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# Analysis of early Iron age glass beads (8th to 7th c. BC) from the Tsaishi necropolis (Georgia)

Gvantsa Vachadze, Bernard Gratuze

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Gvantsa Vachadze, Bernard Gratuze. Analysis of early Iron age glass beads (8th to 7th c. BC) from the Tsaishi necropolis (Georgia). Journal of Archaeological Science: Reports, 2025, 62, pp.105066. 10.1016/j.jasrep.2025.105066. hal-04974650

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# Analysis of early Iron age glass beads (8th to 7th c. BC) from the Tsaishi necropolis (Georgia)

Vachadze Gvantsaª, Gratuze Bernardᵇ,ᶜ

## ARTICLE INFO

**Keywords:**

Glass Beads

Colchis

Early Iron Age

LA-ICP-MS Chemical Analysis

High boron and lithium glass

Positive cerium anomaly

## ABSTRACT

We present the analytical results obtained by LA-ICP-MS from a set of 38 glass beads of various colours dating from the 8th to the first half of the 7th century BCE, found at Tsaishi cemetery, located in the central area of historical Colchis (Georgia).

Through the comparison with published analytical data of coeval, earlier and later glass samples, the aim of this study is to investigate the provenance of Tsaishi assemblages in order to highlight the cultural influences and trading networks of the Colchis community between the 8th and the 7th centuries BC.

Tsaishi glass beads predate previously studied glass beads from Brili necropolis, located in the mountainous part of Colchis (North-west Georgia). In contrast to the compositions of the Brili glasses, the measurements of the Tsaishi glass beads do not allow for the identification of the well-established Iron Age compositional groups. Furthermore, in contrast to the other Early Iron Age sites, they do not appear to indicate the presence of typical Egyptian or Syro-Palestinian natron glass productions. Although our assemblage shows considerable compositional variability, it highlights the existence of a new group of glass recently identified in Italy and characterised by a positive cerium anomaly, as well as a group of high boron and lithium glasses. However, despite the large variation in contents for minor elements, colourless and purple glass are all part of the same group.

Comparison with other Early Iron Age glass studies points to a fairly complex situation, probably due to small scale production of raw glass and glass beads, the multitude of production sites and the diversity of recipes used by glass workers at the beginning of the first millennium B.C.

## 1. Introduction

This study deals with the glass bead assemblages excavated between 2003 and 2007 years in N1 and N2 collective burial pits at Tsaishi Cemetery. Collective burials are characteristic of the Colchis region during late Bronze and early Iron Ages and are mainly located in its central area (Fig. 1). Due to their large-scale, these cemeteries provide rich series of archaeological materials, such as bronze, Iron, ceramic and beads made of glass and different minerals and best reflect the life of the region. All the studied Colchian collective burial pits are characterised with amorphous cultural layers that consist of human skulls, limb bones, teeth, and various types of inventory. Due to the irregular arrangement of these materials it is accepted that collective pits saw multiple uses (Papuashvili, 2000). In the light of these circumstances, the general chronology of the Tsaishi cemetery is reckoned to fall between the first half of the 8th and the first half of the 7th century BCE (Papuashvili et al., 2015).

Archaeological records on glass indicate that before the 1st millennium BC vitreous materials are registered in small quantities in Colchian Culture. From the beginning of the 1st millennium BC opaque and translucent glass started to appear in the context of Colchian collective graves. One of the initial locations for the accumulation of these glass beads is Tsaishi Cemetery. Some of these glass beads find parallels in Colchis, while others, such as anthropomorphic and zoomorphic samples have no local analogues morphologically (Vachadze, 2023).

In the absence of a local tradition, the sudden emergence of diverse glass bead types in shape and colour raises concerns about their origins or trade channels. In this regard, integrating the stylistic and chemical studies of Tsaishi samples aim to provide a deeper understanding of the nature of these glass products and create a new foundation for learning about their production sites and trade/exchange ties between Colchis and other regions during the Iron age.

<footnote>ªGeorgian National Museum, 3 Rustaveli Avenue, Tbilisi, Georgia</footnote>

<footnote>ᵇIRAMAT-CEB, UMR 7065, CNRS/Orleans University, Orleans, France</footnote>

<footnote>* Corresponding author.</footnote>
<figure><img src="image_4.png" /><figcaption>**Fig. 1.** Colchian archaeological sites from Georgie cited in the text: 1. Tsaishi 2. Brili 3. Ergeta 4. Pichvnari.</figcaption></figure>

## 2. Studied corpus

An early group of glass beads was found in burial pit N2 and dates to the first half of the 8th century BCE or more generally, the first quarter of the 1st millennium BC (Papuashvili, 2015). The following chronological groups of glass were found in burial pit N1 dating back to the second half of the 8th and the first half of the 7th century BCE. Overall, compared to jewellery made of different minerals, glass beads are in minority. The quantity of glass beads found in the burial pits is nearly comparable, however the glass assemblage from pit N2 has a greater range of shapes and colours than the group from pit N1.

