water level in the Neolithic. JB300-JB310 are the finding places of the local clays. The black circle is the perimeter of 2.5 km around the archaeological site in which the clays were searched (Map from the geological atlas of Switzerland, sheet 45, 1:25.000, 1075 Rorschach, Schweizerische geologischen Kommission, Bern, 1964)
beds are the result of the erosion of the Alps Mountains and were deposited in an ancient lake.

During Quaternary (before 1.5 million years), at least four phases of glaciations modified the Swiss landscape. Riss and Würm were the two most important (respectively from 300'000 to 120'000 and from 80'000 to 12'000 years before present). In these times, the Rhine glacier was covering North-East Switzerland to the Lake Constance (HANTKE, 1993). When it retired, important sedimentary deposits, the moraines, were deposited in the surroundings of this lake, often in little lakes formed in front of the dropping glacier (fluvio-glacial or fluvio-lacustrine deposits). These deposits are still present on the shores of Lake Constance; they are composed of non-compacted sediments of any size: the huge blocks are named erratic blocks; middle-sized deposits contain pebbles with sand and clay, whereas the fine-sized are shales often mixed with sand particles. The erratic blocks as well as the pebbles consist of a great variety of lithologies, including granites, gabbros, rhyolites, cherts, etc. They were all transported from the Rhine catchments in the Eastern Swiss Alps (WEGELIN, 1936).

During late Quaternary (postglacial ages: < 10'000 years), the erosion of the Alps continued and new beds deposited in the Swiss lakes. Those of Lake Constance were fine (often clays) because the source of the Rhine River was far. These beds were observed in the basement of the excavations. They are silts and fine sands, quite similar to lacustrine chalk (calcareous lake deposits). They can be differentiated from this latter by their lower content of carbonates (less than 56%) and too abundant fragments of algae and molluscs shells (Characea, Fig. 2.12: A, B, C; Ostracods, Fig. 2.12: D, E, F) (HOCHULI, 1994).

<figure><img src="image_14.png" /><figcaption>**Figure 2.12:** A: Algae Chara vulgaris; B: seeds of charophytes that are found in thin sections (C). D: living ostracoda, an: antennae, e: eye; E: both separated valve of an ornated ostracoda (Devonian), F: and of a smoothed one (Jurassic) (FOUCAULT AND RAOULT, 1992)</figcaption></figure>

### 2.3.3 Dendrochronology

The chronological frame is well established with the help of dendrochronological dating (LEUZINGER, 2000). The first house was built in 3384 BC. During the following years, 26 new houses were erected forming rows separated by narrow lanes (Fig. 2.13). Around 3370 BC a fire destroyed the village. Since then the village was abandoned. The settlement was occupied for a very short period: only 15 years.

As said before, in eastern Switzerland, the Pfyn culture is dated between 3950 and 3500 BC, followed by the Horgen culture (3250-2750 BC) (VORUZ, 1991; STÖCKLI ET AL., 1995). The village of Arbon-Bleiche 3 was therefore occupied during the poorly known transitional period between Pfyn and Horgen cultures. Several characteristics of the material are of Pfyn tradition, but others are already bound to the coming Horgen culture. This cultural change is not abrupt, but is a continuous development from Pfyn to Horgen forms (DE CAPITANI, 2002).

<figure><img src="image_15.png" /><figcaption>**Figure 2.13:** Schematic map of the excavations 1983 and 1993-1995 of Arbon-Bleiche 3 with the location of the different houses, their dating by dendrochronology, and the trace of square meters (modified from DE CAPITANI, 2002).</figcaption></figure>
# 3 - THE NEOLITHIC CERAMICS IN ARCHAOMETRY: STATE OF THE ART AND DEFINITIONS

## 3.1 INTRODUCTION

As described in MAGGETTI (2001, 924), “the lifespan of a piece of pottery can be divided into five steps: (1) extraction of the clay from the pit; (2) manufacture of the object (processing of the clay, firing); (3) use, with subsequent breakdown; (4) burial; (5) excavation, cleaning, treatment and analysis”. Hence, the chemical analysis of a sherd will reflect “the composition of the original clay, its processing (the extraction of coarse, a-plastic particles or the addition of temper fragments can change the chemistry), the use of the object (e.g. the chemical composition of a cooking pot can be affected by reaction processes between the pot itself and the food), the burial stage (infiltration of foreign matter into the ceramic body or extraction of sherd matter caused by solvents from invading solutions) and the post-excavation treatment (e.g. cleaning with acids can lead to dissolution of carbonates)”. These different transformations of the clay will be discussed here.

## 3.2 COMPOSITION OF THE CLAY

### 3.2.1 Clay

According to CORRENS (1968), quoted in Heimann and FRANKLIN (1980, 24), “the mechanical mixture [called clay] consists of four main components: (1) The fine-grained weathering relics: quartz, feldspar, micas; (2) Neo-formations i.e. the clay minerals, as such, that are formed during weathering: kaolinites, halloysites, montmorillonites and illites; (3) Remainders of organisms: calcium carbonate (shells), silica (chert), carbon; (4) Neo-formations that occur after deposition: pyrite, dolomite, glauconite”.

The first group of components is often defined as natural inclusions or non-plastic elements, whose sizes are often less than 20 µm in diameter (NUNGÄSSER AND MAGGETTI, 1978). The second one (the argillaceous minerals) is made of weathering residues such as: feldspars partially leached in a humid climate transform to smectites, keeping their Mg2+ and Fe2+ ions; when totally leached, they turn to kaolinites. Micas, partially leached, form illites, main components of most Swiss clays. Clay minerals have grain sizes smaller than 2 µm in diameter and therefore are too fine-grained to be studied by the methods of optical mineralogy. They require to be studied by X-ray analysis because X-rays have much shorter wavelengths than visible light.

Often the first thing a potter does is to prepare the clay that will be fired to make a ceramic: it is rare to find a local clay in which the clay minerals and the non-plastic elements are mixed in a right proportion. The clays, very frequent in nature, have a very variable composition, which is linked to the kind of impurities present with or inside the argillaceous minerals. Quartz is always present in clays (clays containing much quartz are called shales), often with carbonates (the carbonate-rich clays are described as marls); other detrital minerals are also to be found in a natural clay (epidotes, zircons etc.). The prehistoric potter probably used preferentially naturally heterogeneous clays containing much silicatic natural inclusions. He also surely mixed clays of different origins (DE CAPITANI, oral communication).

Choosing good clay can reduce the risk of spalling. For example, clay containing montmorillonite has “extreme plasticity and high shrink / swell ratio that are difficult to overcome by the mechanical expedient of adding temper. Even a small amount of montmorillonite will significantly alter the workability of a clay body” (GRIM 1968 in STIMMELL ET AL., 1982, 220).
### 3.2.2 Temper

The temper is all the non-plastic materials that the potter voluntary adds to the clay when it is too fat and too plastic. The higher the proportion of fine-grained particles, the longer the drying time, the shrinkage and the deformations. During drying and firing, the water is expelled and can cause profound shrinkage and frequent spalling of the ceramic object. Adding temper reduces this inconvenient. Moreover, potters used the adding of temper to increase the workability of clays, so that they could be easily formed into vessels. The voluntary introduction of temper has been present since early Neolithic. The most common temper is of mineral origin, and mostly local: crushed crystalline rocks, calcite or alluvial sands. The temper crushed from previously heated pebble stones of, for instance, granite and serpentinite is described as splintered and sharp-edged fragments by MAGGETTI (1994). Crushed calcite is easily recognisable in thin sections, because it disintegrates into cleavage rhombohedra. Limestones and calcite turn to lime in a firing process at 750°C, which inconveniently often implies the breaking of the ceramics. Grog, small fragments of fired broken ceramics, is also frequently used to temper vessels. Other materials of biological origin were also used as temper, such as shells, straw and other vegetable elements or fragments of bone (CAMPS, 1990; HARDMEYER ET AL., 1995).

Increasing the proportion of temper or using shell temper instead of rock pieces can also reduce the risk of spalling: "Shell temper is more effective than either limestone, quartz or grog temper in minimising the crack propagation and, thus, in reducing the risk of ultimate failure due to the stresses resulting from a rapid change in temperature" (TITE AND KILIKOGLOU, 2002, 2).

The addition of organic material, such as chopped

straw, produces an artificial porosity when fired and increased the sherd's resistance to changes in temperature (MAGGETTI 1994, 29).

LIVINGSTONE SMITH (2000, 24) studied the way the clay was processed in northern Cameroon: "treating the raw clays consists of "tempering" and kneading them. The materials selected for temper are (1) a dried and ground raw material (the temper is the same as the raw clay), (2) another clay, (3) sand, (4) crushed rock, (5) grog, (6) ashes and/or (7) dung. Most of these materials, available everywhere in the area, may be used alone or combined. When asked about the reasons for altering the clay in these ways, potters invariably answer that they are a necessity. Non-tempered clay would not stand drying or firing. Pressed further, they often admit that, in fact, tempering is primarily the best way to adjust the plasticity of soaked clay. The material chosen for tempering depends on how one was taught. As put by an old potter, "using one technique or the other is essentially a question of habit". While it appears that potters do modify the compositional and textural characteristics of the raw material, it is clear that these modifications and the tempers selected for this purpose are the result of choices made by the artisans between equally viable options" (LIVINGSTONE SMITH 2000, 31).

### 3.2.3 Discussion

The important separation between clay and natural inclusions on the one hand and tempers in the other hand will permit to deduce the manufacturing of the ancient potters. The petrographical study permits to distinguish between these components and will permit to split diverse tempers (rocks vs. grog vs. organic material, for example).

<figure><img src="image_16.png" /><figcaption>**Figure 3.1:** A, B: kneading with the hands (SANDERS, 1976) and C: with the feet (RADA, 1991).</figcaption></figure>
## 3.3 PROCESSING THE CLAY

### 3.3.1 Forming techniques

Once the clay and temper were prepared, mixed with water and kneaded with the hands or the feet (Fig. 3.1) to obtain a well homogenised paste, several forming techniques can be used to manufacture a ceramic. These techniques are presented in HUYSECOM (1992), GOSSELAIN (1999, 2001) and VELDE AND DRUC (1999) for example, and the main ones are described here.

Casting (Fig. 3.2A) is a technique in which the clay is pounded into a mould. In the coiling technique (Fig.

3.2: B, C; Fig. 3.3) a lump of paste is rolled between the hands or on a flat surface to make a long rope. Then, these coils are placed one on top of the other, in rows, to build the walls of the pottery. Coil thickness and length vary as a function of the size of the pot, the wall thickness, the ability of the potter, etc. The coils can be long and assembled following a spiral (Fig. 3.2B; Fig. 3.3) or as short as the diameter of the pottery and superimposed in circles (Fig. 3.2C). The coils are sealed together with water and hand pressure and the walls thinned by vertical movements of fingers. Pots break preferentially along these junction lines, which stay fragile. A very big ring can also be simply drawn (Fig. 3.2D). The moulding technique is shown

<figure><img src="image_17.png" /><figcaption>**Figure 3.2:** Different forming techniques: A: casting, B, C: coiling; the coils can be long and assembled following a spiral (B) or as short as the diameter of the pottery and superimposed in circles (C). D: drawing of a ring, E: moulding, F: drawing (GOSSELAIN, 1999).</figcaption></figure>
on figure 3.2E; the clay lump is applied over a mould and pressed down with the hands and eventually hammered. With the drawing technique (Fig. 3.2F), the ceramic is formed by drawing up a clay lump after opening it with the fingers or the fist. In the flat plate technique, also called slab building technique, clay slabs are flattened to a desired size, usually rectangular, then wetted and joined. Finally, the wheel-thrown technique, known as "tournette" (manually or with the feet rotated, without continuing rotation) is often described as a large piece of broken pottery set over a wooden support. The lump of clay is set over the rotating wheel and modelled (Fig. 3.4).

The most common forming techniques to finish the building process are the beating and the paddle-and-anvil techniques. In the first case, the paddle (often a

wooden flat piece) is beaten on the external surface of the piece, the hand of the potter inside the ceramic to retain the beating. Second, the paddle beats the external surface as the anvil (a round rock, a clay tool or a wooden "mushroom", Fig. 3.5) is used to counteract the paddle. These latter are used as secondary techniques to strengthen the walls and lift them up.

When observing an ancient ceramic, fractures between sherds are frequently visible. Horizontal fractures sometimes underline coils, but in the case of a good beating, these separations can disappear. Multi-directional fractures between sherds often do not permit to favour a forming technique more than another.

<figure><img src="image_18.png" /><figcaption>**Figure 3.3:** Coiling technique: the long coils are placed one on top of the other and assembled following a spiral to build the walls of the pottery. Then, they are sealed together with water and hand pressure and the walls thinned by vertical movements of fingers (SANDERS, 1976).</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>**Figure 3.4:** A: Wooden statue of a Egyptian potter with a hand turntable; B: pottery hand turning in Morocco (picture A. DESBAT, D'ANNA ET AL., 2003)</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>**Figure 3.5:** The paddle-and-anvil technique: the paddle beats the external surface as the anvil (a wooden "mushroom" in this case) is used to counteract the paddle (HUYSECOM, 1992).</figcaption></figure>
### 3.3.2 Surface treatment

Frequent post-firing treatments are organic coatings, smoking or soaking deposited on the vessel just after the firing. The more frequent is putting the red-hot ceramics into grass or leaves until they become black. For GOSSELAIN AND LIVINGSTONE SMITH (1995) they constitute one of the most unrecognized stages of the manufacturing process. In Cameroon, for example, "an organic mixture prepared by boiling, soaking or infusing parts of at least 26 plants or trees is either sprinkled on the pots when they come red-hot from the fire or rubbed on after cooling". Coating practices allow an increase of thermal effectiveness by waterproofing the vessels.

## 3.4 FIRING

### 3.4.1 Firing techniques

Archaeologists and ethnologists have proposed two major techniques of firing used during Neolithic times. First, open or bonfire firing (Fig. 3.6A); second, pit firing (Fig. 3.6B).

In a bonfire firing, the ceramics are piled on the ground and covered with fuel like wood, dung or grass. The fuel burns rapidly (about half an hour), but still gives high temperatures (up to 940°C, VELDE AND DRUC, 1999). Often, the firing temperatures vary from around 300°C and 900°C (Fig. 3.7; GOSSELAIN, 1992). This structure of fire does not permit a plateau of high temperature, and irregularities in the firing process, such as high temperatures reached in a very short time are frequent. Due to their proximity to the fuel, some parts of pots can be over-fired whereas others are under-fired. The firing temperatures obtained with this technique produce combustion smokes made of water vapour, acids of firing woods

<figure><img src="image_21.png" /><figcaption>**Figure 3.6:** Sketches of bonfire (A) and pit firing (B): in A the ceramics are heaped up on the ground, whereas in B they are mostly placed in a hole in the ground (VELDE AND DRUC, 1999).</figcaption></figure>

and firing wood tars. These smokes can penetrate some millimetres of the surfaces of the ceramics and induce their black coloration. The ceramics also often contain organic matter (straw, grass, hair, etc.) in the matrix and/or as temper that induce the same phenomena. Around 750°C (as a function of the firing time and of the oxygen fugacity), in an oxidising firing, the carbonates turn into lime, the tars are oxidised, and the sherds turn red.

The pitfiring differs from the bonfire by a shallow hole in the ground. The ceramics are piled in the hole and covered with fuel. The ground maintains the heat around the ceramics during a longer time and permits a more constant firing. Even if the temperature rises as rapidly as in a bonfire, the primary inflammation is less violent; the temperature rises more regularly and is maintained during a longer time, as is the cooling time. The air entering the fire at the end of the process permits the combustion of the tars, which will give

<figure><img src="image_22.png" /><figcaption>**Figure 3.7:** Temperature ranges for the five kinds of firing described in GOSSELAIN (1992): A: Open firing, B: open firing with sherds covering the pots, C: pit firing, D: pit firing with sherds covering the pots, E: updraft kiln firing. The shaded area comprises more than two thirds of the ethno-thermometric data, and is in every case situated between 600 and 900°C (from GOSSELAIN, 1992).</figcaption></figure>
ceramics grey to red coloration and a black core in the sections. Pit firing in regard to bonfire induce many technical improvements (ARNAL AND ANDRIEUX, 1991; GOSSELAIN, 1992, 1995; LICKA, 1991).

GOSSELAIN (1992, 244, 246) discuss five different types of firing structures (Fig. 3.7): open firing, open firing with sherds covering the pots, pit firing, pit firing with sherds covering the pots and updraft kiln firing. If a firing temperature is proposed for a group of ceramics and if this temperature is between 600°C and 900°C (dashed area on Fig. 3.7), the firing structure used cannot be deduced. Only in some rare cases, i.e. when the firing is less than 450°C or more than 950°C, the structure can be determined, respectively open and kiln firings.

Fuels used do not seem to influence the temperature. Considering the data on the time needed to reach maximum temperature, it is clear that the heating rate is the most specific parameter for each firing technique. “On average, 22 min are needed to reach the maximum temperature in open firing, 60 min when a layer of sherds separates the vessels from the fuel, 41 min for pit firing, 114 min for pit firing with sherds and 259 min (4-5 h) for updraft kiln firing”.

LIVINGSTONE SMITH (2001) made a study on the different methods used to fire ceramics. He studied 80 firing procedures recorded around the world. He wrote that a thermal profile shall be defined in terms of maximum temperature, heating rate (the average temperature increase per minute until maximum temperature

is reached) and soaking time (the number of minutes the vessels remain above a certain temperature threshold, above 700°C in this paper). The technological study is made on four different parameters: the structure of the firing, the fuel used, the schedule based on the way the firing process finishes and the scale based on the number of vessels fired at the same time.

The firing structures studied are: bonfires, bonfires with light insulation, bonfires with heavy insulation (complete sherd covering), depressions, depressions with heavy insulation, pits, pits with heavy insulation, simple kilns (updraught kilns without firebox) and kilns (updraught kilns with firebox). The fuels are sorted into three categories: light fuel (dominant material is grass, straw, millets husks or stems, palm fronds etc.), heavy fuel (dominant material is wood or bark) and dung as dominant material. Two types of schedules are taken into account: interrupted processes (the vessels are drawn out of the fire while red hot) and slow cooling processes (the vessels are left to cool down in the structure). The scale ranges from one to over 600 pots fired at the same time, while the dimension of the structure varies from 0.5 to 7.5 m in diameter. It was divided into small scale firing (< 5 vessels), medium (6 – 60 vessels) and large scale firings (> 60 vessels).

