..
P.S.Quinn: Behaviour of nannofossils during the firing ..... , p. 31 - 32.

Journal of Na1moplankton Research, 21, l , 1999.

A NOTE ON THE BEHAVIOUR OF CALCAREOUS
NANNOFOSSILS DURING THE FIRING OF CERAMICS
Patrick Sean Quinn, Dept. ofArchaeology & Prehistory, University ofSheffield, UK

Abstract: Firing of ceramics during manufacture deleteriously affects calcareous nannofossil assemblages.
Determining the provenance of archaeological ceramics from such assemblages can, therefore, beproblematical, and it is important to have an understanding of the behaviour of tl1is calcareous component
during firing. The experiments outlined here show iliat calcareous nannofossil assemblages are degradedby heating above 600•C, and can be completely destroyed at temperatures of over 800•C.

Introduction
Calcareous nannofossil assemblages in archaeologicalceramics can be altered by several processes (Table I), of
which one of the most important is firing. In order todetennine the effects of firing on the nature of calcareous
nannofossil assemblages in archaeological ceramics,
experiments have been conducted on material from theAlbian Gault Clay Formation, concentrating on the effects
produced by three variables: the maximum temperatureof firing, the length of firing, and the firing atmosphere.

attained by ancient kiln firings.
Calcareous nannofossil smear-slides were prepared fromthe raw Gault Clay, a processed but unfired briquette, andall of the fired samples.

Table l: Processes which can affect calcareous nannofossil
assemblages in archaeological ceramics.

Results
Quantitative calcareous nannofossil analysis of smearslides prepared .from the fired briquettes indicated a
progressive decrease in the overall abundance, diversity
and preservation of the Gault Clay assemblages (Figure 1).
Calcareous nannofossils were found to survive a maximum
firing temperature of8000C in an oxidising atmosphere and700°C in a reducing aUnosphere, after which all briquettes
were barren and low in calcite. Increasing the length ofthefiring process was found to have a similar effect, although
this was much less severe.
By recording the relative abundances of thevarious taxa and structural groups of calcareous
nannofossils in the fired Gault Clay briquettes, it waspossible to document a progressive change in thecomposition ofthe assemblages. Tltis will be presented indetail elsewhere (Quinn et al., in prep.), but generally
consists of an increase in the relative abundance of
Watznaueria species (imbricating placoliths), accompanied
by a decrease in the relative abundances of all other taxa,
with increasing temperature and length of firing. These
patterns are probably related to several factors, including
variations in the physical resilience of the different groupsof calcareous nannofossils to the process of firing, andthe degree of ease with which they can be identified fromsmall fragments. ·Material and methods
The Gault Clay, which was collected at Strouanne, NFrance, was chosen because of its abundant, wellpreserved calcareous nannofossil assemblages, as well as
its suitability as a raw material for the manufacture ofceramics. Several kilogrammes of Gault Clay, procured
from a short (-IOcm) interval, were left to dry, thencrushed, sieved, mixed with water and fashioned into
equidimensional briquettes. The dried briquettes werefired in either air (an oxidising atmosphere) or in a reducing
atmosphere (4% H2 by volume) for 1 hour, at maximum
temperatures of600, 700, 800, 900, 1000 and 1100°C. In
addition, briquettes were fired for a duration of one, two,three and four hours at a maximum temperatureof6000C, inan oxidising aunosphere. These temperatures were chosenin accordance with the range of temperatures which wereConclusions
Calcareous na1mofossil assemblages can be subjected toexcessive heat in several other situations, including thecasting of bronze statues (Fiorentino, 1998), and it isimportant to have an understanding of the way in whichassemblages can be affected if the nannofossils are to be
used to detennine the provenance (stratigraphical andgeographical) ofthe material.
The experiments wltich are briefly outlined above
indicate that calcareous nannofossil assemblages andindividuals are degraded by heating above 600°C, and canbe completely destroyed at temperatures of800-9000C. The
exact process wltich leads to the destruction of calcareous
nannofossils during the firing of ceramics is suspected tobe the chemical decomposition of calcite. Tltis will be fully
discussed elsewhere (Quinn et al., in prep.).

1.
CONTAMINATION DURING CLAYPROCUREMENf.
2UNINTENTIONAL CONTAMINATIONDURING CLAYPREPARATION AND STORAGE.
3. INTENTIONALCLAYMIXING.
4.
ALTERATION OF CALCAREOUS NANNOFOSSILASSEMBLAGES DURING FIRING.
5.
POST-FIRING AL1ERAI10N OF CALCAREOUS
NANNOFOSSIL ASSEMBLAGES AS A RESULT OF
USAGE:
a. cooking;b. storage.
6.
ALTERATION AND CONTAMINATIONDURING BURIAL.
7. ALTERATION AND CONTAMINATION AFTEREXCAVATION AS A RESULT OF POOR SAMPLE
CURATION.

31f,rJournal ofNannoplankton Research, 21 , I, 1999.

PS.Quinn: Behaviour of nannofossils during the firing..... , p. 31 - 32.

Refe1·ences
Fiorentino, A. 1998. The potential of nannofossil analysis applied
to archaeological studies: the case of the Riace's bronzes.
Journal ofNannop/ankton Research, 20(2): 101-103.

Quinn, P.S., Day, P.M. & Kilikoglou, V. In prep. Investigations
into the behaviour ofcalcareous nannofossils during the firingof ceramics. For submission to Archaeometry.

Figure 1: SEM illustrations of the degradation of calcareous na1mofossils during the experimental firing of Gault Clay briquenes (scale bars= 10~): (a) broken surfaces of Gault Clay briquettes fired at 600•C; and (b) 800°C32