38 Translucent and opaque glass samples from Tsaishi have been selected based on colour and shape to represent all types of glasses that have evidenced in Tsaishi necropolis (Fig. 2). Twenty-one beads came from pit N2 with the remaining 17 from pit N1. The samples incorporate beads and pendants. (Supplementary materials, Table S1). Except for the one eye bead (4145 A) from pit N2, all the selected samples are mono-chrome. Uncharacteristic types are zoomorphic (fish?) (3842) and anthropomorphic (3849) bead fragments also found in pit N2 and bird shaped pendant (570) found in pit N1. All of the remaining beads are representations of simple geometric shapes, which form seven main groups. The absolute majority of these geometric forms are represented by spherical beads (569.3.a; 569.3.b; 569.3.c; 569.3.e; 569.4.c; 569.4.d; 570.2.a; 570.2.c; 4146d; 4146e). The next largest group comprises annular shapes (569.3.d; 569.4.a; 4146c; 4141a; 4146a; 4142a; 567a; 569.4.b; 4164a; 4164d; 4164b). Two beads are in biconical (4141b; 4142b), melon (570.2.b; 4145b) and segmented (4145c; 4145d) shapes and single beads in ring (4142c) and conical (567b) shapes. The rest of the samples does not allow us to precisely determine their form (4143; 569.2.a; 569.2.b; 4163a; 4164c)

The 38 studied glass beads from Tsaishi are classified into 6 main groups according to their colours: amber (4), black-appearing (4), blue/green/turquoise (12), natural tint/colourless (8), natural tint/deeply coloured (4) and purple (6).

Annular and spherical glass beads find analogues in Colchian collective burial pits, for example at Ergeta (Papuashvili et al., 2022), Mukhurcha (Eliava, 1987) or Ureki (Mikeladze, 1985) cemeteries. Similarities can be seen also in the archaeological finds of Eastern Georgia (Abramishvili et al., 1980; Gambasidze, 2001; Kalandadze, 1982; Lekashvili, 1999).

Discoveries of translucent spherical beads are characteristic beyond Colchis, namely in Urartian, Persian, Aegean, Campanian and Etrurian contexts, as well as north of the Alps (Spaer, 2001; Triantafyllidis, 2002). Bird shaped glass beads are widespread in the Oriental, Aegean and eastern Mediterranean world, reaching as far as Italy (Spaer, 2001; Huber, 2003; Koch, 2011). Appearance of these new type translucent spherical beads and bird shaped pendants seem to start from the 9th century BCE in different regions and chronologically directly match with

the Tsaishi findings.

There is yet no archaeological evidence of a glass making facility or its secondary workshop in late Bronze or Iron Age Colchis (Vachadze, 2023). However, two stone bead workshops in Central Colchis dating from the 11th to 6th centuries BC have yielded overall sixteen glass beads and one anthropomorphic pendant (Apakidze, 1991; Apakidze, 2001; Gogadze et al., 2010). Considering the fact that the mountainous zone of Colchis has been confirmed to contain deposits of quartz sand, suitable for glass production and other necessary impurities, such as copper, cobalt, manganese (Kapanadze et al., 2004) and antimony (Gobejishvili, 1952; Degryse et al., 2020), the existence of glass secondary workshops or its production should not be excluded, adding the fact that in these periods Colchis already owned a mastery of smelting/firing technologies related to metal production, which is confirmed by discoveries of hundreds of crucibles throughout the region (Papuashvili, 2003; Inanishvili and Jibladze, 2019).

Given the striking stylistic similarities between Tsaishi glass beads and glasses found in remote areas, a more accurate localization of these parallels is necessary. LA-ICP-MS analysis below may provide more answers to these issues.

## 3. Analytical methods

38 glass beads were analysed using LA-ICP-MS representing 75 analytical points (repeated analysis).

This method requires no sample preparation and is particularly well adapted to composite or decorated glass objects (Gratuze, 2016). The glass objects are placed inside an ablation cell (Resonetics S155, 10 x 15 cm), where a micro-sample, invisible to the naked eye (diameter < 100 µm), is extracted by the laser beam. This sampled material is then carried to the plasma torch of the mass spectrometer by an argon/helium gas flow (1 l/min Ar + 0.65 l/min He) where it is dissociated and ionised by the high temperature of the plasma (8000 °C). The different glass constituents are separated according to their mass/charge ratios by the double focussing mass spectrometer and quantified by the electronic detector (a secondary electrons multiplier or a Faraday cup according to the ion beam intensities).

The instrumentation employed consists of a Resonetics M50E excimer laser working at 193 nm coupled with a Thermo Fisher Scientific ELEMENT XR mass spectrometer (Fig. S1).