This study leads to the following conclusions: different firing procedures may induce similar thermal profiles, as discussed in GOSSELAIN (1992). The simplistic opposition between the thermal characteristics of “open” and “kiln” firing does not take into account much technical and cultural information. The duration of both types of procedures is extremely variable. The upper range of maximum temperature is higher for kilns than for open firings. The heating rate of open firing ranges from a few degrees per minutes to over 120°C/min, while heating rates for kiln firings are below 20°C/min. However, kiln firings are not the only one to allow for very low heating rates, the lower range of heating rates for open firings being inferior to

<figure><img src="image_23.png" /><figcaption>**Figure 3.8:** Division of the section of a sherd into five distinct parts (modified from MARTINEAU AND PÉTREQUIN, 2000)</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>**Figure 3.9:** Schematic cross-section of a ceramic showing the un-oxidation of the inside due to its mouth down position on the ground (modified from VELDE AND DRUC, 1999).</figcaption></figure>
that of kiln firings. The soaking time above 700°C is about 20 minutes for both categories, the upper range of open firings being around 2 h, against 1 h for kilns, while both categories may also produce no soaking time above 700°C. Hence, be it from the point of view of “open” and “kiln” firings, or from the point of view of the various structures, fuels, schedules and scales, none of the technical categories induce specific thermal characteristics. In other words, it is impossible to relate a particular set of thermal characteristics (duration, maximum temperature, heating rate and soaking time) to a specific firing procedure, because very different characteristics may be achieved within the same structure and similar fuel.

Even if often not described and taken into account, the type of fuel “is an extremely important variable in the thermal cycle, due to its effect on the parameters of time (rapidity of lighting, duration) and temperature (effectiveness and economy), and on the nature of the solid volatile residue (coals and smoke)” (FABBRI ET AL., 2002, 192).

Whatever the firing technique used, a gentle firing reduces the risk of spalling: “The primary driving force for thermal shock is the stresses associated with the differential expansion or contraction of the inner and outer surfaces of a pottery vessel that are caused by a rapid change in temperature at one surface and the resulting temperature gradients through the vessel wall” (TITE AND KILIKOGLOU, 2002, 1).

### 3.4.2 Firing Atmosphere

In 2000, Martineau and Pétrequin conducted experimental firing of reproductions of Neolithic ceramics from Chalain (France). They observed that bonfire and pit firing techniques necessitate the description of five parts in the section of a sherd to understand the firing process: the section divides into the core, two margins and two surfaces (Fig. 3.8).

When ceramics are fired in a bonfire, during the rising of temperature, the fuel uses all the available oxygen. This induces always a reducing atmosphere for the ceramics. After reaching the maximal temperature, when the wood is consumed, the oxygen of the air begins to be in contact with the ceramics and the atmosphere turns to oxidising. In this situation, the ceramics are orange, sometimes with a grey core. Black marks stay on the external surfaces where the air is not in contact. If a very fine fuel is

used so that the oxygen cannot penetrate inside the firing after combustion, the atmosphere stay reducing and carbon completely blackens the ceramics. Another way to obtain a reducing cooling consists of interrupting the firing, taking away the incandescent ceramics and putting them into organic matter (i.e. grass, leaves) until they become black.

VELDE AND DRUC (1999) show that putting the ceramics mouth down onto the ground, the inside remains un-oxidised during firing because air cannot reach the inside (Fig. 3.9).

MARTINEAU AND PÉTREQUIN (2000) defined five firing phases in a bonfire firing:

- Phase I: Between 20°C and 400°C, the ceramic does not change its colour, remaining the same as the paste.

- Phase II: during the second part of the rise of temperature, the whole section of the piece becomes black.

- Phase III: on the peak of temperature, the section becomes clearer from the outer margin to the core.

- Phase IV: when the temperature decreases, two different possibilities were observed:

- Phase IVa: after its action on the outer margin (Phase III), the oxygen, which circulates less easily inside the ceramics than outside, makes the inner margin clearer before the core. If the duration of the cooling is long enough, the latter becomes also clear.

- Phase IVb: when the ceramics are close forms or if they are piled, the internal oxidation is more difficult, and the core becomes clear before the inner margin.

- Phase V: with the end of the decrease of temperature, the whole sherd becomes clear.

The black ceramics result from a confined atmosphere during the whole firing or only during the cooling. No sherds with inner oxidised margin and outer black margin were observed in the material of Chalain.

### 3.4.3 Experimental firing of clays

Several authors frequently made experimental firings on clays, in order to detect mineralogical changes as a function of temperature, time and fugacity of oxygen. The clays are normally fired in an electric oven in oxidising atmosphere, between 500°C and 1000 to 1200°C. In the laboratory of Fribourg, the temperatures are held constant for one hour at peak temperature to let the new minerals crystallise. The mineralogy of the fired clays are determined by X-ray diffraction. That way, the mineralogical changes of
one clay during a firing process are precisely described. Hence, most temperature estimations of ancient ceramics are indirect, as explained by TITE (1995). He quoted NORTON AND HODGDON (1931), who proved that “to a first approximation, increasing the time at maximum temperature by a factor of five is more or less equivalent to increasing the maximum temperature by approximately 30°C. Therefore, instead of trying to determine the actual maximum temperature reached during a firing, it is more appropriate to define an equivalent firing temperature which is the temperature maintained for one hour which would produce the observed mineralogy or microstructure”. The firing temperatures resulting from these experiments are only rough approximations of the firing temperatures attained in the Neolithic, because the firing conditions used by prehistoric potters were obviously different (rise of temperature not constant, temperature varying in the firing area, fugacity of oxygen, etc.).

### 3.4.4 Generalities on colour changes in the ceramic during open firings

For ANDRIEUX (1991), the best way to understand the coloration of the ceramics is by analysing the chemistry of the wood firing. The combustion of the wood into gaseous phases, varying with the rise of temperature, generates different firing atmospheres impregnating the ceramics in contact: until 750°C, the water vapour is the impregnation vector for the tars and soot, generating the black coloration of ceramics. Over 750°C, these tars and soot decompose, and the carbons (C, CO, CO₂), the oxygens (O, O²⁻) and the hydrogens (H⁺) are liberated from the tars. Only at about 900°C ceramics tend to get oxidised (reddish, orange or white colours) or reduced (grey colour, not black). Traces of the previous stages in the firing process remain visible in a thin section of the sherd, often appearing with a black core, even in this range of temperature.

The red colour of the sherd fired in an oxidising atmosphere is given by hematite (Fe₂O₃), which contains iron in its oxidised form (Fe³⁺). Apart of carbon, the grey to black colouration can be given by magnetite (Fe₃O₄) or hercynite that contains iron in its reduced form Fe²⁺; it can also be bound to the presence of manganese oxides, such as Mn-spinels (MnFe₂O₄), bixbyite (Mn₂O₃) and hausmannite (Mn₃O₄). These latter appear around 1000°C as a function of the percentage of Mn₂O₃ present in the clay: if Mn₂O₃ is between 20-40 wt.%, spinel and hematite form; if it is around 65 wt.%, bixbyite crystallises and if it is between 75-85 wt.%,

hausmannite is present (MAGGETTI, 1974; MAGGETTI AND GALETTI, 1986; LETSCH AND NOLL, 1983).

According to MAGGETTI (1979) and to HEIMANN AND FRANKLIN (1980), the change of the firing colour from red to brown at temperatures above 1100°C is strongly related to the presence of fayalite (Fe₂SiO₄). The brown colour is a mixture between the red of the hematite and the green of the fayalite.

WOLF (1999, 57) explained the colouration of fired clays as follows: “The progressive change from orange (500°C-900°C) to red (900°C-1100°C) then to brown-red (>1100°C) can be related to grain coarsening of hematite with increasing temperature (PETERS, 1969) and to small amounts of spinel which forms at high temperature”.

SIGG (1991) explained the difference of red and yellow colouration of the sherd: in CaO-rich clays, “if the ratio Al₂O₃ / Fe₂O₃ is more than 3 and less than 5, the fired sherd turn from red to pink. If it becomes higher than 5, the pink colour turns to yellow. If the ratio Fe₂O₃ / CaO is less than 0.5, the pink colouration turns also to yellow. Generally, the products stay yellow if CaO / Al₂O₃ is higher than 1, even if iron oxides increase”. A red burning clay can change its colour to yellow if CaCO₃ is added to the raw material.

### 3.4.5 Mineralogical transformations during experimental firings

#### 3.4.5.1 Introduction

As a summary, HERZ AND GARRISON (1998, 257) explained that during firing “the principal changes that take place are by (1) oxidation or reduction; (2) loss of volatiles and dehydration, principally loss of hydroxyl ions (OH) from the clay structure; and (3) formation of higher-temperature phases and finally, at very high temperatures of firing, (4) vitrification” (formation of a liquid). The presence of melt in the samples is evidenced by a rise of the background noise in the XRD pattern at T > 900°C in the CaO-poor samples and at T > 800°C in the CaO-rich samples due to the presence of an amorphous phase.

The crystalline and amorphous phases present in a sherd are of three types: (1) primary minerals (relic minerals inherited from the initial clay: i.e. quartz, clay minerals, calcite); (2) firing minerals (formed during firing: i.e. gehlenite, diopside, mullite) and (3) secondary minerals (formed after firing: i.e. portlandite, cal-
cite, gypsum) (MAGGETTI, 1982, 123; 1986, 94)

The mineralogy and chemistry of the clay imply the formation of new minerals during firing process: TITE ET AL. (1982, 63), summarising several authors, such as MAGGETTI (1979), explained that in CaO-rich clays (> 5% CaO), fired sherds are characterised “by the presence of a high concentration of calcium (and/or magnesium) silicates (anorthite, wollastonite, diopside, gehlenite). These silicates had been formed through the reaction between the calcium (and/or magnesium) oxide and the dehydroxylised clay minerals”. In contrast, in CaO-poor clays (< 5% CaO) “the formation of high-temperature crystalline phases was very much less pronounced. Only weak lines associated with spinel and mullite were detected”. Nöller and KNOLL (1988) fired a montmorillonitic and illitic clay mixed with varying quantities of CaCO₃. “The more Ca that is added the greater the extent of and the faster the formation of silicates. The Ca-rich material even shows a decrease in the amount of relatively stable quartz with the formation of extensive amounts of the calcium silicates gehlenite and wollastonite”.

For oxidising atmosphere of firing, the work of the following authors was taken into account: BÉARAT (1992); BÉARAT AND BAUER (1994); BENGHEZAL (1990, 1994a, 1999); COURTOIS (1973); CULTRONE ET AL. (2001); ECHALLIER AND MÉRY (1992); GRIM (1968); HEIMANN (1989); HEIMANN AND FRANKLIN (1980); HEIMANN AND MAGGETTI (1981); HERTLI ET AL. (1999); HERZ AND GARRISON (1998); JORNET (1980, 1982); JORNET AND MAGGETTI (1983); JORNET ET AL. (1985); KILKA (1987); KÜPFER AND MAGGETTI (1978); LETSCH AND NOLL (1983); MAGGETTI (1974, 1979, 1981, 1982, 1986, 1993, 1995B); MAGGETTI AND HEIMANN (1979); MAGGETTI ET AL. (1984); MAGGETTI ET AL. (1988); MICHEL (1985); MURAD AND WAGNER (1989); NÖLLER (1983); PETERS AND IBERG (1978); PETERS AND JENNI (1973); PICOUET (1997); STIMMELL ET AL. (1982); TITE (1995) and TITE ET AL. (1982).

For reducing atmosphere of firing, the literature is less abundant and the works used are the following: HEIMANN ET AL. (1980); HERZ AND GARRISON (1998); LETSCH AND NOLL (1983); MAGGETTI (1993); MANIATIS ET AL. (1983) and MURAD AND WAGNER (1989).

### 3.4.5.2 Problem of pressure and of thermodynamically incompatible minerals

As exposed in MAGGETTI (2001, 924), “in contrast to natural rock-forming processes, pressure is insig-

nificant in the genesis of [ceramics], because the kiln can be considered as a technical system. In such open systems, neither pore solutions, present before firing, nor gaseous reaction products, which may have been produced during the high temperature process, have an influence on the transformation, because they can leave the system at any time.” Hence, the new mineralogical associations produced during firing are high temperature minerals, but no high pressure minerals are observed.

MAGGETTI (1986) and HEIMANN (1989) explained the presence of thermodynamically non-compatible minerals side by side in ceramics. For MAGGETTI (1986), only small regions confined to the reactive interfaces between mineral grains are in equilibrium. HEIMANN (1989, 132) added that “the inherent inhomogeneity of the clay, together with low temperatures and short firing times, generate a thermodynamic non-equilibrium with respect to the global system.”

### 3.4.5.3 Lime popping

When fired over 600°C (oxidising atmosphere) or over 750°C-900°C (reducing atmosphere), calcite (CaCO₃) decomposes to lime (CaO) with production of CO₂. When exposed to the air, the lime reacts with moisture to form portlandite (Ca(OH)₂). Since the latter crystals have a larger volume than the original calcite crystals, this expansion forms cracks that can destroy the vessel (MAGGETTI ET AL., 1984; TITE AND KILIKOGLOU, 2002).

Methods to avoid this lime popping are well known by potters firing CaO-rich clays and listed in TITE AND KILIKOGLOU, 2002: (1) “Avoid the temperature reaching much above about 650°C in an oxidising atmosphere or much above about 750°C in a reducing atmosphere”; (2) “Wetting the clay with sea water (RYE, 1976) or adding a few percent of sodium chloride to the clay” (even 0.5% NaCl promotes a reaction between CaCO₃ and iron, which forms stable compounds at temperatures below 900°C-1000°C; LAIRD AND WORCESTER, 1956; BUTTERWORTH, 1956, quoted in STIMMELL ET AL., 1982, 222); (3) “Quenching the vessel, immediately after firing and whilst still red-hot, in cold water”; (4) Firing at temperatures exceeding 900°C let the free CaO combine with alumina and silica released by the thermal decomposition of clay minerals to form high temperature minerals such as diopside, gehlenite and anorthite (HEIMANN, 1989 141).

Firing method (open firing vs. kiln firing) and gran-
ulometry of the clay are important, resulting in varying the temperature of lime formation. Hence, the temperatures proposed here are only approximate.

#### 3.4.5.4 Oxidising firing of carbonate-rich clays

Appendix 7A shows the mineralogical associations published in the literature for oxidising firing of carbonate-rich clays.

BENGHEZAL (1994A) expressed that (002) and (003)-peaks of chlorite disappear at 550°C, whereas (001)-peak is lost at 700°C. These facts are in concordance with the observations of the other authors for who chlorite disappears between 650° and 700°C (TITE, 1995; BÉARAT, 1992 and JORNET ET AL., 1985).

For every author, kaolinite disappears below 500°C or around 550°C, except for HERZ AND GARRISON (1998, 263, 264): "750°C-850°C: (...) kaolinite and smectite begin to lose their characteristic crystalline structure. (...) 950-1100°C: The structure of most kaolinite and smectite is irreversibly lost."

Montmorillonite seems to have a very varied temperature of disappearance: 500°C (BENGHEZAL, 1994A) or 750°C in marls (MAGGETTI, 1986; MAGGETTI ET AL. 1984). PETERS AND IBERG (1978) studied a marl from the Molasse Basin of Switzerland and observed that montmorillonite starts to disappear at 650-700°C, with a rapid decrease of the mineral around 800-850°C and its loss at 950°C. HERZ AND GARRISON (1998) showed that smectites disappear around 950°-1100°C.

Illite disappears between 900°C (LETSCH AND NOLL, 1983) and over 1100°C (HERZ AND GARRISON, 1998). The detailed disappearance of (001), (002) and (110)-peaks is varying between 800°C and 1000°C as a function of the authors' experiments. In HERTLI ET AL. (1999), (001) peak of illite is well visible below 850°C; between 850°C and 950°C (001) peak of illite "has disappeared or is only present as small shoulder. The maximum temperature of 950°C can be determined through the presence of the illite (020) reflex. Missing illite is a sign that the temperature is above 950°C". CULTRONE ET AL. (2001, 631) wrote that over 1000°C, phyllosiliates have already disappeared in all clays, being transformed into sanidine and mullite plus a melt".

In HERZ AND GARRISON (1998, 263), "quartz inverts at 573°C from the alpha (low temperature) to the beta (high temperature) form, accompanied by a volume expansion of 2%". For many authors, quartz is lost at

1150°C and plagioclase is always present until over 1100°C.

K-feldspar disappears at 900°C (MAGGETTI, 1982), 1000°C (BÉARAT, 1992) or over 1100°C (JORNET ET AL., 1985; HERZ AND GARRISON, 1998). CULTRONE ET AL. (2001, 631) observed that "K-feldspar progressively disappears as temperature increase. It seems that low-temperature K-feldspar (microcline) is not stable at high temperature, therefore, it transforms into a high-temperature K-feldspar (i.e. sanidine) or reacts with lime to form anorthite". Moreover, TITE ET AL. (1982) show that the content in anorthite is maximum in CaO-rich clays if Ca is equal to 10% in clay containing fine-grained calcite, and if Ca is around 15-25% when calcite is present as inclusions.

Aragonite is lost below 500°C (ECHALLIER AND MÉRY, 1992), whereas dolomite disappears from 550°C (HEIMANN, 1989) to 800°C (CULTRONE ET AL., 2001).

Calcite turns to lime from 650°C (BÉARAT, 1992; BENGHEZAL, 1994A) to below 800°C (JORNET ET AL., 1985), and this latter is lost from 800°C (LETSCH AND NOLL, 1983) to 1100°C (JORNET ET AL., 1985). Several authors did not mention the disappearance of lime at high temperature (BÉARAT, 1992; BENGHEZAL, 1994A; ECHALLIER AND MÉRY, 1992; MAGGETTI, 1986; MAGGETTI ET AL. 1984). ECHALLIER AND MÉRY (1992) AND MAGGETTI ET AL. (1984, 173) resume the phenomenon well: "the transformation of calcite into lime begins slowly around 750°C, brutally accelerates between 800 and 850°C and achieves at 900°C. But when the ceramics are made of marls in which calcite is present as very small particles, the temperatures are often inferior". For CULTRONE ET AL. (2001, 628), calcite and dolomite "are fully transformed either into burnt lime (CaO) or into a mixture of burnt lime and periclase (MgO)" at 800°C. Finally, HEIMANN AND MAGGETTI (1981, 166) specify that the temperature of decarbonisation of calcite is strongly dependent on the particle size; quoting MACKENZIE (1957), some of the larger grains cause markedly delayed dissociation and will be preserved therefore at considerably higher temperature (up to 1050°C!).

BÉARAT (1992) described a presence of hematite below 800°C, with its loss at this temperature. For other authors, hematite appears at 750°C (or 820°C, TITE, 1995) and can disappear at 900°C (MURAD AND WAGNER, 1989) or not (BENGHEZAL, 1994A, for example). CULTRONE ET AL. (2001) observed an increase of hematite peaks over 1000°C.
Periclase appears at 700°C (BÉARAT, 1992). Gehlenite forms from 750°C (LETSCH AND NOLL, 1983) to 900°C (JORNET ET AL., 1985) and disappears respectively from 950°C to over 1100°C, or is still present over 1100°C (BÉARAT, 1992). CULTRONE ET AL. (2001), following the work of Maggetti, specify that “gehlenite starts to form at 800°C by grain-boundary reaction between CaO, Al₂O₃ and SiO₂, the first deriving from former carbonates and the later two from already dehydroxylised phyllosilicates”. Moreover, a direct correlation between amounts of CaCO3 and gehlenite was observed by STIMMELL ET AL. (1982, 222): “the relative peak heights of the gehlenite (211) interference at 2.85 Å against the calcite (102) interference at 3.86 Å” show a correlation coefficient of 0.79. TITE ET AL. (1982) specify that if Ca >25% in clay (hence, CaO > 35 %), gehlenite is present at 1100°C; if there is less Ca, gehlenite disappears around 1000°C. Gehlenite is often not described in ancient pottery sherds. HEIMANN (1989), HEIMANN AND MAGGETTI (1981), KÜPFER AND MAGGETTI (1978), MAGGETTI (1982) and MAGGETTI AND HEIMANN (1979), propose three different possibilities for that absence: (1) Because gehlenite is metastable, it tends to disappear at firing temperatures exceeding 950°C and forms anorthite by reaction with silica: very high firing temperatures or very long holding at maximum temperatures prevent its crystallisation ; (2) Gehlenite is often absent of well-processed clays with a small grain size, and is present when the same clay is used to manufacture coarse products; (3) Gehlenite is decomposed to calcite and zeolites by soil solution during burial in a humid climate, whereas it stays if the soil is dry.

MAGGETTI (1979) observed that the transformation from goethite present in pisoliths to hematite is done at 370°C.

Anorthite appears from 750°C (MURAD AND WAGNER, 1989) to around 900°C (PETERS AND IBERG, 1978; CULTRONE ET AL., 2001); it starts to form at the expenses of calcite and illite, plus quartz. Diopside and wollastonite respectively form at the dolomite-quartz interfaces and at the carbonate-quartz interfaces from 800°C (LETSCH AND NOLL, 1983; CULTRONE ET AL., 2001, 631). TITE ET AL. (1982) add that diopside or wollastonite crystallise whereas Ca is equal to 15-25% (CaO: 21-35%) in clay as fine-grained calcite and whereas Ca >25% (CaO >35%) in clay as calcite inclusions.

Sanidine and mullite respectively appear over
950°C and around 1000°C.

As shown on Appendix 7A, these differences of

temperatures cannot be put into relation with the min-
eralogy of the fired clay.

To resume the table A of Appendix 7, it is obvious
that the apparition and disappearance temperatures of
each mineral are strongly dependant on the clay com-
position: carbonate-rich clays differ a lot from one
place to another, depending on the geology, even in
one country. For example, a carbonate-rich clay con-
taining lots of illite will react differently than a kaoli-
nitic one. Hence, the stability of minerals should not
be taken from the literature between geological
regions. Authors have to make their own firing experi-
ments in order to appreciate the behaviour of the min-
erals present in the clay used in the studied potteries.

3.4.5.5 Oxidising firing of silicate-rich clays

Appendix 7B shows the mineralogical associations
published in the literature for oxidising firing of sili-
cate-rich clays.

BENGHEZAL (1994A, 1999) shows that (002) and (003)-peaks of chlorite disappear at 500°C, whereas (001)-peak stays until 600°-700°C. Other authors observed a lack of chlorite over 670° to 750°C. MAGGETTI (1979) quoted GRIM (1968) who measured at 550°C that chlorite had disappeared. MURAD AND WAGNER (1989) explained the wide variation of the minerals formed from fired chlorites: “Upon heating chlorites, the brucite sheet becomes dehydroxylised at 500-600°C whereas the silicate sheet becomes dehydroxylised at about 700-800°C. Heating low-iron chlorites to over 600°C leads to complete oxidation of iron (II), whereas iron (II) in iron-rich chlorites is only insignificantly oxidised. Depending upon the original chlorite composition and the firing atmosphere, a wide variety of heating products (olivine, spinel, hematite, cristobalite) can ensue when chlorites are fired.”

Kaolinite transforms, loosing their hydroxyl
groups, to an amorphous constituent called meta-kao-
linite between 350° and 500°C (MURAD AND WAGNER,
1989; HEIMANN AND FRANKLIN, 1980) and disappears
before 500°C (MURAD AND WAGNER, 1989) or around
550°C.

Vermiculite is lost before 500°C (MURAD AND WAGNER, 1989; PICOUET, 1997).

Montmorillonite disappears before 550°C for sev-
eral authors (PICOUET, 1997; MAGGETTI, 1993;
BENGHEZAL, 1994A), but is still present to 800° or
950°C for others (only (110)-peak?; MAGGETTI, 1982, 1986; MAGGETTI ET AL. 1984).

At 500° to 550°C, illite looses its hydroxyl groups, and retains a distorted structure for another several hundred degrees (HEIMANN AND FRANKLIN, 1980, 27). Illite, then, is lost from 850°C to 1050°C (MAGGETTI, 1982). When each peak – (001), (002), (110) – disappears is not clear in the literature. For example, BENGHEZAL (1990) observed (001) and (002)-peaks of illite disappear at 850°C and no illite left between 900° and 950°C. The explanation of CULTRONE ET AL. (2001), “only the diffraction peak at 10 Å, corresponding to a dehydroxylated illite-like phase, remains at 700°C. This peak intensity is reduced upon firing at higher temperature, till it disappears at ~900°C” is prevailing.

Muscovite undergoes a solid-state phase change into a mixture of mullite and K-feldspars at temperature ranging from 800 to 1000°C (CULTRONE ET AL., 2001, 630).

Quartz is still present at 1050°C (MAGGETTI, 1986; MAGGETTI ET AL. 1984) and even at 1150°C.

K-feldspar disappears at 1050°C; is transformed from microcline to sanidine over 1000°C (CULTRONE ET AL., 2001) or from low-microcline to intermediate microcline at 900°C (PICOUET, 1997). For BÉARAT (1992), it is always present. CULTRONE ET AL. (2001), quoting the work of various authors, show that the plagioclase increases its Ca-content (becomes more anorthite-rich) together with its main peak intensity as the temperature increases. As observed in PICOUET (1997), a phase appear by two peaks (2θ= 21.16° and 27.16°) between 900 and 1050°C. These peaks could be attributed to intermediate microcline. These two peaks are not new, but result of a displacement of peaks 20.98°2θ and 27.02°2θ, due to a change in its structure. The “low-microcline” is triclinic and becomes monoclinic with the elevation of temperature.

Plagioclase disappears from 850°C (BENGHEZAL, 1999) to 1050°C (MAGGETTI, 1993, 1995B) or is always present (MAGGETTI, 1986; MAGGETTI ET AL. 1984).

As observed under the microscope, amphibole disappears at 950°C (MAGGETTI, 1986; MAGGETTI ET AL. 1984) or not, only changing its colour (ECHALLIER AND MÉRY, 1992).

LETSCH AND NOLL (1983) show an increase of hematite between 500°C and 900°C, followed by a decrease over 900°C. Other authors observed the formation

of hematite from 600°C (BENGHEZAL, 1999) to 850°C (BÉARAT, 1992; MURAD AND WAGNER, 1989).

Dolomite is lost at 500°C (BENGHEZAL, 1994A) or 670°C (BÉARAT, 1992), whereas calcite disappears at 950°C (BENGHEZAL, 1994A).

Bixbyite disappears at 850°C (LETSCH AND NOLL, 1983) It is replaced by spinel if Mn*100/(Mn+Fe) = 2.3-57% and by spinel and braunite if the ratio is equal to 73-91% (LETSCH AND NOLL, 1983). Pyroxene is still present at 1150°C (MAGGETTI, 1986; MAGGETTI ET AL. 1984). Mayenite and braunite respectively appear at 774°C, (ECHALLIER AND MÉRY, 1992) and 850°C (LETSCH AND NOLL, 1983). This latter decreases over 900°C. The first forms from the breakdown of clay minerals and calcite and the second from the decomposition of bixbyite and illite in presence of manganese.

For every author, spinel forms between 850°C and 1000°C (PICOUET, 1997). Only MAGGETTI (1982) describes spinel between 500° and 700°C. Spinel crystallises if illite is predominant to kaolinite in the clay (TITE ET AL., 1982). These temperatures shall be taken with care, fact which was well explained in LETSCH AND NOLL (1983, 269): “A drop in the oxygen content of the kiln atmosphere to, say, 1% would result in the formation of spinel beginning at 722°C instead of at 873°C. [...] Moreover, since the manganese-oxide phase transformations proceed quite rapidly, this would explain why spinel can be found in antique sherds fired at relatively low temperatures. Once formed, spinel is essentially resistant to the reactive siliceous matrix developed through the decomposition of illite”. As explained in HEIMANN AND FRANKLIN (1980, 27), above 900°C, the meta-kaolinite and illite begin to crystallise into an Al-spinel.

Mullite forms from 800°C (MURAD AND WAGNER, 1989) to 1100°C (MAGGETTI, 1982). Mullite crystallises if kaolinite is predominant to illite in the clay (TITE ET AL., 1982). CULTRONE ET AL. (2001) specify that the intensity of the main diffraction peak of mullite (3.39 Å) increases over 900°C. Mullite and cristobalite are formed from the break down of the structure of meta-kaolinite. Some iron can substitute for aluminium in mullite and the rest will form hematite (MURAD AND WAGNER, 1989). HEIMANN AND FRANKLIN (1980) say that above 1000°C, spinel breaks down to form mullite.

Cristobalite appears from 800°C (MURAD AND WAGNER, 1989) to 1050°C (MAGGETTI, 1982), and ackermanite at 1058°C (ECHALLIER AND MÉRY, 1992).
In the table B of Appendix 7, the stability of the minerals is also strongly dependent on the clay composition: an illitic or illitic-montmorillonitic clay is quite different from a kaolinitic clay. Hence, the results presented in the literature shall be taken with care; they have to be used only if the geology of the studied area is similar to that of the literature.

### 3.4.5.6 Reducing firing of carbonate-rich clays

Appendix 7C shows the temperature of formation of the different minerals mentioned in the literature.

Quartz disappears at 1150°C. Plagioclase increases between 800°C and 1000°C (LETSCH AND NOLL, 1983). Chlorite and illite disappear at 700°C. Calcite disappears around 900°C. No lime is formed. Hematite is lost below 600°C, turning to magnetite, which appears at low temperatures in reducing conditions (around 700°C) and remains un-dissociated up to higher temperatures (MANIATIS ET AL., 1983). Magnetite is a typical mineral to show a firing in a reducing atmosphere (MAGGETTI, 1993); moreover, according to HEIMANN ET AL. (1980) the absence of magnetite in a CaO-rich ceramic points to strongly reducing conditions ($f_{O_2}$ less than $10^{-4}$ atm). Gehlenite forms at 850°C after the reaction of CaO with the $Al_2O_3$ and $SiO_2$ of the clay minerals and disappears at 950°C, replaced by diopside (MANIATIS ET AL., 1983; LETSCH AND NOLL, 1983). The results produce evidence that gehlenite accommodates ferric iron in its structure, probably in Al sites, and that the formation of this Fe-gehlenite phase is not inhibited by the reducing conditions (MANIATIS ET AL., 1983).

Wollastonite crystallises around 900°C, at the expense of $SiO_2$, which decreases in quantity, together with diopside. Hercynite is present around 1000°C, whereas hedenbergite appears at 1000°C. The lack of formation of fayalite and hercynite is probably due to the low iron content of the clay, whereas its presence indicates that strongly reducing conditions were obtained (MANIATIS ET AL., 1983).

Table C of Appendix 7 proves the few experiments proposed in the literature concerning reducing firings. As for oxidising firings, the forming and disappearing temperatures of minerals is strongly bound to the composition of the clay used. In this case however, the oxygen fugacity is a second very important parameter to care about. The results in the literature concerning reducing firings have to be used with very much care in other geological areas.

### 3.4.5.7 Reducing firing of silicate-rich clays

Appendix 7D, quartz, plagioclase, chlorite and illite behave as described for reducing firing in CaO-rich clays. Kaolinite and manganosite respectively disappear below 500°C and 750°C.

In $Fe_2O_3$-rich clay, hematite disappears below 600°C forming magnetite (LETSCH AND NOLL, 1983), whereas it appears at 800°C in MURAD AND WAGNER (1989).

Magnetite is lost at 900°C; its absence is explained by its poor crystallisation and small particle size in MANIATIS ET AL. (1983). Tephroite (formed from thin clay particles and manganosite), hercynite (crystallising from illite and magnetite), spessartine (replacing quartz grains), fayalite and iron (which presence indicates extremely strong reducing conditions) are respectively formed at 750°C, 850°C, 900°C and around 950°C for both last. Fayalite appears if Fe/Si < 50%, whereas iron is formed if the ratio is higher than 50% (LETSCH AND NOLL, 1983).

Around 1100°C, “the quartz grains are surrounded by glass and the small ones appear rounded, indicating their gradual fusion into the glass. No iron oxides are visible. Fayalite and cordierite have not been formed; the failure of this formation may be attributed to the high amount of $Al_2O_3$ present in this clay, which does not favour the formation of fayalite” (MANIATIS ET AL., 1983).

Table D of Appendix 7 is similar to table C, but moreover, kaolinitic clays have very different belongings from illitic and illitic-montmorillonitic clays. Hence, the results concerning kaolinitic clays should not be used for illitic clays. The results of table D shall also be used with very much care.

## 3.4.6 Firing temperatures: main results of previous studies on Swiss Neolithic ceramics

NUNGÄSSER AND MAGGETTI (1978) studied the ceramics of Burgäschisee (10 km SE of Solothurn) and observed illite and chlorite. Due to the presence of the latter, they suggest a firing temperature between 450°C and 500°C.

NUNGÄSSER ET AL. (1985) studied the ceramics of Twann: 80 ceramics are of the Cortaillod period (3840-
3530 BC) and 20 of the Horgen (3410-3070 BC). The firing temperature is around 400°C to 600°C in a reducing atmosphere.

KILKA (1999 193, 194) described 61 Neolithic to Iron-Age ceramics from Borscht (FL). 8% are fired under 700°C, 76% fired between 700 and 850°C, 13% around 850°C and 3% over 850°C.

SCHUBERT (1984A, 1984B, 1987) studied Neolithic ceramics (late Cortaillod and Horgen cultures) from Zürich Kleiner Hafner and suggests a firing temperature around 700°C to 800°C.

BENGHEZAL (1993, 1994A, 1994B) studied 194 samples from five Swiss late Neolithic sites (Auvernier, Portalban, St. Blaise, Vinelz and Sutz). These ceramics were fired in reducing atmosphere with an oxidising cooling or post-firing. 50% of the ceramics were fired between 500 and 650°C, 44% between 650 and 750°C and 6% around 800°C. The petrographical, mineralogical and chemical analyses demonstrate that thin and coarse ceramics cannot be distinguished and had the same firing temperatures (500°C-650°/750°C). She also studied French sites: in Chalain and Clairvaux the firing temperatures were not higher than 650°C, and around 750-800°C in Barrou and Charavines. DI PIERRO (2002) studied 128 samples from Portalban and St. Blaise (late Neolithic sites); he agrees with the results of BENGHEZAL (1993, 1994A, 1994B) concerning the firing temperatures.

In conclusion, there are three groups of firing temperatures: 450°C-600°C as defined by NUNGÄSSER AND MAGGETTI (1978) and NUNGÄSSER ET AL. (1985); 500°C-750°C defined by BENGHEZAL (1993, 1994A, 1994B) and DI PIERRO (2002) and 700°C-850°C defined by KILKA (1999) and SCHUBERT (1984A, 1984B,1987). These differences are less important than it can be thought: all are low temperatures in regard to Roman firings for example. Moreover, open firings induce a wide variation of temperatures during firing (see figure 3.7).

### 3.4.7 Discussion

Based on the literature and on experimental firings in oxidising atmosphere, mainly, the firing temperatures of ancient ceramics can only be approached indirectly. As presented here, minerals appear and disappear at known temperatures, governed by thermodynamic rules. Moreover, the results of the firing experiments

proposed in the literature should be used with caution because the clays of other sites are normally minera- logically and granulometrically different.

The firing atmosphere of ancient ceramics can be deduced by observing the colour of the sherds (if not contaminated) and assured by the reduction factor FeO / FeOtot (for details, see 6.5.2).

The mineralogical associations analysed by X-ray diffraction, the firing atmosphere and the literature permit to deduce a range of temperature in which the ceramics were fired. Unfortunately, this range is often broad (i.e. 300-500°C of variation) and often does not permit to determine neither the firing structure, nor the firing duration, nor the fuel used.

## 3.5 CONTAMINATION BY USE AND BURIAL

### 3.5.1 Introduction

Contamination group various phenomenons that modify archaeological remains during their deposition and/or use. It may strongly affect the composition of these objects. Large variation in the concentration of a component in a group of similar samples (with similar proportions of temper) is a strong indicator for contamination. Mobile elements (such as K and Na) can be leached and carried away, or transported and precipitated into the ceramic. The filling of cavities with Ca- and/or Mg-carbonates is frequent. CaO and P₂O₅ are the more susceptible to change with contamination and should be used with care.

The more stable and reliable chemical elements are SiO₂, Al₂O₃, Fe₂O₃ and TiO₂. At this list, MgO, Na₂O, K₂O, Li, Rb and Cs can be added in the case of CaO-poor clays (BÉARAT AND DUFOURNIER, 1994A).