The excimer laser was operated at 5 mJ with a repetition rate of 10 Hz. The beam diameter was adjusted from 40 µm to 100 µm to avoid saturation from elements such as manganese, copper, tin, antimony or lead. A pre-ablation time of 20 s was set in order to eliminate the transient part of the signal which was then acquired for 27 s corresponding to 9 mass scans from lithium to uranium (the signal in count/second is measured in low resolution mode for 58 different isotopes). Between one and three ablations were carried out per bead and depending on the colours. If surface contamination was observed a second or a third ablation was carried out at the same place. Measurements reflecting intensive corrosion processes were rejected.

Calibration was performed using 5 reference glass materials; NIST610, Corning B, C and D, and APL1 (an in-house standard glass with composition determined by Fast Neutron Activation Analysis which is used for chlorine quantification), which were run periodically to correct for a potential drift. The standards are used to calculate the response coefficient (k) of each element (Gratuze, 2016). The net signals measured for each isotope are then normalised to $^{28}$Si, the internal standard, and corrected for their isotopic abundance, their response coefficient and their main oxidation state in order to calculate the concentration of each element expressed as oxide weight percentages.

The detection limits range from 0.1 to 0.01 % for major elements and from 20 to 500 ppb for others.

In order to validate the obtained concentration results, glass reference standards Corning A and NIST612 are regularly analysed as unknown samples throughout the analytical sequence. The average values
<figure><img src="image_5.png" /><figcaption>Fig. 2. Set of the 38 studied glass beads from the Tsaishi Necropolis.</figcaption></figure>

obtained during the analysis for these glasses are presented in the table of results and agree within 5 to 10 % with the certified ones (Table S2).

# 4. Results

## 4.1. Main glass constituents: Sands and fluxes

All the studied Tsaishi's glass are siliceous soda/soda-lime/soda-alumina-lime glass. However, the obtained results (Table S3) show considerable variability of contents and continuous variation of composition for the main minor oxides (MgO 0.26 to 4.9%; Al₂O₃ 0.17 to 9.4%; P₂O₅ 0.03 to 0.97%; K₂O 0.31 to 5.8% and CaO 0.45 to 10.7%). This feature does not allow to identify clearly the well-established compositional groups such as Egyptian or Syro-Palestinian natron glasses or Mesopotamian soda plant ash glasses (Fig. 3) which usually

characterise Iron Age assemblages. In order to identify specific productions within our corpus, a less traditional approach will be adopted. This approach will consider not only the main minor elements but also the most relevant trace elements.

According to their MgO, K₂O and P₂O₅ contents (MgO < 1%; K₂O < 1% and P₂O₅ < 0,1%), three of the glass beads were without any doubt produced with a mineral soda flux (Low Mg K glasses), however, their chlorine contents (Cl < 0.6%) appear to be lower than that usually encountered in well-identified production such as Egyptian and Syro-Palestinian natron glasses.

Among the 35 remaining glass beads, which have higher MgO, K₂O and P₂O₅ contents, seven are characterised by high contents of lithium and boron (High Li B glasses) (Fig. 4). Within this group, two of the glasses have lithium and boron contents similar to those of the glass from Brili and Pichvnari (Vachadze et al.; Shortland and Schroeder, 2009) and
<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Distribution of contents of the main minor oxides, in the different glass groups, according to their minimum, first quartile, third quartile and maximum values.</figcaption></figure>

some from Hasanlu (Lankton, forthcoming; unpublished data) (Li₂O 0.012 to 0.015%; B₂O₃ 0.57 to 0.59%), two others have higher lithium and boron contents more similar to those of the glass beads from Sardis (Van Ham-Meert et al., 2019) (Li₂O 0.013 to 0.015%; B₂O₃ 0.93 to 1.15%), while the last three are characterised by lower boron and lithium contents (Li₂O 0.0017 to 0.0062%; B₂O₃ 0.31 to 0.43%), which are

similar to those of the majority of Italian glass beads published by Conte (Conte et al., 2016).

A particular group of eighteen glass beads show surprisingly high Ce/La ratios (High Ce/La glasses) (Fig. 5 and Figs. S2 and S3). This type of glass was observed by Conte (Conte, 2015a, p. 161-162; Conte, 2015b) and Yatsuk (Yatsuk et al., 2024a) in Italian glass beads from
<figure><img src="image_7.png" /><figcaption>Fig. 4. Distribution of the studied glass according to their content of lithium (Li₂O) and boron (B₂O₃) oxides. Comparison with glass from Brili (Vachadze et al.), Sardis (Van Ham-Meert et al., 2019), Italian sites (Conte et al., 2016) and Hasanlu (Lankton, forthcoming; unpublished data). For Sarno and Cuma (Conte et al., 2016), lithium values were not published, they are given in the supplementary material in Tab. S4.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 5. Distribution of the studied glass according to their content of lanthanum (La₂O₃) and cerium (CeO₂) oxides. Comparison with glass from different Italian sites (Conte et al., 2016; Conte et al., 2019; Yatsuk et al., 2024a). For Sarno and Capua (Conte et al., 2016), lanthanum and cerium values were not published, they are given in the supplementary material in Tab. S4.</figcaption></figure>

different sites dating from the 8th-7th centuries BC and by Franjić (Franjić, 2019) in early Iron Age Croatian glass beads from Nadin and Picugi.