### 3.5.2 Secondary montmorillonitisation

The presence of expandable phyllosilicates (smectites) such as montmorillonite or mixed-layer minerals in low-fired ancient sherds is explained as a rehydration during burial of primary smectites, which were partially destroyed during firing (MAGGETTI AND SCHWAB, 1982). Montmorillonite is obviously a secondary mineral, because a mineral containing a smectitic phase loses its water layer below 300°, and all the ceramics were
fired higher than 400°C-500°C (more than the lower temperature proposed in the literature for Neolithic firings, NUNGÄSSER AND MAGGETTI, 1978; MAGGETTI, 1979; NUNGÄSSER ET AL., 1985). However, X-Ray diffractograms of Neolithic ceramics frequently show a broad peak between 5 and 10°2θ. Detection by glycolation techniques show a mixed-layer phase containing montmorillonite. This broad peak, which is reduced to a single peak of illite or split into an illite and chlorite basal peak if fired to 200-300°C, is caused by very fine grained clay particles of a mixed layer type (probably chlorite-illite). The disappearance of this peak at 300° shows that these mixed layers were formed during burial (MAGGETTI, 1982).

Even if montmorillonites are fired to 600°C, they can regain their water interlayers during burial (NUNGÄSSER AND MAGGETTI, 1978).

### 3.5.3 Phosphorus

Phosphorus is the most common element affected by contamination. The bulk $P_2O_5$ concentration of most of the clays varies between 0.1 and 0.5 wt.% (KORITNIG, 1978). Higher phosphorous contents than these values in ceramics have been frequently detected and described (see for example BÉARAT 1990, 1992; BENGHEZAL, 1990; DUFOURNIER, 1976; DUMA, 1972; FREESTONE ET AL., 1985; HEIMANN AND MAGGETTI, 1981; LEMOINE AND PICON, 1982; MAGGETTI, 1980, 1982; MORZADEC, 1991; PICON, 1976; WALTER AND BESNUS, 1989). Such high values may have different origins.

First, high contents of $P_2O_5$ can be related to a treatment of the clay before firing; substances rich in phosphorus such as urine or faecal material can increase the plastic behaviour of the clay (ROTTLÄNDER, 1981-1983; MAGGETTI, 2001).

Second, the presence of bone fragments as temper may be a cause for high phosphorus contents (BONZON, 2004B).

These two first cases are not considered as contamination in opposite to the next points.

Third, the daily use of the ceramics was only rarely studied (BÉARAT, 1990; BÉARAT AND DUFOURNIER, 1994A, 1994B; DUMA, 1972; FABBRI ET AL., 1994). In BÉARAT AND DUFOURNIER (1994A, 1994B), the ceramics are put in contact with milk, wine and urine and their belonging is studied. They show an increase of

$P_2O_5$-content after holding and cooking of phosphorous-rich products such as milk and wine. The phosphorous is adsorbed on pore walls or substituted into clay minerals. At the end of the experiments, the proportions of $P_2O_5$, CaO, MgO, $K_2O$, MnO, $Na_2O$ and loss on ignition (LOI) showed significant variations. They conclude that the fixation of $P_2O_5$ is better if the clay is CaO-rich, if the temperature of the environment is high, if the time of contact is long, if the ceramic is used during a long time, and if the ceramics are fired around 600°C to 800°C (DUMA, 1972; BÉARAT AND DUFOURNIER, 1994B).

Fourth, DUMA (1972) put into relation the high content of phosphorus with the use of the vessel as a funeral urn, implying after a time the dissolution of bone and the precipitation of the phosphorus into the ceramic.

Fifth, the enrichment in phosphorus is frequently related to the burial environment (BÉARAT, 1990; FREESTONE ET AL., 1985; LEMOINE AND PICON, 1982; MORZADEC, 1991). The leaching of certain elements is another mechanism to increase the concentration of the remaining elements. HEIMANN AND MAGGETTI (1981) studied calcareous ceramics after firing and burial. They evidenced possible modifications in the concentrations of the elements Ca, Fe, Mn, Na and K during burial. LEMOINE AND PICON (1982) experimentally showed that high phosphorous values in their sherds are directly correlated with the leaching of mobile elements such as K, Na, Si and Mg. Hence, a negative correlation between mobile elements and P may indicate chemical modifications due to leaching. MAGGETTI (1994) and COLLOMB AND MAGGETTI (1996) explained the post-depositional phenomena as follows: "Lightly fired pottery consists of a large proportion of decomposed clay minerals, of which the amorphous breakdown products are highly reactive. In the ground they react relatively quickly to outside influences and following reaction processes may be listed: extraction of sherd material (dissolution phenomena); deposition of minerals in pores and voids (cementation phenomena); decomposition of existing primary or firing minerals to secondary minerals" (MAGGETTI, 1994, 31).

### 3.5.4 Others

Diagenetic changes during burial are an especially serious problem for low-temperature ceramics. Potteries fired below 700°C are generally very porous, allowing easy access for outside solutions. The porous-
ity is due to the manufacturing and firing process, the
chemistry and mineralogy of the starting material, and
the loss of outburning substances. Dissolution and
neocristallisation will take place: deposition in pore
spaces and replacement of primary minerals by sec-
ondary carbonates (calcite; MAGGETTI AND KAHR,
1981), hydrates (hydration of hematite to goethite;
ENRIQUEZ ET AL., 1979), oxides, hydrosilicates (zeo-
lites, clay minerals), and sulphates (gypsum; COURTOIS,
1976) (MAGGETTI, 1982; HERZ AND GARRISON, 1998).

Secondary calcite results either from a migration of
carbonatic solutions from the ground during burial and
deposits into porosity or, if the firing process is too
rapid or the maximum temperature too low, the new
formed lime has no time to react with the silicates and
re-carbonates during the cooling or the burial
(MAGGETTI, 1982; ECHALLIER, 1984). This can induce
the lime-popping phenomenon described before.

Contamination with barium is less frequent (PICON,
1985; PICON AND LE MIÈRE, 1987; BENGHEZAL, 1990).

Chlorides sometimes alter deeply the ceramics that
become very light and non-resistant. Variations of
temperature, such as frost, also modify the sherds.
Hence, sometimes, only the microscopic analysis per-
mits to distinguish between altered and fresh sherds
(CAMPS, 1990).

**3.5.5 Discussion**

Contamination implies severe problems when ana-
lysing ceramics. A chemical analysis can be totally
modified because a sample was contaminated. In such
cases, mixing "clean" and contaminated sherds leads
to wrong grouping, and, hence, wrong geological attri-
butions. Hence, the sherds have to be well described
before being analysed. A piece of sherd is always kept
until the end of the study to assure the observations if
necessary.
# 4 - GENERALITIES CONCERNING THIS ARCHAOMETRICAL STUDY

## 4.1 SAMPLING STRATEGY

### 4.1.1 Non-ceramic material from Arbon Bleiche 3

1 loom weight (of 23 discovered) and 11 cob fragments were studied. The cobs were analysed in order to identify the raw material used to build the house walls and to compare it with the clay used for pottery.

### 4.1.2 Clays and rocks

12 clays and around 60 rocks were collected in the region of Arbon to determine the quality and the mineralogy and chemistry of the resources (clay and temper) that were available in the Neolithic.

The local clays were collected within a 2.5 kilometres wide perimeter around the site (Fig. 2.11). This 2.5 km perimeter was chosen because it included the Rhine morainic deposits of the vicinity of Arbon and the molassic deposits present in the hills of the neighbourhood, which are the main geological resources of the surroundings of Arbon Bleiche 3.

As visible on Fig. 2.11, JB303, JB304 and JB305 were collected in the Würm moraines whereas JB306 and JB307 were collected in the Molasse. JB300, JB301, JB302, JB308 and JB309 seem to have been collected in the Quaternary alluviums. However, JB300, JB301 and JB302 were sampled at the level of the water of the small stream, i.e. under about 3 meters alluviums, in the Würm moraines. JB308 and JB309 were sampled when a little dam reservoir was being digged and the deep sediments deposited on its bor-

ders; geologically, these sediments correspond to molassic deposits. Even if JB310 seems to come from the Würm moraines on Fig. 2.11, a little molassic deposit was observed in this place and the sample came from it. Hence, even if Fig. 2.11 does not show precisely what the sampled clays are, JB300 – JB305 were collected in the Würm moraines whereas JB306 – JB310 were sampled in the Molasse beds.

### 4.1.3 Ceramics from Arbon Bleiche 3

At least one sherd, and frequently three sherds were taken from every studied pottery. Among the about 3000 vessels (DE CAPITANI 2002, 139) 153 potteries were analysed (Appendix 1), at different dates, in collaboration with A. de Capitani:

60 sherds of Pfyn / Horgen pots of 352 (17%). This sampling of pots was sufficient, because the results were repetitive. Hence, 15 Pfyn / Horgen pots first selected were not analysed (JB156, JB161, JB168, JB170, JB176, JB184, JB191 to JB199).

93 special forms (of 135, thus 69%). This sampling was maximised because the results were not repetitive; the other special forms could not be analysed, since it was not possible to destroy these unique potteries by sampling. Two undetermined special forms were only partially analysed because the sherds were too small (JB172, JB188).

10 spindle whorls (of more than 400 found in the excavation).
### 4.1.4 Ceramics from the western Carpathian Basin

14 ceramic sherds from the western Carpathian Basin were investigated; they came from Austria (site Mödling “Jennyberg”, 5 samples); Slovakia (Zlkovce, 5 samples) and the Czech Republic (Náměšť na Hané, 4 samples). The sherds were chosen by de Capitani and are typical Boleráz forms. The archaeological description of these samples is found in DE CAPITANI (2002, 214). These samples come from the region where Boleráz' typology was first defined by the archaeologists. Hence, they have to be correlated with the special forms of Boleráz-pottery from Arbon Bleiche 3.

## 4.2 METHODOLOGY

### 4.2.1 Ceramics and non-ceramic material

#### 4.2.1.1 Thin sections

First, a picture of every sherd was taken, before the latter being sawed, permitting to prepare a thin section. All the sherds were cut perpendicular to the lip and parallel to the vertical axis of the pottery. In the case of body fragments without clear orientation, the section was cut perpendicular to the long axis of the sherd. The majority of the thin sections were then comparable. One thin section was made from every archaeological object by J.-P. Bourqui.

#### 4.2.1.2 Qualitative study of the thin sections

Thin sections were qualitatively studied under a Leitz Laborlux polarising light microscope to define petrographical groups by observing the nature of the matrix, of the non plastic inclusions and their structure. The study of the thin sections was carried out without knowing to which typological group the studied sample belongs.

BISHOP ET AL. (1982), quoted in BARNETT (1990) expresses that a “successful petrographical analysis of pottery to determine production location requires that ceramic assemblage be made from clays that are found in an area with diverse geologic resources, and contain a significant amount of coarse inclusions in the paste”. The ceramics from Arbon Bleiche 3 fulfils both of these criteria: the ceramics have typically coarse

pastes, and contain detrital and added particles up to 1 cm Ø that are geographically unique, derived from granite, gabbro, chert and rhyolite of the eastern Alps and deposited in the Rhine Basin.

In this work, the qualitative observation of one thin section pro sample is assumed to be representative of individual ceramics. Petrographical analysis is used because it can classify individual non-plastic grains of clay and pottery samples, even though the categories are descriptive. These classifications include mineralogical and petrographical compositions, size and angularity of the grains and are not significantly affected by chemical and mineralogical changes that can occur during firing and burial. Petrographical analysis can also identify the effects of modification of the clay by ancient potters such as tempering (MAGGETTI, 1982, 1994; HOWARD, 1982; RYE, 1981; BARNETT, 1991).

The mineralogical taxonomy established for angularity by PETTIJOHN (1957) was used to describe the grains (angular, sub-angular, sub-rounded, rounded). As proposed in BARNETT (1991), angularity and size ranges for each mineralogical group are first established for the clay samples. These are then compared on an individual basis to vessel samples. Once added components are identified, they are distributed in various petrographical groups.

The problem of provenance of the sherds bound to their temper content observed in thin section was studied as described in MAGGETTI (1994, 26).

The forming technique of all the ceramics was studied on the thin sections and on the cut sections of the sherds.

#### 4.2.1.3 Quantitative study of the thin sections

The quantitative measurements of the temper (vol.%) were done on all the samples with the help of the “Spots before the eyes” method of MATTHEW (1991). Another quantitative analysis on 20 thin sections was made with a Swift Automatic Point Counter (Swift and Son, London). This latter is fixed on the microscope, permitting a 0.33 mm movement of the thin section for each impulse. The mineral on the intersection of the reticules was taken into account. The number of counted points varied around 1000 points. The integrated surface was about 108.5 mm². We followed the principles given in FREESTONE (1991, 403, 405) to decide how to point-count the thin sections:
"The accuracy and precision of a point count measurement depends on a number of factors, in particular the number of points counted (the more the better), the spacing between the points of the grid (ideally greater than the mean diameter of the particles being measured) and the proportion of the pace being measured (measurements of an abundant component will be relatively more precise than those of a minor component). These considerations indicate that if a component is actually present as 5% of the inclusions, then to state with 95% confidence that its concentration lies in the range 2.5% - 7.5% requires a total of 300 grains to be counted (GALEHOUSE, 1971). Thus, for a ceramic with 20% sand inclusions, 1500 point would have to be recorded to obtain such a level of precision. For components present in lower proportions, the requirements of the measurement are even more demanding. A point of contention is that of deciding which tapes of grains are to be measured; some authors advocate measurement of all non-plastic grains in a section whereas others exclude certain categories. The significance of measurements on very fine grains is unclear and many analysts do not measure below 20 – 30 µm".

SCHUBERT (1986, 194) expresses some problems related on thin sections measurements: The point-counting results do not mean, however, "that the sherd (and the slice thereof) is really representative of the whole vessel of coarse ware pottery".

THUESEN ET AL. (1989, 277) made a blind test to evaluate visual sorting of thin sections (such as the "Spots before the eyes" method of MATTHEW, 1991) by three persons. "The test showed a successful score between 78 and 94% for three persons, the actual fail sorting less than 5% in each case. Hence, the method is suitable for a general fabric classification".

This first approximation was then correlated with point-counting measurements (Point-counter Swift, London) permitting to assess the percentage of temper, of matrix and of porosity in the thin sections (MIDDLETON ET AL., 1985). As the differences between these two methods were less than 10 vol.%, the "Spots before the eyes" method was validated and used for the rest of the thin sections (validation method as defined in NUNGÄSSER ET AL., 1985).

20 thin sections were analysed on a coarse tempered pot (BONZON-FREUDIGER, 2005) in order to test the representativity of the sampling and we have to admit that the size of the sections is too small to get representative results from a single sample. In such coarse ceramics, 4 thin sections are necessary to have

a good estimation of the percentage of temper used. Hence, the results of the quantitative measurements of the temper described before have to be taken as useful information, but not at all as a precise quantity.

#### 4.2.1.4 X-ray diffraction

X-ray diffraction (XRD) was carried out on every sample, except those of the western Carpathian Basin, to identify mineralogical groups. After the removal of the possibly contaminated external and internal surfaces with a diamond saw, the samples were powered in a tungsten carbide mill. About 10 to 50 g of the coarse ceramics were ground. About 10 g of the fine ceramics were used when possible; if not, the minimum sample weight was 3 g. X-ray diffraction was carried out using a Philips PW 1800 diffractometer (CuKα, 2-65 °2θ, PC-APD and X-Pert software).

#### 4.2.1.5 X-ray fluorescence

On every sample geochemical analyses (XRF) were also made. The same powder was used as for XRD. Analyses were performed by Prof. G. Galetti on glassy tablets for major and trace elements. Those tablets were prepared by O. Marbacher with about 3 g powder dried for minimum 6 hours at 110°C and charred for one hour at 1000°C. The loss of ignition (LOI) was calculated from the weight of each sample after each step. 0.700 g of charred powder was mixed with 0.350 g of lithium fluoride and 6.650 g of lithium tetraborate. This mixture was put into a platinum crucible and melt at 1150°C for 10 min (Philips Perl X-2). Major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) and trace elements (Ba, Cr, Cu, Nb, Ni, Pb, Rb, Sr, V, Y, Zn, Zr) were analysed using X-ray fluorescence (Philips PW 2400). Calibration of major and trace elements were made on 59 standards. For analytical reproducibility and detection limits, see GALETTI (1994) and GIACOMINI (2001).

23 major elements (SiO₂, TiO₂, Al₂O₃, Fe₂O₃, FeO, MnO, MgO, CaO, Na₂O, K₂O and P₂O₅ expressed in weight percents) and traces (Ba, Cr, Cu, Nb, Ni, Pb, Rb, Sr, V, Y, Zn and Zr expressed in parts per million) were analysed for each sample in the laboratory of mineralogy. All these elements except FeO were used for the statistical treatment, for each analysed sample. FeO was not used, because it was not measured for every sample and because it depends on the firing atmosphere.
### 4.2.1.6 Statistics

The high number of X-ray fluorescence data made a statistical treatment of the results possible. Only for the ceramics, 163 samples were analysed and the results for each sample are presented as 23 chemical elements (major elements and traces). These elements are considered as statistical variables. The statistical analyses of the chemical data were made with the program SPSS, version 11.0. The statistical methodology used is proposed by BAXTER (1992; 1994A; 1994b; 1995; 1999; 2001A; 2001B; 2003); BOCQUET (1995); LE MAITRE (1982) and PICON (1984; 1992).

The presence of bone temper lowers the SiO₂ and Na₂O bulk concentrations relative to the other ceramics. In order to eliminate the influence of the bone temper and to compare the silicate part of the bone-tempered pottery with the other samples, the analyses were recalculated. The phosphate content was reduced to the average concentration of all other ceramics (mean: 0.23 wt.%) using a ratio for CaO / P₂O₅ of 1.33, a value determined by microprobe analyses of the apatite, the main constituent of the bone (BONZON, 2004B).

Before performing the analysis, all the chemical elements are standardized in order to put the major elements (in wt.%) and the trace elements (in ppm) at the same scale. The standardisation transforms the variables (chemical elements) to centred reduced variables. No log transformation was used. The standardised values were used for all the methods described further.

The similarity coefficient is then calculated: "Groups of neighbouring points in space are called clusters and are thought to represent the composition of a certain place. A similarity coefficient, e.g. the simple mean interpoint Euclidian distance between two points in this hyperspace is chosen. The nearer the points in space, the more similar they are in composition" (MOMMSEN ET AL., 1988, 48). The similarity coefficient is calculated for each pair of samples using average linkage between groups. When all the samples are clustered, the results are presented on a dendrogram that shows at which level the samples clustered together. The later two groups of samples are fused, the more dissimilar they are.

Principal component analysis (PCA) is a mathematical transformation from a matrix of n data and m variables to a new matrix of m new variables obtained by linear combination of the first variables. This method permits to reveal the existing structure between the variables and shows the proximity of the samples, hence, it

is possible to discern groups in the multivariate dimensions. PCA permits to reduce the number of variables keeping the maximum of variance. PCA was used in this work to visualise the distribution of the samples as a function of the 22 chemical variables, in order to recognise if different chemical groups can be separated.

Discriminant analysis (DA) is a statistical treatment in which discriminant factors are calculated in order to maximise the chemical differences of pre-established groups in the data set. If the DA finds a significant distinction between groups, these are used as reference to classify the archaeological samples of uncertain source. DA is frequently used to correlate ceramics from one site with groups of defined workshops, which permit to attribute an origin for a ceramic.

The Mahalanobis distance is often used in archaeometry to observe the appertaining of ceramics to a predefined group. This distance is a measure of how much the value of a variable of one sample differs from the average of all samples for a specific reference group. The greater the distance, the lower the probability for one sample to belong to a group defined by other samples. This method is one of the most sensitive, and permits to detect very small compositional differences between groups (PICON AND LE MIÈRE, 1987). SCHMID ET AL. (1999) observed that the chemical homogeneity of samples is demonstrated by the normal distribution of the samples in the histogram of Mahalanobis distances. WOLF (1999) confirms the results of SCHMITT (1998) that the Mahalanobis distance of a given sample seems to depend only little on the proportion of non-plastic inclusions.

### 4.2.1.7 FeO

FeO content was determined on samples JB001 to JB154 with the dipiridil method (LANGE AND VEJDELEK, 1980; BENGHEZAL, 1994A): 0.05 g of dry powder was put into a 2 ml acid solution (HF: H₂SO₄ 1:1). The solution was evaporated in a boiling water bath for 45 min. The residue was added to 50 ml buffer solution, then distilled water was added up to 500 ml. FeO was analysed with a Philips Pye Unicam PU 8650 (528 nm spectrophotometer). For standard preparation, see ZANCO (1999, 12). (Relative error for FeO: 0.04%, detection limit: 0.3 wt.%).

### 4.2.1.8 CO₂ and H₂O

CO₂ and H₂O were analysed respectively between
600°-1000°C and 20°-1000°C with a multiphase carbon determinator (Leco RC 412). The detection time was of 300 sec. (relative error for C: 3.5%, detection limit: 0.08 wt.%; relative error for H₂O: 12%, detection limit: 0.1 wt.%). CO₂ and H₂O were only measured on JB001 to JB154. These determinations were not performed on the other samples because the results were repeating themselves and the range of variation for quite all the ceramics was determined.

#### 4.2.1.9 Scanning electron microscope

Scanning electron microscope was used to take secondary electron images of bone fragments used as temper in some ceramics. The investigations were made on polished sections covered with carbon. A JEOL JSM-840A LGS microscope was used, operated at 15 kV.

#### 4.2.1.10 Electron microprobe

Electron microprobe was used to determine the bone temper. Analyses were performed at the Institute of Geology of the University of Bern with a Cameca SX50 instrument (15 kV, 20 nA, about 1µm electron beam diameter). Ca, P, F and Cl were measured on about 100 points on JB020 and JB069 bone fragments. To convert percent counts into oxides, the PAP program of Cameca was used.

#### 4.2.1.11 Nota Bene

All these methods were used as defined in DI PIERRO (2002), GIACOMINI (2001), PICOUET (1997) and ZANCO (1999). The preparations and measurements were all made at the Mineralogy and Petrography Laboratory of the University of Fribourg, except those of the microprobe.

### 4.2.2 Clays

#### 4.2.2.1 Briquettes and thin sections

In Fribourg, 8.1 x 4.1 x 1.2 cm briquettes of local clays were made and fired in an electric oven in oxidising atmosphere between 500°C and 1000°C. The elevation of temperature was of 100°C per hour. Temperatures were held constant for one hour at peak temperature to let new minerals form; then the oven cooled naturally down. Thin sections of every briquette were studied with a petrographical microscope.

The evolution of the mineralogy during the experiments was identified by X-ray diffraction.

#### 4.2.2.2 Granulometry

Laser granulometry was made on a Fritsch Particle Sizer Analysette 22 at the Institute of Mineralogy and Petrography of the University of Lausanne, under the direction of Dr. P. Thélin.

#### 4.2.2.3 X-ray diffraction

X-ray diffraction was made on each clay as described higher. Then, the argillaceous minerals were studied in two different granulometric fractions: < 2 µm and 2-16 µm. The clays collected in the neighbourhood of Arbon were mixed with demineralised water and were decarbonated. The needed fraction was separated by decantation and centrifugation. Each fraction was put on three different sections: one was not treated; one was glycolated during one night, which makes the clays swell, and the last one was heated at 550°C for one hour. The sections were analysed on a Philips Rigaku diffractometer (CuKα, 40 kV, 30 mA, 1-35 °2θ, NEWMOD software). This latter measurement was done at the Institute of Mineralogy and Petrography of the University of Lausanne, under the direction of Dr. P. Thélin.

#### 4.2.2.4 X-ray fluorescence

X-ray fluorescence was made on each clay as described higher.

## 4.3 TERMINOLOGY

The archaeological description of all samples (even the sherds from the western Carpathian Basin), their attribution to the typological groups together with the geographical coordinates at which the sherds were found in the excavation are described in DE CAPITANI (2002) and in Appendix 1.

### 4.3.1 Non-ceramic material

In Arbon Bleiche 3, 11 samples of cob fragments and one loom weight were not voluntarily fired before
being used, and were therefore considered as non-ceramic material.

## 4.3.2 Ceramics and potteries

In contrast, the ceramics are all the samples fired. Only the ceramic containers or vessels are named potteries. In Arbon Bleiche 3, the group is composed of 163 sherds of potteries and spindle whorls. From a macroscopic point of view, some Pfyn / Horgen pots are covered with barbotine. This latter is defined as a mixture of clay, temper and water put together on the outer surface of the pots (Fig. 4.1).

## 4.3.3 Matrix, non-plastic or natural inclusions and temper

The thin sections of Arbon-Bleiche 3 and those of the western Carpathian Basin were studied as shown on Fig. 4.2 with the following terminology: the samples are composed of a matrix (fired fine natural clay material) and non-plastic inclusions. These latter can come

from the natural clay, they are then natural inclusions, or can be added by the potter and are named temper.

### 4.3.3.1 Matrix typology

Two types of matrix are observed: Silicate-rich matrix: no optically visible grains of carbonate in the matrix, which is constituted mostly of silicates (argillaceous minerals, quartz, feldspars).

Carbonate-rich matrix: presence of micro-grains of carbonate in the matrix.

The proportion of matrix and natural inclusions defines two categories (modified from NUNGÄSSER ET AL., 1985; MAGGETTI, 1982 and BENGHEZAL, 1994A): Natural inclusions: < 5 vol.-%: inclusion-poor matrix Natural inclusions: > 5 vol.-%: inclusion-rich matrix

The matrix can contain natural inclusions as clay pellets and ARF (argillaceous rock fragments) (WHITBREAD, 1986). The differentiation between grog and argillaceous rock fragment (ARFs) followed the work of WHITBREAD (1986) and CUOMO DI CAPRIO AND VAUGHAN (1993). Iron oxide nodules are also natural inclusions.

<figure><img src="image_25.png" /><figcaption>**Figure 4.1:** Barbotine covering a Pfyn/Horgen pot. (DE CAPITANI, 2002, fig. 217; picture AATG, D. Steiner).</figcaption></figure>

<figure><img src="image_26.png" /><figcaption>**Figure 4.3:** A: Hiatal distribution of inclusions in a thin section: large grains are temper; B: serial distribution of the inclusions, which are possibly all natural (NUNGÄSSER AND MAGGETTI, 1978).</figcaption></figure>

<table><caption>**Figure 4.2:** What has to be described in a petrographical thin section</caption><thead><tr><th colspan="2">Matrix<br>vol.%</th><th colspan="5">Non-plastic inclusions<br>vol.%</th></tr><tr><th colspan="2">Clay minerals<br>vol.%</th><th colspan="2">Natural inclusions<br>vol.%</th><th colspan="3">Temper<br>vol.%</th></tr><tr><th>Silicate-<br>rich matrix</th><th>Carbonate-<br>rich matrix</th><th>Minerals<br>(quartz, micas,<br>feldspaths....)<br>vol.%</th><th>Fossils etc....<br>vol.%</th><th>ARF, clay pellets,<br>iron oxides, etc....<br>vol.%</th><th colspan="2">Rocks<br>vol.%</th></tr><tr><th></th><th></th><th></th><th></th><th></th><th>Granite<br>vol.%</th><th>Rhyolite<br>vol.%</th><th>Gabbro etc....<br>vol.%</th></tr></thead><tbody></tbody></table>
#### 4.3.3.2 Temper typology

The temper is sometimes hard to separate from the natural inclusions. MAGGETTI (1982, 130-131) noticed five principal criteria to identify temper:

(1) Calcite fragments. The presence of fresh rhomboedric calcite crush fragments with angular, sharp outlines is possible only if the ancient potters used crushed calcite; naturally present calcite would be very fine grained owing to the splitting behaviour of calcite and would also have rounded edges because of transport by water during the deposition of the clay.

(2) Fired clay. Fired clay, too, is an indication of artificially added temper and can be recognized – with respect to the embedding sherd – by differing colour, mineralogical composition, or texture (MAGGETTI, 1979)

(3) Organic material. Addition of straw, etc., was also frequently used by ancient potters and can be identified by the presence of abnormally high and coarse porosity and/or relicts of organic matter, often as black carbonaceous substance.

(4) Shape of the fragments. Angular fragments with sharp edges are often an indication that crushed material has been used (MARRO, 1978)". However, some alpine clay can also have angular quartz grains as natural inclusions, due to the short distance of transport that does not allow a rounding of the grains.

(5) "Granulometry. The presence of two populations of grain sizes (hiatal structure) is also an indication that coarser particles were added artificially (NUNGÄSSER AND MAGGETTI, 1978)". If the distribution is hiatal (Fig. 4.3A), the coarse grains are added temper and if it is serial (Fig. 4.3B), all grains are natural inclusions (NUNGÄSSER AND MAGGETTI, 1978). KILKA (1987, 1992) and KILKA AND GALETTI (1994) measure the size of grains and show the result in a histogram.

The local clays from Arbon Bleiche 3 have natural inclusions with a diameter normally below 0.5 mm, and rarely bigger than 1 mm. For that reason, we have defined the temper being all the grains above 0.5 mm of diameter in assumed locally made ceramics.

The temper is separated into three groups: fine temper is particles from 0.5 to 1 mm of diameter; medium temper, between 1 and 3 mm; and coarse temper, bigger than 3 mm. These classes are also used in DE CAPITANI (2002).

### 4.3.4 Reference groups

Several reference groups for Neolithic ceramics were defined in the Institute of Mineralogy and Petrography of Fribourg. MAGGETTI & GALETTI (1981) wrote: "A reference group is defined by a number of physical and chemical analyses statistically sufficient from an archaeological material obviously local. It can be a well defined ceramic typology (terra sigillata), a particular workshop (its own production), many workshops of a same region, or a group of sherds coming from one archaeological excavation, without a known production workshop." BÉARAT (1992) precised that "A reference group establishes when a ceramic whole is mineralogically and chemically homogeneous and refers to a distinct clay or to a place of production."

## 4.4 REPRESENTATIVENESS OF THE DATA

BONZON-FREUDIGER (2005) studied 20 sherds of a large Neolithic Pfyn / Horgen pot (see Appendix 12). She proves that the quantitative results extracted from X-ray diffraction and X-ray fluorescence analyses are representative for the whole ceramic, instead of the observation of one thin section per pottery.

After SCHNEIDER (1978), FREESTONE (1999, 114) says that "where groups are established on the basis of statistical analysis of quantitative [chemical] data, then the minimum size of a group to ensure that it is valid may well be 10 or more". In this work, the main groups contain enough ceramics to be representative. The samples of small petrographical groups (AII, AIII, AVI, BI, BII, BIII, CI, CII) are considered as exceptions. The use of statistics on archaeometrical studies is frequent, because the element concentration values of each sherd gives indications on the raw materials used to manufacture the ceramics. "Sherds with similar composition are thought to be produced by the same "recipe" in a specific pottery workshop using a clay bed in its neighbourhood. The composition data of pottery therefore allow provenance studies." (MOMMSEN ET AL., 1988, 47). Hence, sherds produced in different geological regions should show distinct chemistry. Only some of the elements can partly overlap. As specified in PICON (1992, 11), chemical resemblances in clay exploitation sites from different geological context only constitute a minor risk.
# 5 - ARCHAOMETRICAL RESULTS CONCERNING THE NON-CERAMIC MATERIAL: THE 12 SAMPLES OF LOOM WEIGHT AND COB FRAGMENTS FROM ARBON BLEICHE 3

## 5.1 MACROSCOPIC DESCRIPTION

The analysed one loom weight and 11 cob fragments consist of inclusion-rich clay made of a homogeneous carbonate-rich matrix, as revealed by the HCl reaction. All the samples are beige. Only on their external surfaces black marks are present, probably remains of the burning of the village at the end of the settlement phase.

## 5.2 PETROGRAPHICAL STUDY

All samples (loom weight, tempered and cob fragments, not tempered) entirely form the petrographic group CIII. This group is composed of an inclusion-rich and carbonate-rich matrix (Table 5.1, Appendix 3).

The non-plastic inclusions in the samples are of various sizes (<0.01–0.5 mm), various proportions (10–50 vol.%) and of various shapes (small ones: sub-rounded, big ones: sub-angular to angular). They are pieces of amphibolite, calcite, granite, or amphiboles. The loom weight (JB121) is tempered with organic material (straw, grass, hair, etc.) in opposition with the cob fragments, which are not tempered with such material (Fig. 5.1A). The vegetal fragments appear as carbonised black cells network. Textile and vegetal elements, such as straw, grass, hairs or ropes let long and thin open traces resulting from their charring (COURTOIS, 1976).

JB122 and JB123 show banded homogenous areas

containing more (40 vol.%, 0.02 – 0.5 mm, angular) or less (2 vol.%, 0.02 – 0.1 mm, rounded) quartz grains as natural inclusions. JB122 contains a few broken shells (~2 vol.%). JB124, JB130 and JB132 show one fragment of sub-angular to angular bone (respectively 0.5 mm, 0.1 mm and 0.25 mm long).

## 5.3 MINERALOGICAL STUDY

The organic matter, present as temper in the loom weight, is still visible on thin section (Fig. 5.1A) and not replaced by a hole, as it would be after firing. The mineralogy of the cobs cannot be distinguished from that of the analysed actual calcareous clays of the surroundings of Arbon. Apart from the minerals often present in clays (montmorillonite, kaolinite...), chlorite and calcite are still present, which tend to prove an absence of firing before the use of the cobs and the loom weight.

## 5.4 FIRING?

All 12 samples contain illite, quartz, plagioclases and potassic feldspars, but the proportion of calcite is higher or equal to the proportion of quartz (Appendix 2). They form one mineralogical group because of this high content of calcite. All these minerals can be present in a non-fired sample, hence this fact, together with the presence of non-fired organic matter described before, leads to an absence of firing during the manufacturing of this group of non-ceramic material.
Typological groups (de Capitani, 2002)

<table><thead><tr><th rowspan="2"></th><th colspan="10">Inclusion-poor silicate-rich matrix</th><th colspan="2">Inclusion-rich silicate-rich matrix</th><th colspan="2">Inclusion-rich carbonate-rich matrix</th></tr><tr><th>AI</th><th>AII</th><th>AIII</th><th>AIV</th><th>AV</th><th>AVI</th><th>BI</th><th>BII</th><th>CI</th><th>CII</th><th>CIII</th><th>Sum</th><th>Sum</th></tr></thead><tbody><tr><td>Pots Pfyn / Horgen</td><td>39</td><td>4</td><td></td><td>6</td><td>6</td><td></td><td>1</td><td></td><td>4</td><td></td><td></td><td>60</td><td>37%</td></tr><tr><td>SF Pfyn</td><td>2</td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>3</td><td>2%</td></tr><tr><td>SF Bayern</td><td>6</td><td></td><td></td><td></td><td>6</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td>13</td><td>8%</td></tr><tr><td>SF Boleráz</td><td>4</td><td></td><td></td><td>2</td><td>17</td><td>3</td><td></td><td></td><td>3</td><td></td><td></td><td>29</td><td>18%</td></tr><tr><td>USF</td><td>25</td><td></td><td></td><td>3</td><td>17</td><td>1</td><td>1</td><td></td><td></td><td>1</td><td></td><td>48</td><td>29%</td></tr><tr><td>Spindle whorls</td><td>7</td><td></td><td></td><td></td><td>3</td><td></td><td></td><td></td><td></td><td></td><td></td><td>10</td><td>6%</td></tr><tr><td>Cob fragments and Loom weight</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>12</td><td>----</td><td>----</td></tr><tr><td>Sum</td><td>83</td><td>4</td><td>1</td><td>11</td><td>49</td><td>4</td><td>2</td><td>3</td><td>5</td><td>1</td><td>----</td><td>163</td><td>100%</td></tr><tr><td>Sum</td><td>51%</td><td>2%</td><td>1%</td><td>7%</td><td>30%</td><td>2%</td><td>1%</td><td>2%</td><td>3%</td><td>1%</td><td>----</td><td>100%</td><td></td></tr></tbody></table>

Petrographical groups (thin section sketches)

SF: Special Forms, USF: Undetermined Special Forms; AI: mostly tempered with granite, AII: mostly tempered with rhyolite, AIII: mostly tempered with chert, AIV: mostly tempered with gabbro, AV: mostly tempered with grog, AVI: mostly tempered with bone; BI: mostly tempered with granite, BII: mostly tempered with grog; CI: mostly tempered with granite, CII: mostly tempered with organic material (loom weight), without temper (cob fragments).

<caption>Table 5.1: *Relations between typological and petrographical groups for every studied sherd.*</caption>
<figure><img src="image_27.png" /></figure>

**Figure 5.1 (part 1):** Pictures of thin sections. A: Petrographical group CIII: Inclusion-rich and carbonate-rich matrix, not tempered; (left): JB124, cob fragment, PL; (right): JB121, loom weight, tempered with organic material still present, PL. B: Petrographical group AI: Inclusion-poor and silicate-rich matrix mainly tempered with granite, JB003, CP (Crossed Polars). C: Petrographical group AII: Inclusion-poor and silicate-rich matrix mainly tempered with rhyolite, JB085C, CP. D: Petrographical group AIII: Inclusion-poor and silicate-rich matrix mainly tempered with chert, JB007, CP. E: Petrographical group AIV: Inclusion-poor and silicate-rich matrix mainly tempered with gabbro, JB049, CP. F: Petrographical group AV: Inclusion-poor and silicate-rich matrix mainly tempered with grog, JB004, PL (Plain Light).
<figure><img src="image_28.png" /></figure>

**Figure 5.1 (part 2):** Pictures of thin sections. G: Petrographical group AV: Inclusion-poor and silicate-rich matrix mainly tempered with grog, JB037: contains shell fragments (curved), PL.H: Petrographical group AVI: Inclusion-poor and silicate-rich matrix mainly tempered with bone, JB069, PL. I: Petrographical group BI: Inclusion-rich and silicate-rich matrix mainly tempered with granite, JB064, PL. J: Petrographical group BII: Inclusion-rich and silicate-rich matrix mainly tempered with grog, JB175, PL. K: Petrographical groups CI and CII: Inclusion-rich and carbonate-rich matrix mainly tempered with granite (CI) or grog (CII); here, CII is shown, JB073, PL. L: Inclusion-poor silicate-rich matrix of a clay from the surroundings of Arbon (JB301, CP).
<figure><img src="image_29.png" /><figcaption>**Figure 5.2:** The major chemical groups of Arbon Bleiche 3 (AB3): ceramics, bone tempered ceramics, cob fragments and loom weight, local clays.</figcaption></figure>

**5.5 CHEMICAL DESCRIPTION**

On Fig. 5.2, the major groups of Arbon Bleiche 3 (ceramics without bone temper, cob fragments and loom weight, ceramics tempered with bone, local clays) are presented in a CaO vs. SiO₂ (wt.%) concentration graph. This figure shows a good separation between the cob fragments and the loom weight on the one hand and the ceramics from Arbon Bleiche 3 on the other hand. Only one cob sample, JB127, consisted of a less carbonate-rich clay and plots near the ceramics. For all cob fragments, the SiO₂-content is in the range of the ceramics.

Appendix 9A shows the chemical variations of the cob fragments and the loom weight. Compared to the ceramics from Arbon Bleiche 3 (Appendix 9B), almost all the chemical elements have lower minimum and lower maximum values (SiO₂, TiO₂, Al₂O₃, Fe₂O₃, FeO, K₂O, Ba, Cu, Ni, Pb, Rb, V and Zn). Only CaO, Sr and Žr have higher minimum and maximum values. The rest of the elements are in the range of the ceramics. It implies that the clays used to make the loom weight and the house walls contained more calcium than those used to manufacture the ceramics.
# 6 - ARCHAOMETRICAL RESULTS CONCERNING THE CERAMIC MATERIAL: THE 163 SAMPLES OF POTTERIES AND SPINDLE WHORLS FROM ARBON BLEICHE 3

## 6.1 TYPOLOGICAL CLASSIFICATION OF THE POTTERY AND ITS RELATION WITH THE NEOLITHIC CULTURES FROM THE LAKE CONSTANCE TO THE WESTERN CARPATHIAN BASIN

The typological study of the pottery found in Arbon Bleiche 3 was made by Dr. A. de Capitani, archaeologist, in her PhD work (DE CAPITANI, 2002).

She defined two material groups, A and B by observing the sections of the sherds with a magnifying glass as follows: the sections showing only white grains as temper (i.e. rocks as temper) were distributed into group A, whereas the samples showing beige to brown grains (i.e. grog temper) were put into group B (DE CAPITANI, 2002, 143 and oral communication). Because all the ceramics were observed with a petrographic microscope in the present study, the previous distinction made by de Capitani was not used further on.

Then, de Capitani subdivided A and B into five different typological groups that will be described and used in this study (Table 6.1). Examples of ceramics from each typological group are shown in Fig. 6.1.

The first typological group described is the Pfyn / Horgen pots (subsection 6.1.1); the special forms (SF) are distributed into four groups (subsections 6.1.2 to 6.1.5). "In this group (special forms) you can find all kinds of vessels, which mostly cannot be derived from the Pfyn tradition. Comparisons cannot be made for all the special shapes, but some examples have parallels in the early period of the Baden culture (stage Boleráz), which mainly is prevalent in the Western Carpathian Basin, and within the Bavarian Altheim culture. " (DE CAPITANI, 2002, 374). The Bavarian Altheim culture (3800-3600 BC), followed by the Cham culture (3000-2800 BC) are also used to describe some parallels. However, these cultures are not strictly contemporaneous to Arbon Bleiche 3; their duration and repartition area are shown on Fig. 6.2.

<table><caption>**Table 6.1:** Relation between DE CAPITANI (2002) typological groups (n= reconstructed pottery) and BONZON (2004, 2005) petrographic groups (n= analysed reconstructed pottery).</caption><thead><tr><th rowspan="2"></th><th rowspan="2">Typological groups<br>(De Capitani, 2002)</th><th colspan="2">Materialgruppe</th><th rowspan="2">Bonzon<br>(n=)</th><th rowspan="2">Typological groups<br>(Bonzon, 2004, 2005)</th></tr><tr><th>A (n=)</th><th>B (n=)</th></tr></thead><tbody><tr><td rowspan="2">Töpfe</td><td>Pfyn / Horgen</td><td>178</td><td>33</td><td>60</td><td>Pfyn / Horgen pots</td></tr><tr><td>Pfyn</td><td>9</td><td>0</td><td>3</td><td>SF Pfyn</td></tr><tr><td rowspan="3">Sonstige<br>Formen</td><td>Bayern</td><td>4</td><td>10</td><td>13</td><td>SF Bayern</td></tr><tr><td>Frühen Badener Kultur (Stufe Boleráz)</td><td>3</td><td>33</td><td>29</td><td>SF Boleráz</td></tr><tr><td>Ohne Parallelen</td><td>46</td><td>38</td><td>48</td><td>USF</td></tr><tr><td colspan="2">Sum</td><td>240</td><td>114</td><td>153</td><td></td></tr></tbody></table>
<figure><img src="image_30.png" /><figcaption>**Figure 6.1:** Typical ceramics of every typological group: A: Pfyn / Horgen pot, B: special form Pfyn C: special form Bayern D: special form Boleráz E: undetermined special form. H: height, SF: special form, USF: undetermined special form, Inv. No.: Inventory Number, refers to Appendix 1 and DE CAPITANI (2002), JB...: refers to the sample number (drawings Archaeological service, Thurgau, M. Lier and E. Schön; from DE CAPITANI, 2002).</figcaption></figure>
<figure><img src="image_31.png" /><figcaption>**Figure 6.2:** Repartition and duration of the archaeological cultures discussed in this work. The arrows represent the possible travel of people in the Neolithic. M: Mödling-Jennyberg (Austria); Z: Žlkovce (Slovakia); N: Náměšť na Hané (Czech Republic)</figcaption></figure>

### 6.1.1 Pfyn / Horgen pots related to the Pfyn and Horgen cultures

The Pfyn / Horgen pots are the most abundant in the excavation: 70% of the ceramics studied by DE CAPITANI (2002, 161) are of that type. The pots (Fig. 6.1A) are grey to beige, “thick-walled, roughly slenderised and they have mostly a weak S-shape profile. The vessels are almost always unadorned: only now and then the neck is decorated with an encircling finger tapping, or fingernail incision band. There are some examples with a circular row of holes. Almost all the pots have knobs. On vessels with S-shaped profiles they are situated in the neck or just underneath. For the bottom shapes, flat standing and throated standing are almost equally represented” (DE CAPITANI, 2002, 374).

In the region around Arbon, the Pfyn culture (~3900-3600 BC) is followed by the Horgen culture (~3200-2800 BC) (STÖCKLI ET AL., 1995), as shown on Fig. 6.2. The village of Arbon Bleiche 3 was occupied during the transitional period between these two cultures. These vessels show at the same time characteristics of the Late Pfyn culture (around 3600 BC) – i.e. S-shaped profile, flat bottom, elongated lower body, barbotine covering, fingerprints, knobs – as well as those of the Eastern Horgen culture (around 3100 BC)

– i.e. conical to cylindrical profile, circular row of holes in the neck –. The pots from Arbon Bleiche 3 prove that the eastern Swiss Horgen culture has to be understood as resulting from a continuing development from the Pfyn culture.

### 6.1.2 Special forms Pfyn related to the Pfyn Culture

Only very few ceramics (9 samples) studied by the archaeologist (DE CAPITANI 2002, 155) are defined as special forms Pfyn. The pieces are of different shapes: 1 bottle, 3 miniature pots, 1 dish, 1 pot and 1 jar; the bottle is decorated with an encircling finger tapping and the outer surfaces of the pot and jar are both smoothed (Fig. 6.1B).

Special forms Pfyn are linked to the Pfyn tradition without any characteristics of the Horgen culture. Parallels with other Pfyn forms can be found in Steckborn Schanz (TG, CH) and the Thayngen Weier III (SH, CH).

### 6.1.3 Special forms Bayern related to the Altheim and Cham cultures from Bavaria

Another small group of ceramics (13 samples) studied by the archaeologist are defined as special forms Bayern (DE CAPITANI 2002, 156, 159).

This group includes small, large or double-conical dishes with knobs with finger impressions and cups with handles. The outer surface can be smoothed and an encircling finger tapping or fingernail incisions are sometime present. The sherds are also grey on both surfaces with thick walls (Fig. 6.1C).

Details of these ceramics are correlated with those of the Bavarian Altheim (3800–3600 BC) and Cham (3000–2800 BC) cultures (Fig. 6.2). These cultures are not contemporaneous to Arbon Bleiche 3, but the intermediate time between these two cultures is archaeologically very poorly described. Special forms Bayern from Arbon Bleiche 3 have parallels in Ergolding Fischergasse (D), Altheim (D), Alkofen (D), Galgenberg (D) und Koislhof (D) for the Altheim culture and Dobl (D) for the Cham culture (DE CAPITANI, 2002).
### 6.1.4 Special forms Boleráz related to the Boleráz stage of the Baden culture

Another group of the ceramics is special forms Boleráz (36 samples, DE CAPITANI 2002, 156, 158). They are cups or other bigger forms such as jars or amphorae with handles or handles with a hole to pass a string, and conical dishes. The ornaments are incised streaks that can form a fluted surface or that are arranged like fish-bone; very little buttons are also described with encircling fingernail incisions, or with a clay ring (Fig. 6.1D). These forms are thin (walls ≤ 8 mm), mostly black, polished and adorned.

Two particular samples (JB140 and JB149, DE CAPITANI 2002, Fig. 353, chapter 6.7) show the Boleráz' style, but are grey with thick walls. They are maybe local imitations of Boleráz pottery (DE CAPITANI, oral communication).

These ceramics are related to the early period of the Baden culture (Stage Boleráz, around 3500 BC), which is present in the western Carpathian Basin (Fig. 6.2). Special forms Boleráz have parallels with forms from Donnerskirchen (A), Mödling Jennyberg (A), Zlkovce (SK), Stúrovo (SK), Bratislava (SK), Nitrianshy Hrádok (SK), Blatné (SK), Jevisovice C1 (CZ), Brno-Lisen (CZ) and Staré Zámky (CZ).

### 6.1.5 Undetermined special forms

The remaining of the special forms (84 samples, almost 25% of the corpus studied by DE CAPITANI 2002 156, 160) contains all kinds of forms, with no resemblance to known ceramics: they are classified as undetermined special forms (USF). They are of diverse colours (mostly grey and black), their walls are thin or thick, their surfaces are smooth or rough, or covered with barbotine, they are decorated or not, and come with or without handles (Fig. 6.1E).

<figure><img src="image_32.png" /><figcaption>**Figure 6.3:** Sewed section of sherd JB083 (Pfyn / Horgen pot studied in Bonzon, 2005): four coils were detected after sewing, separated by holding surfaces AB, BC & CD.</figcaption></figure>

## 6.2 MACROSCOPIC DESCRIPTION

### 6.2.1 Pfyn / Horgen pots

The Pfyn / Horgen pots (Fig. 6.1A) are coarse ceramics, grey to beige coloured on both outer and inner surfaces and on the sections. The latter contains sometimes black areas in the core or on the inner or outer margin. Barbotine covered some pots. The walls are around 1 cm thick (± 2 mm) and coil-built (see Fig. 6.3, Appendix 12 and BONZON 2005). The temper is composed of medium to large angular white grains (2-10 mm Ø, rock fragments) and/or of beige to brown grains (grog). The outer surface is often black due to the use of these ceramics on open fire. A black crust, remain of organic cooked matter, sometimes covers the inner surface from the bottom up to the middle of the pots.

The thick-walled ceramics of Arbon Bleiche 3 are characterised by a quasi systematic presence of dark-brown carbonised organic residues adhering to the internal surface. They are to be found in the first third of the ceramics from the basis. The function of these pots was essentially culinary (REGERT ET AL., 1999) and the study of such residues (on Horgen pots of Chalain) proved the use of animal fats (ruminants principally), of beeswax and milk products. The organic crusts of Arbon Bleiche 3 are made of the same material (except beeswax) (SPANGENBERG, oral communication).

### 6.2.2 Special forms Pfyn and special forms Bayern

Special forms Pfyn and special forms Bayern (Fig. 6.1: B, C) have a similar macroscopic aspect to the pots. Rare pieces have thinner walls (8-10 mm) and medium temper. Coils are normally thinner, when visible (lost during fabrication?; MARTINEAU 2000, 2002).

### 6.2.3 Special forms Boleráz

Special forms Boleráz (Fig. 6.1D) have thinner walls (5-8 mm) and are normally black, or grey with a black core. The temper grains are mostly beige to brown (grog), small (≤ 4 mm Ø), and small white grains or fragments (rocks) can be present. Three samples of this group contain black long thin fragments (bone). No coils are detected in this group; these ceramics were probably built with a different tech-
nique (slab building technique?), which could explain their delicacy.

Without the use of advanced analytical tools, it is difficult to ascertain the presences of coloured bone material in a ceramic matrix. It is for example not possible to distinguish with certainty bone fragments from grog temper only by visual inspection, even when aided by a magnifying glass. Dark colours are characteristic for bone material and the shape helps to distinguish them from organic remains (also black but with proper shapes). Nevertheless, attention has to be paid to their similarity with black rocks.

### 6.2.4 Undetermined special forms

Undetermined special forms (USF; Fig. 6.1E) do not form a homogeneous group. All the features described above were observed, even fragments of bone in one sample (JB012).

### 6.2.5 Spindle whorls

The spindle whorls have a diameter between 45 and 57 mm, and a thickness between 8 and 15 mm. All are flat, except JB112 and JB116, which are conical and double conical respectively. Seven spindle whorls are thick (11-15 mm), beige to grey and resemble in its macroscopic appearance sherds of Pfyn / Horgen pots. Three are thin (6-9 mm), black and similar to the sherds of the special forms Boleráz.

## 6.3 PETROGRAPHICAL STUDY

### 6.3.1 Introduction

The petrographical description of each sample is presented in Appendix 3.

The petrographical study, based on the nature and relative quantity of the matrix and temper(s), permitted to separate the samples into 11 petrographical groups shown on Table 5.1. The samples are split into the different petrographical groups based on the nature of their matrix (inclusion-poor or inclusion-rich, silicate-rich or carbonate-rich), and then, based on the nature and proportion of the temper (mainly rock,

nature of the rock; mainly grog; mainly bone). Fig. 5.1 illustrates every single group with a picture of a portion of one representative thin section.

Mineralogical changes due to firing are often observed in the thin sections of Arbon Bleiche 3 and were previously described by COURTOIS (1976) and MAGGETTI ET AL. (1984): Quartz are often broken into several fragments. Feldspars show twins, microperthites between orthoclase and albite and micropegmatites in association with quartz. Amphiboles show rubefaction, the initial homogeneously green specimens develop red borders at 700°C, a process which is terminated at 800°C when the amphiboles become homogeneously red. Biotites are altered: they either only keep their pleochroism in parts or are made opaque; they rarely show half-opened flakes due to vermiculitisation. In Arbon Bleiche 3 as in MAGGETTI AND SCHWAB (1982), the sherds reflect the alpine source of their temper and natural inclusions by their content of biotite from granites and strongly saussuritised plagioclases, typical for the alpine metamorphic rocks.

### 6.3.2 Inclusion-poor and silicate-rich matrix: petrographical groups AI-AVI

#### 6.3.2.1 Petrographical group AI: granite temper

Petrographical group AI (Fig. 5.1B) is tempered either with granite only, or is dominated by granite, with minor proportions of gabbro, rhyolite, chert or grog. The temper is normally coarse (0.5 to 10 mm Ø), angular to sub-angular, and its proportion varies between 2 and 25 vol.%. Accessory minerals are present in various proportions, such as biotite (often altered), epidote and zircon.

About 80% samples present little iron oxide nodules in the matrix (< 0.5 mm Ø). ARF are also visible, but small (< 3 mm Ø).

83 of the 163 ceramics (51%) belong to this group. It is the main petrographical group of Arbon Bleiche 3 (Table 5.1). In this principal group, all the different typological groups are found: Pfyn / Horgen pots (47%), undetermined special forms (30%), spindle whorls (9%), special forms Bayern (7%), special forms Boleráz (5%) and special forms Pfyn (2%).
### 6.3.2.2 Petrographical group AII: rhyolite temper

Petrographical group AII (Fig. 5.1C) is mostly tempered with rhyolite, plus granite, gabbro or grog in minor proportions. The description of the temper is similar to the one of group AI, except its amount (10-20 vol.%). The same accessory minerals as described in group AI are present.

The samples present little iron oxide nodules in the matrix (< 0.5 mm Ø). ARF are also visible, but small (< 3 mm Ø).

Four of the 163 ceramics (2%) belong to this group (Table 5.1), which only contains the typological group of the Pfyn / Horgen pots.

### 6.3.2.3 Petrographical group AIII: chert temper

Petrographical group AIII (Fig. 5.1D) is mostly tempered with chert, plus granite, gabbro and grog in minor proportions. The description of the temper is similar to the one of group AI. Iron oxide nodules and ARF are also present. Only one sample of special form Pfyn belongs to this group (Table 5.1).

### 6.3.2.4 Petrographical group AIV: gabbro temper

Petrographical group AIV (Fig. 5.1E) is mostly tempered with gabbro, plus granite, rhyolite, chert or grog in minor proportions. The description of the temper is similar to the one of group AI, except its amount, varying between 7 and 25 vol.%. The same accessory minerals as described in group AI are present. About 50% of the samples present little iron oxide nodules in the matrix (< 0.5 mm Ø). ARF are also visible, but small (< 3 mm Ø).

Eleven ceramics (7% of the samples) belong to this group (Table 5.1). AIV is constituted of the following typological groups: 55% Pfyn / Horgen pots, 27% undetermined special forms and 18% special forms Boleráz.

### 6.3.2.5 Petrographical group AV: grog temper

Petrographical group AV (Fig. 5.1F) is either tempered with grog only, or mainly with grog together with granite, gabbro, rhyolite or chert in minor proportions. The temper, usually rounded, is thinner than the rock fragments described before (0.5-8 mm Ø), and its

proportion varies between 2 and 15 vol.%, with one exception of 25 vol.%. Grog looks like the silicate-rich clay and if often tempered with granite similar to that of AI. Only biotite is often present as accessory minerals; epidotes and zircons are rare. ARF (particles size: 0.5-3 mm Ø) are rarely present as inclusions, and no iron oxide nodule was observed. In one sample (JB037), many shell fragments are present (gastropods and lamellibranches, Fig. 5.1G). MAGGETTI AND NUNGÄSSER (1981) described 2-5 % of the vessels from the Cortaillod culture from Twann containing shell fragments as temper. These fragments were described as brachiopods shells (Rhynchonels); gastropods shells were also present, but rare. However, this kind of temper is not frequently described in the literature, as far as we know.

This petrographical group contains 49 samples (30% of the samples) and is the second most important group of Arbon Bleiche 3 (Table 5.1). AV is constituted of the following typological groups: 35% special forms Boleráz, 35% undetermined special forms, 12% Pfyn / Horgen pots, 12% special forms Bayern and 6% spindle whorls.

### 6.3.2.6 Petrographical group AVI: bone temper

Petrographical group AVI (Fig. 5.1H) is tempered either principally or exclusively of bone fragments (1-2 mm long). They are yellow, beige, dark brown, black or grey in plain light (Fig. 6.4A); the colours are randomly distributed in the sections, except in JB012 composed only of black fragments. For example, JB069 has a black core due to the firing process, but the coloration of the bone fragments do not correspond to the colour of the surrounding matrix. The fragments also can be two-coloured yellow and dark-brown to black (Fig. 6.4B); they are neither distributed in relation to the surface of the pottery. The firing of the ceramics is, therefore, not the origin of the coloration. In figure 6.4B, the two fragments next to the outer surface are yellow towards the outside and black towards the inside of the thin section, whereas in the upper part of the picture, one grain has a reversed colour scheme, outside black, inside yellow.

In sample JB069, 20 vol.% bone temper is present (Fig. 5.1H). JB012 contains 10 vol.% of black bone fragments and 10 vol.% of grog (1-3 mm Ø). JB020 and JB147 are tempered respectively with 20 and 10 vol.% bone, 10 and 7 vol.% grog and 5 and 2 vol.% granite.
The accessory minerals are the same as those described in the petrographical group AV and no iron nodule is present.

AVI petrographical group is composed of four ceramics (2% of the samples): three special forms Boleráz and one undetermined special form (Table 5.1); it is the particular petrographical group of Arbon Bleiche 3.

### 6.3.3 Inclusion-rich and silicate-rich matrix: petrographical groups BI and BII

#### 6.3.3.1 Petrographical group BI: granite temper

Petrographical group BI (Fig. 5.1I) is the matching piece to group AI: its temper is mostly granite, together with chert or grog in minor proportions. The rock temper is coarse and its proportion is of 7 vol.% in one case and 15 vol.% in the other one. The description of the temper, the accessory minerals, the ARF and the iron oxide nodules are similar to the one of group AI.

Two ceramics belong to this group (Table 5.1). One sample is a Pfyn / Horgen pot, and the other one an undetermined special form.

#### 6.3.3.2 Petrographical group BII: grog temper

Petrographical group BII (Fig. 5.1J) is matching to group AV. One sherd is only tempered with grog and

two are mostly tempered with grog, together with granite or gabbro in minor proportions. The temper, the accessory minerals and the ARF are similar to the one of group AV. The grog proportion is 5 vol.%. Three ceramics (~2% of the samples) are part of this group and typologically belong to special forms Boleráz (Table 5.1).

### 6.3.4 Inclusion-rich and carbonate-rich matrix: petrographical groups CI and CII

#### 6.3.4.1 Petrographical group CI: granite temper

Petrographical group CI (Fig. 5.1K) is the matching piece to groups AI and BI: 3 samples are only tempered with granite, and 2 are mostly tempered with granite, together with gabbro or grog in minor proportions. The temper, the accessory minerals, the ARF and the iron oxide nodules are the same as those described in group AI. The proportion of temper varies from 10 to 20 vol.%.

Five ceramics (3% of the samples) belong to this group. 4 samples are Pfyn / Horgen pots, and one is an undetermined special form (Table 5.1).

#### 6.3.4.2 Petrographical group CII: grog temper

Petrographical group CII (Fig. 5.1K) is matching to groups AV and BII. Only one ceramic belongs to this group and is tempered with 10 vol.% grog and 2

<figure><img src="image_33.png" /><figcaption>**Figure 6.4:** A: Yellowish and black bone fragments as temper in thin section JB020. Black fragments are underlined with red colour.
B: Two-coloured bone fragments visible in thin section JB069.</figcaption></figure>
vol.% granite (Table 5.1). The temper, the accessory minerals and the ARF are as described in group AV.

The sample of this petrographical group is typologically bound to special forms Bayern.

## 6.4 SPECIFIC STUDIES ON BONE TEMPERED CERAMICS

### 6.4.1 Introduction

Four samples of petrographical group AVI contain more than 10 vol.% bone fragments. Such fragments were never observed for the Neolithic period in Switzerland. MORZADEC (1992) described bone temper in some rare Mid-Neolithic ceramics from the Paris Basin, the North of France, Bretagne, Alsace and from La Hoguette site. This type of temper disappears in France during final Neolithic (MORZADEC, 1993). CONSTANTIN AND COURTOIS (1976) dated the ceramics containing bone temper in France roughly between 4000 and 3500 BC. The decoration of the bone temper ceramics from the Paris Basin are typologically alike the Limbourg ceramics, observed in the Neolithic of Holland. Bone fragments were also observed in the latter group (CONSTANTIN AND COURTOIS, 1985).

### 6.4.2 Firing

The firing of the ceramics is not the origin of the coloration of the fragments of bone. Their colours are rather linked to a primary heating of the bone. A heat treatment of the bone fragments is necessary to break them into pieces, because raw bones are too elastic to be crushed into very little fragments (CONSTANTIN & COURTOIS, 1985). Reddish brown, very dark grey-brown, neutral dark grey, or reddish-yellow colours are typical of heating Stage II (temperature 285-<525°C) in bone tissues defined by SHIPMAN ET AL. (1984). Most of these colours are also observed in our samples. The annealing temperature of the bone fragments has, therefore, been probably less than 525°C. Following SHIPMAN ET AL. (1984), the absolute smooth surface of the bone fragments visible in SEM pictures (Fig. 6.5) is typical in heating Stage III in bone tissues (temperature 285-<440°C): "the pores and asperities typical of Stage II disappear, the bone surface becomes glassy and smoother than it was in Stage I. Areas of bone may take a vitrified appearance." (314, table 5). Therefore, the bone fragments must not have reached more than 440°C.

The broad peaks between 32 and 35° 2q in the XRD patterns (Appendix 5) are typical for nanocrystalline bone apatite. X-ray patterns of bone that has not experienced temperatures above 400°-450°C is characterized by a single broad peak centred at 33°C (SHIPMAN ET AL., 1984), such as seen in the pattern of JB147. The firing temperature of this ceramic could have been higher than 400°C, provided the temperature treatment did not last to long (MAGGETTI, oral communication). The ceramics were fired mostly under reducing conditions, as shown by their black heart. JB020 has been fired at lower temperature than the other samples, because chlorite is still present (< 550-600°C, NUNGÄSSER ET AL., 1985). The firing temperatures are higher for JB147, JB069 and JB012, because the peaks of illite are less and less visible. JB012 has probably been fired at temperatures about 800°C, which would explain the absence of illite (NUNGÄSSER ET AL., 1985; LETSCH & NOLL, 1983). JB147 & JB069 were probably fired between 600 and 800°C. The presence of pyrite can be secondary and resulting from the deposition of the sherds in a reducing environment (NUNGÄSSER ET AL., 1985).

### 6.4.3 Scanning electron microscope (SEM)

The coloured fragments have always a smooth appearance in SEM pictures and are easy differentiable from the surrounding ceramic matrix (Fig. 6.5A). At high magnification, Havers canals (pores originally containing blood vessels, lymphatic vessels and nerves) are observed (Fig. 6.5B) and prove the bone nature of the fragments.

The kind of bone used and its provenance is very difficult to determine. Only some fish bone are excluded, because they present special characters (i.e. special shaped little elements or fragments of some other looking like circles) visible under a microscope (communication HÜSTER-PLOGMANN). The microstructures, such as the almost total absence of holes and spongy parts, are typical for long bones (tibia, fibula etc.; MORZADEC, 1993). The heat treatment that the bone fragments suffered excludes a DNA analyses that could tell the origin of bone (WATSON ET AL., 1994). The use of human bone cannot be excluded, because the histology of bone cannot give any negative or positive evidence on that question.
<figure><img src="image_34.png" /><figcaption>Figure 6.5: A: Bone temper (smooth surface) observed with SEM, with position of picture B. Note that the surrounding fired clay has an irregular surface. On picture B, Havers canals are circled.</figcaption></figure>

<table><caption>**Table 6.2:** Chemical data of the four bone tempered ceramics in regard to mean and standard deviation (s) of all the other ceramics from Arbon Bleiche 3 (n= 158, see Appendix 9B). √, + and - respectively refer to “equal to”, “more” or “less” than the range of “mean plus or minus s” for 158 ceramics from Arbon Bleiche 3.</caption><thead><tr><th colspan="2">Oxides</th><th colspan="4">Bone tempered ceramics</th><th colspan="2">Other ceramics</th></tr><tr><th>Elements</th><th>Unit</th><th>JB012</th><th>JB020</th><th>JB069</th><th>JB147</th><th>mean</th><th>s</th></tr></thead><tbody><tr><td>SiO2</td><td>wt.%</td><td>56.18 -</td><td>53.11 -</td><td>56.92 -</td><td>59.10 -</td><td>67.84</td><td>2.18</td></tr><tr><td>TiO2</td><td>wt.%</td><td>1.60 +</td><td>0.64 √</td><td>0.62 -</td><td>0.75 √</td><td>0.73</td><td>0.09</td></tr><tr><td>Al2O3</td><td>wt.%</td><td>28.48 +</td><td>16.31 -</td><td>15.31 -</td><td>18.01 √</td><td>17.87</td><td>1.39</td></tr><tr><td>Fe2O3*</td><td>wt.%</td><td>6.30 +</td><td>4.38 √</td><td>3.42 -</td><td>4.31 √</td><td>4.61</td><td>0.70</td></tr><tr><td>MnO</td><td>wt.%</td><td>0.03 √</td><td>0.04 √</td><td>0.06 √</td><td>0.04 √</td><td>0.05</td><td>0.02</td></tr><tr><td>MgO</td><td>wt.%</td><td>0.86 -</td><td>2.07 √</td><td>1.56 √</td><td>2.25 +</td><td>1.76</td><td>0.42</td></tr><tr><td>CaO</td><td>wt.%</td><td>2.67 √</td><td>12.30 +</td><td>14.00 +</td><td>7.60 +</td><td>3.10</td><td>1.74</td></tr><tr><td>Na2O</td><td>wt.%</td><td>0.31 -</td><td>0.54 √</td><td>0.30 -</td><td>0.72 √</td><td>0.91</td><td>0.47</td></tr><tr><td>K2O</td><td>wt.%</td><td>1.83 -</td><td>2.32 -</td><td>2.09 -</td><td>2.84 √</td><td>2.88</td><td>0.42</td></tr><tr><td>P2O5</td><td>wt.%</td><td>1.12 +</td><td>8.00 +</td><td>5.53 +</td><td>4.29 +</td><td>0.23</td><td>0.09</td></tr><tr><td>Ba</td><td>ppm</td><td>799 +</td><td>663 √</td><td>651 √</td><td>848 +</td><td>663</td><td>133</td></tr><tr><td>Cr</td><td>ppm</td><td>214 +</td><td>104 √</td><td>104 √</td><td>117 √</td><td>113</td><td>18</td></tr><tr><td>Cu</td><td>ppm</td><td>42 √</td><td>36 √</td><td>35 √</td><td>52 +</td><td>39</td><td>8</td></tr><tr><td>Nb</td><td>ppm</td><td>34 +</td><td>13 √</td><td>15 √</td><td>19 +</td><td>16</td><td>3</td></tr><tr><td>Ni</td><td>ppm</td><td>124 +</td><td>68 √</td><td>57 √</td><td>61 √</td><td>63</td><td>13</td></tr><tr><td>Pb</td><td>ppm</td><td>66 +</td><td>29 √</td><td>24 √</td><td>14 -</td><td>27</td><td>5</td></tr><tr><td>Rb</td><td>ppm</td><td>103 -</td><td>135 -</td><td>119 -</td><td>143 √</td><td>159</td><td>23</td></tr><tr><td>Sr</td><td>ppm</td><td>212 √</td><td>305 +</td><td>282 +</td><td>226 √</td><td>191</td><td>55</td></tr><tr><td>V</td><td>ppm</td><td>194 +</td><td>114 √</td><td>112 √</td><td>128 √</td><td>122</td><td>20</td></tr><tr><td>Y</td><td>ppm</td><td>444 +</td><td>30 +</td><td>26 √</td><td>31 +</td><td>25</td><td>4</td></tr><tr><td>Zn</td><td>ppm</td><td>184 +</td><td>137 +</td><td>109 √</td><td>123 √</td><td>109</td><td>19</td></tr><tr><td>Zr</td><td>ppm</td><td>388 +</td><td>123 -</td><td>125 √</td><td>139 √</td><td>152</td><td>27</td></tr><tr><td>SUM</td><td>wt.%</td><td>99.66</td><td>99.89</td><td>99.98</td><td>100.10</td><td></td><td></td></tr><tr><td>FeO</td><td>wt.%</td><td>1.90</td><td>2.43</td><td>1.54</td><td>2.88</td><td></td><td></td></tr><tr><td>LiO</td><td>wt.%</td><td>15.48</td><td>10.84</td><td>9.24</td><td>12.92</td><td></td><td></td></tr></tbody></table>
### 6.4.4 Chemical study

Fig. 5.2 shows the clear separation between all the ceramics from Arbon Bleiche 3 on the one hand and the four samples containing bone temper on the other hand: CaO is present respectively between 1 wt.% and 9 wt.%, and between 2 wt.% and 14 wt.%; SiO₂ values vary between 65 wt.% and 75 wt.% and between 53 wt.% and 60 wt.% respectively. Moreover, this distinction is evident, chemically speaking. Table 6.2 and Appendix 9C show the chemistry of these samples and their descriptive statistics. Compared to all the other ceramics from Arbon Bleiche 3 (Table 6.2 and Appendix 9B), these exceptional potteries are quite different. JB012 has only four oxides and chemical elements that are situated in the mean range of all other ceramics from Arbon Bleiche 3; SiO₂, MgO, Na₂O, K₂O and Rb are below the mean range whereas TiO₂, Al₂O₃, Fe₂O₃tot, P₂O₅, Ba, Cr, Nb, Ni, Pb, V, Y, Zn and Zr values are above this range. As for JB020, JB069 and JB147, they share the same trend, deficient in SiO₂ and with high values of CaO and P₂O₅. This has to be put in relation with the presence of bone as temper, which is principally composed of Ca and P. Other chemical differences (excess of Sr, Y and Zn in JB020, of Sr in JB069 and of MgO, Ba, Cu, Nb and Y in JB147; lack of Al₂O₃, K₂O, Rb and Zr in JB020, of TiO₂, Al₂O₃, Fe₂O₃tot, Na₂O, K₂O, Rb in JB069 and of Pb in JB147) are to be noticed but cannot be explained yet. However, it shall be pointed out that even if JB012 is chemically very different from all the “normal” ceramics from Arbon Bleiche 3, the three other ceramics tempered with bone are not chemically similar with one another. These four are petrographical and chemical exceptions and will not be used in further statistical analyses.

### 6.4.5 Microprobe

The combined XRD, XRF and the microprobe remove the last doubts on the bone nature of the fragments. The main inorganic constituent of bone is apatite, a phase with composition Ca₅(PO₄)₃(X) (NESSE, 2000). Three end members with X = F, OH, and Cl are known. The crystal chemistry of bone apatite is still disputed. Despite being called hydroxylapatite or carbonated hydroxylapatite in the medical literature, recent IR, Raman and NMR spectroscopy revealed no sign of OH-groups in mouse bones and moderate quantities in enamel (PASTERIS ET AL, 2001). Bone apatite is characterized by its nanocrystalline texture and the presence of CO₃²⁻ groups, which replace PO₄³⁻

groups, anions on the X-site or both. HANDSCHIN AND STERN (1994) calculated weight percents of fluorapatite: 55.60 wt.% CaO, 42.22 wt.% P₂O₅ and 3.77 wt.% F, which gives a CaO/P₂O₅ ratio of 1.32 and a P₂O₅/F ratio of 11.14. The closest microprobe analyse of apatite gives a CaO/P₂O₅ ratio of 1.33 and a P₂O₅/F ratio of 11.20 (37.11 wt.% CaO, 27.94 wt.% P₂O₅ and 2.51 wt.% F). The mean on 98 microprobe analyses gives a ratio Ca/P of 2.03 (Fig. 6.6). The same ratio in HANDSCHIN & STERN (1994) is of 2.18. The variation between these two results is surely due to the presence of an apatite with OH partially replacing fluorine, Ca₅(PO₄)₃(OH,F). During burial, the fluorine is leached and hydration from the surrounding wet ground permits OH to replace partially the F component (RYCHNER-FARAGGI AND WOLF, 2001).

## 6.5 FIRING OF THE POTTERIES AND SPINDLE WHORLS FROM ARBON BLEICHE 3

### 6.5.1 Firing process

See also chapter 3.4.

Surface treatment after the firing was not observed in the ceramics from Arbon Bleiche 3: no sample has a black surface resulting from a pre- or post-firing treatment. Hence, we will only describe the three first parts (core, outer and inner margins, Fig. 3.8). They will permit to describe all the phenomena that happened during the firing process.

The archaeologists found no trace of bonfire or pit-firing in Arbon Bleiche 3, and were therefore not able

<figure><img src="image_35.png" /><figcaption>**Figure 6.6:** Microprobe measurements in bone temper, Ca/P ratio is equal to 2.03.</figcaption></figure>
to determine the type of firing, like in other Neolithic villages of Switzerland (DE CAPITANI, oral communication). Hence, the Neolithic people could have used either bonfire or pit firing methods. Even the coloration of the sherds does not permit to detect which firing method was used.

With the help of the thin sections, the ceramics from Arbon Bleiche 3 could be separated into five colour groups (Appendix 4):

- Colour group 1: the section of the sherds has a plain colour (grey, yellowish-beige or orange; no black)

- Colour group 2: the section is completely black

- Colour group 3: the inner margin is black and the outer margin coloured

- Colour group 4: the core of the section is black and both inner and outer margins are coloured

- Colour group 5: the outer margin is black and the inner margin coloured.

Colour group 1 corresponds to a simple bonfire (or pit fire) firing: the rise of temperature without available oxygen followed by a cooling with available oxygen; the potter lets the ceramics in the firing area until they are cold. (Phases I, II, III, IVa or IVb and V: MARTINEAU AND PÉTREQUIN, 2000).

Colour group 2 corresponds to a heating and a cooling without available oxygen: the best way to attain this is to use a pitfiring process and to cover the pit after the plateau to induce a confined atmosphere (Phases I, II and III, followed by a confined atmosphere; MARTINEAU AND PÉTREQUIN, 2000).

Colour group 4 corresponds to a heating without available oxygen followed by a cooling with available oxygen; the oxygen reacted with both margins during

the cooling. This can be attributed to a bonfire (or a pit firing) where the ceramics are not piled up (Phases I, II, III and IVa; MARTINEAU AND PÉTREQUIN, 2000). The difference between colour group 4 and 1 (plain colour) is related to the firing time: colour group 1 implies a long cooling, so that the oxygen has enough time to enter the section of the ceramic entirely. In contrast, colour group 4 experienced only a short and rapid cooling, so that the oxygen interacted only with the margins. It had no time to penetrate the core. The potter takes the ceramics out of the fire, to cool in fresh air or even in water.

Colour group 3 looks like group 4, but the ceramics were probably piled up, obstructing the oxygen entering the inner margins (Phases I, II, III and IVb; MARTINEAU AND PÉTREQUIN, 2000). Note that a thin coloured margin results from a rapid cooling (i.e. the potter takes the ceramics out of the fire when they are warm); whereas a large one implies a long cooling (i.e. the potter lets the ceramics in the firing area during the cooling).

Colour group 5 is a real problem. Following MARTINEAU AND PÉTREQUIN (2000) these sherds should not exist. A simple firing cannot explain their colouration. The only explanation that can be proposed is that the ceramics got burnt a second time by the fire which destroyed the village of Arbon Bleiche 3. Therefore, some coloured sherds, covered by falling wood debris could fire once again in a confined atmosphere. This can lead to a sherd with an outer black part and an inner coloured part. Sometimes, the outer part can correspond to the outer margin of a ceramic. This group had to be fired twice to explain the presence of an outer black margin. (Phases I, II, III, IVa or IVb and V,

<figure><img src="image_36.png" /><figcaption>**Figure 6.7:** Reduction index (calculation of the ratio FeO/FeOtot) for JB001-JB154: about 80% of the samples were fired in a reducing atmosphere (reduction index > 0.30) (n: number of samples, black-and-white rectangles show the sections of the sherds, outside on the right-hand side; in colour group 1, dots are the yellowish-beige samples and black diamonds are the grey ones).</figcaption></figure>
followed by a fire, which burnt down the entire village; MARTINEAU AND PÉTREQUIN, 2000).

To resume, colour group 2 was fired under confined conditions followed by a confined cooling atmosphere, whereas the other colour groups (1, 3, 4) were fired under confined conditions, followed by a cooling with available oxygen. A second firing in confined conditions, the burning down of the village, possibly modified colour group 5.

## 6.5.2 Firing atmosphere

The stability of the firing atmosphere is described using the FeO/FeOtot ratio (MAGGETTI AND SCHWAB, 1982). This reduction index shows the intensity of the iron reduction during the firing. When a firing is surveyed, the ratio is quite similar for two sherds of the same firing process. When the variation is very important (0.1 to 1 in KILKA AND GALETTI, 1994), it indicates a non-followed firing.

FeO was measured only for JB001 to JB154. The diagram of Fig. 6.7 shows the intensity of the reduction during the firing for these ceramics. Because those samples represent the majority of the studied samples and all the typological groups, the range of variation determined here is thought to be representative of all the ceramics from Arbon Bleiche 3.

The rare sherds that are homogeneously coloured are shown in Appendix 4, as colour group 1. They are yellowish-beige or grey. The yellowish-beige ones had time to completely re-oxidise during the cooling, contrary to the grey ones. These latter have to be put into relation to those of colour group 2 that are totally black. On figure 6.7, the yellowish-beige ones are symbolised by a dot and four among them are below 0.3 (ratio FeO/FeOtot; JB016, JB119, JB134, JB149). Moreover, all the reduced black samples (colour group 2) have a ratio higher than 0.3. We suggest 0.3 as the limit between the oxidising and the reducing atmosphere. However, the other yellowish-beige ones (JB019, JB022, JB032, JB037) situate between 0.3 and 0.4, hence in the reducing atmosphere area! Probably some parts of the sherds were still greyish (still reduced) but not visible to the naked eye.

Note that in the literature (MAGGETTI AND SCHWAB, 1982; KILKA AND GALETTI, 1994), the limit between the oxidising and the reducing atmospheres is frequently around 0.2. This difference may be put in relation

to the fact that in a Neolithic open firing, the atmosphere is not always stable and can vary rapidly. The large variation of the reduction index (0.1 to 0.9) proves a non-followed firing. In such a case, "jumps" during the firing and the cooling between oxidising and reducing atmospheres are probable.

For colour groups 3 to 5, FeO was measured on the whole sherd. Due to its banded aspect (black and various colourations) the reduction index changes from one part to another. Hence, the reduction index represents the average of these differently coloured areas. It shows, for the major part of the ceramics, a reducing atmosphere of firing (reduction index > 0.3).

Hence, almost 80% of the samples from Arbon Bleiche 3 were fired in a dominantly reducing atmosphere (> 0.3); only 30 on 154 samples (19%) cooled and were maybe partially fired in an oxidising atmosphere (colour group 1: JB016, JB019, JB022, JB032, JB037, JB119, JB134, JB149; colour group 3: JB004, JB007, JB010, JB026, JB038, JB061, JB076, JB089, JB090, JB092, JB094, JB097, JB135; colour group 4: JB024, JB031, JB033, JB073, JB095, JB107, JB144; colour group 5: JB034 and JB088).

## 6.5.3 Mineralogical transformations during firing

### 6.5.3.1 Nota Bene

The chemical study presented further will show that JB302 (carbonate-rich clay) and JB301 (silicate-rich clay) seem to fit quite well with the clays used to manufacture respectively the non-ceramic material and the ceramics from Arbon Bleiche 3. However, the experimental firings discussed underneath were made on JB304 (carbonate-rich clay) and JB306 (silicate-rich clay). Indeed, at that time, the chemical study was not achieved and these results not yet known.

### 6.5.3.2 Experimental oxidising firing of a carbonate-rich clay from the surroundings of Arbon

An experimental firing in a furnace was performed on an inclusion-rich and carbonate-rich clay collected in the surroundings of Arbon (Fig. 2.11, JB306). Figure 6.8 shows the mineral associations present in this clay between 20°C and 1000°C. The clay in its natural state (at 20°C) is composed of smectite, chlorite, illite, quartz, K-feldspar, plagioclase, calcite and dolomite.
At 1000°C, the mineralogical association of the transformed clay is composed of residues of illite, of quartz, K-feldspar, plagioclase, lime, hematite, gehlenite and diopside. The mineralogical transformations of this "JB306-experiment" as a function of temperature are put into relation with the results of the literature in Appendix 7A and discussed here.

In the "JB306-experiment", the disappearance of the different peaks of chlorite was not distinguishable (in opposition with BENGHEZAL, 1994A) and the mineral disappeared below 600°C, lower than what is proposed in the literature in which chlorite disappears between 650° and 700°C (TITE, 1995; BÉARAT, 1992 and JORNET ET AL., 1985). The smectite disappeared

below 500°C, in accordance with the results of BENGHEZAL (1994A). At 1000°C, the two major peaks of illite (002: 10Å and 110: 4.48Å) are still visible, implying its disappearance above this temperature. Quartz, plagioclase and K-feldspar are also always present. Dolomite disappears at the same temperature as calcite, i.e. near 750°C, around the temperature proposed in CULTRONE ET AL. (2001). Hematite is present from 700°C to over 1000°C, which does not exactly correspond to the literature. Gehlenite and diopside form around 800°C and are still present at 1000°C, in accordance with the results of BENGHEZAL (1994A) and CULTRONE ET AL. (2001).

<figure><img src="image_37.png" /><figcaption>**Figure 6.8:** Mineralogical changes between 20° and 1000°C (oxidising atmosphere) for two local clays from the surroundings of Arbon. JB306 (upper part) is a carbonate-rich clay; JB304 (lower part) is a silicate-rich clay. Note: smectite is probably a mixed layer illite/smectite as observed in Table 8.3.</figcaption></figure>
### 6.5.3.3 Experimental oxidising firing of a silicate-rich clay from the surroundings of Arbon

The same kind of firing was performed on an inclusion-poor and silicate-rich clay collected in the surroundings of Arbon (Fig. 2.11, JB304). The clay in its natural state (at 20°C) is composed of smectite, chlorite, illite, quartz, K-feldspars and plagioclases (Fig. 6.8). At 1000°C, the new mineralogical association is composed of quartz, K-feldspar, plagioclase, hematite and spinel. The mineralogical transformations of this “JB304-experiment” as a function of temperature are put into relation with the results of the literature in Appendix 7B and discussed below.

MAGGETTI (1979) quoted GRIM (1968) who measured at 550°C that chlorite had disappeared, which is in accordance to the observation of the “JB304-experiment”. The same temperature is observed for smectite, as proposed in PICOUET (1997), MAGGETTI (1993) and BENGHEZAL (1994A). All the peaks of illite reduced to 900°C and had disappeared around 950°C, which is not exactly what is proposed in the literature. Quartz always stays, whereas K-feldspar and plagioclase are much reduced at 1000°C.

The “JB304-experiment” show hematite increase between 500°C and 1000°C, which is quite similar to LETSCH AND NOLL (1983) showing an increase of hematite between 500°C and 900°C, followed by a decrease over 900°C. It also seems to show spinel from 600°C up, but the superposition of its main peak (313-peak) with the (110) peak of hematite implies to take this

temperature of formation with precautions, because only MAGGETTI (1982) describes spinel between 500° and 700°C, this latter being the “normal” forming temperature in the literature.

### 6.5.4 Mineralogy and estimation of the firing temperatures

The X-ray diffractograms of every studied sample are presented in Appendix 5; Appendix 6 lists the mineralogy observed in each diffractograms.

In order to simplify, we will now consider that all the yellowish-beige samples had time to completely re-oxidise, whereas all the plain black and plain grey sherds were fired in a completely reducing atmosphere. Even if we know that this fact is an approximation (the reduction indexes of these samples do not correspond exactly, see 6.5.2), it will permit to suggest an approximate firing temperature for these ceramics.

Therefore, the appendix 7B and the “306 experiment”, both resulting of oxidising firings, will be used to determine a firing temperature for the yellowish-beige sherds of colour group 1 (JB016, JB019, JB022, JB032, JB037, JB119, JB134, JB149, JB174, JB175, JB190).

In these eleven samples, two mineralogical associations (MA) were determined, with quartz, K-feldspar, plagioclase and illite always present (Table 6.3):

<table><caption>RE-OXIDISED SAMPLES</caption><thead><tr><th>Min. Assoc.<br>Yellow-beige</th><th>MA1</th><th>MA2</th></tr></thead><tbody><tr><th scope="row">Quartz</th><td></td><td></td></tr><tr><th scope="row">K-feldspar</th><td></td><td></td></tr><tr><th scope="row">Plagioclase</th><td></td><td></td></tr><tr><th scope="row">Illite</th><td></td><td></td></tr><tr><th scope="row">Chlorite</th><td></td><td></td></tr><tr><th scope="row">Hm, Sm, Cc,<br>Dol, Amph</th><td></td><td></td></tr><tr><th scope="row">Firing temp.</th><td>&lt; 550°C</td><td>550°C - 950°C</td></tr><tr><th scope="row">n</th><td>2</td><td>9</td></tr></tbody></table>

<table><caption>**Table 6.3:** The observed mineralogical associations of colour groups 1 and 2 and their inferred firing temperatures and predominant atmosphere of firing. Min. Assoc.: Mineralogical association, Colour gr.: Colour group; Firing temp.: Firing temperature (for details see text); n: number of samples; Hm: hematite, Sm: Smectite; Cc: Calcite; Dol: Dolomite; Amph: Amphibole.</caption><caption>REDUCED SAMPLES</caption><thead><tr><th>Min. Assoc.<br>Grey and black</th><th>MA3</th><th>MA4</th><th>JB105</th></tr></thead><tbody><tr><th scope="row">Quartz</th><td></td><td></td><td></td></tr><tr><th scope="row">K-feldspar</th><td></td><td></td><td></td></tr><tr><th scope="row">Plagioclase</th><td></td><td></td><td></td></tr><tr><th scope="row">Illite</th><td></td><td></td><td></td></tr><tr><th scope="row">Chlorite</th><td></td><td></td><td></td></tr><tr><th scope="row">Hm, Sm, Cc,<br>Dol, Amph</th><td></td><td></td><td></td></tr><tr><th scope="row">Firing temp.</th><td>&lt; 600°C</td><td>600°C - 700°C</td><td>&gt; 700°C</td></tr><tr><th scope="row">n</th><td>16</td><td>30</td><td>1</td></tr></tbody></table>
MA1: Mineralogical association with chlorite, i.e. fired below 550°C, with or without hematite, smectite, calcite, dolomite and amphibole, containing two samples (JB119, JB134).

MA2: Mineralogical association without chlorite, i.e. fired between 550°C and 950°C (temperature of illite vanishing), with or without hematite, smectite, calcite, dolomite and amphibole, containing nine samples (JB016, JB019, JB022, JB032, JB037, JB149, JB174, JB175, JB190).

In the mixed group composed of the black sherds (colour group 2) and the grey sherds of colour group 1, appendix 7C (reducing atmosphere) was used to propose a firing temperature. Except for JB105 that was fired above 700°C (illite vanished), all the samples contain quartz, K-feldspar, plagioclase and illite and distribute into two mineralogical associations (MA, Table 6.3):

MA3: Mineralogical association with hematite, with or without smectite, chlorite, calcite, dolomite and amphibole. As presented in LETSCH AND NOLL (1983), hematite disappears in reducing atmosphere at 600°C. Hence, the samples containing hematite were fired below 600°C. This group contains 16 samples (JB012, JB017, JB018, JB020, JB086, JB143, JB145, JB150, JB158, JB159, JB162, JB164, JB166, JB167, JB178, JB180). JB012 and JB020 contain extra apatite.

MA4: Mineralogical association without hematite, i.e. fired above 600°C and 700°C (temperature of illite vanishing), with or without smectite, chlorite, calcite, dolomite and amphibole, containing 30 samples (JB001, JB003, JB006, JB011, JB029, JB046, JB047, JB065, JB072, JB074, JB100, JB112, JB113, JB115, JB116, JB118, JB120, JB147, JB148, JB153, JB169, JB171, JB173, JB177, JB181, JB183, JB185, JB186, JB187, JB189). JB065 contains extra magnetite and JB147 contains extra apatite.

JB105 contains quartz, K-feldspars, plagioclase, calcite and dolomite, but no illite. This sample was fired over 700°C.

Because the mineralogical associations depend on the temperatures reached, on the firing atmosphere, on the mineralogy of the clay, but also on the duration of the peak temperature as well as on the granulometry of the matrix and temper, these associations are strongly dependent on the clay used. The papers presenting reducing atmosphere firings (LETSCH AND NOLL, 1983; MANIATIS ET AL., 1983; HERZ AND GARRISON, 1989;

MURAD AND WAGNER, 1989) do not completely correspond to the mineralogy of the clays used in Arbon Bleiche 3, and the results of the firing temperatures shall therefore be considered with precautions.

On 58 ceramics (colour groups 1 and 2), 3% were fired below 550°C and 28% below 600°C. 52% were fired between 600°C and 700°C and 16% between 550°C and 950°C. One other sample (2%, JB105) was fired above 700°C.

These firing temperatures are in accordance with the common ceramic firing activities in the Neolithic and correspond well to an open fire; they also conform to the literature.

The material of colour groups 3, 4 and 5 (banded sherds) were fired in a reducing atmosphere, followed with complicated cooling processes wavering between oxidising and reducing atmospheres. Therefore, it is not possible to properly estimate the firing temperature reached by these sherds, due to a complete absence of experiments in such complex cases. The only thing we can prove is the presence of illite in each sample, except for JB002. Hence, whatever the cooling was, these samples were not fired at much higher than 700°C, the temperature of disappearance of illite in a reducing atmosphere. Diopside and gehlenite were detected in only one sample, JB002, which was fired over 800°C (small bubbles are present in the matrix and show an over-firing of the sample).

The clays used to manufacture the ceramics from Arbon Bleiche 3 surely contained, as JB304 (Fig. 6.8), some smectites (illite/smectite or montmorillonite for example), chlorite, illite, quartz, K-feldspar, plagioclase but no calcite.

The ceramics can contain secondary minerals such as smectite and calcite. As described in the literature (see e.g. MAGGETTI, 1979; HEIMANN AND MAGGETTI, 1981; VELDE, 1995) smectite often reform by rehydration during burial. Small grains of calcite or dolomite (undifferentiated in the thin sections) are often observed in the fractures of the sherds as neo-crystallised grains. Both also reform during burial. Hence, these both minerals were not used to determine the firing temperatures.

Conversly, chlorite is not a secondary mineral because it does not appear during burial under normal conditions of pressure and temperature. As specified in MAGGETTI ET AL. (1990, 102), chlorite is often a primary mineral, because it is found in the superficial