The ten remaining glass beads are mainly characterised by their high magnesia and potash contents and their variable phosphorus contents

(High Mg K glasses), (Figs. 3, 6 and 7).

It should be noted (Fig. 3) that the 'High Li B' group of glasses has the lowest lime contents, while the 'High Ce/La' group has the highest. The other two groups, 'low Mg K' and 'high Mg K', have intermediate contents.

It was also observed that while some of the colours are present in several glass groups (Table 1), natural tint/colourless and purple are only represented in the high Ce/La group.

### 4.1.1. Low Mg, K, soda-lime glass group (Mineral soda)

Two amber and one black appearing glass represent a mineral soda glass. As noted above, the chlorine contents of these three glasses appear to be lower than those usually encountered in Egyptian and Syro-Palestinian glasses made with Egyptian natron supposed to originate from the Wadi Natrun deposits (Fig. 8), only a few glasses from Georgia (Tsaishi and Brili) and Italy show similar contents. This could indicate the use of different type of natron deposit, containing less chlorine, or the use of melting processes that limit the insertion of chlorine into the glass. However, we are aware that there are far fewer analyses of natron glass from the Early Iron Age than from the later Hellenistic and Antiquity periods. Furthermore, the variability of minor elements contents within these early glasses is not yet fully understood. At this stage, therefore, it is difficult to establish whether or not these glasses come from early Egyptian or Syro-Palestinian productions.

The two amber glass exhibit particularly high contents of silica (SiO₂ 73.8–74.7 %) and low contents of alumina (Al₂O₃ 0.17–0.18 %), tita-nium (TiO₂ 156–169 ppm) and zirconium (ZrO₂ 10–12 ppm) oxides (Fig. 9). These concentrations point to the uses of fairly pure quartz by the glassmakers. These contents are identical to those exhibited by three amber glass beads from Francavilla Marittima (FM5a, 10a and 11a: SiO₂ 73.6 to 76 %; Al₂O₃ 0.14 to 0.23 %; TiO₂ 130 to 190 ppm; ZrO₂ 10 to 11 ppm) (Conte et al., 2019) and one from Verucchio (Ivana Angelini, personal communication). It highlights the common origin of these glass beads, but again, this distinguishes them from the more typical Egyptian and Syro-Palestinian natron glass productions.

### 4.1.2. High Mg, K, soda-lime glass group (Soda plant ash)

Seven blue/green/turquoise and three natural tint/deeply coloured glasses with the highest potash and phosphoric oxide content amongst our samples have been produced from a soda-rich plant ash Figs. 6 & 7) (Reade et al., 2009; Oikonomou and Triantafyllidis, 2018). Three sub-

<figure><img src="image_9.png" /><figcaption>Fig. 6. Distribution of the studied glass according to their chemical groups, colours and contents of soda (Na₂O), lime (CaO), magnesia (MgO), potash (K₂O) and phosphorus pentoxide (P₂O₅).</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Fig. 7. Distribution of the studied glass according to their reduced content of phosphorus pentoxide (P₂O₅) vs magnesia (MgO) and potash (K₂O).</figcaption></figure>

<table><caption>**Table 1**
Distribution of glass colours among the different chemical glass groups.</caption><thead><tr><th></th><th>Natural tint colourless (8)</th><th>Natural tint/deeply coloured (4)</th><th>Purple (6)</th><th>Amber (4)</th><th>Black-appearing (4)</th><th>Blue/green/turquoise (12)</th></tr></thead><tbody><tr><td>High Li B (7)</td><td></td><td></td><td></td><td>1</td><td>3</td><td>3</td></tr><tr><td>High Ce/La (18)</td><td>8</td><td>1</td><td>6</td><td>1</td><td></td><td>2</td></tr><tr><td>Low Mg K (3)</td><td></td><td></td><td></td><td>2</td><td>1</td><td></td></tr><tr><td>High Mg K (10)</td><td></td><td>3</td><td></td><td></td><td></td><td>7</td></tr></tbody></table>

<figure><img src="image_11.png" /><figcaption>Fig. 8. Distribution of the low Mg K glass according to their chlorine and sodium oxides contents. Comparison with natron glasses from Brili (Vachadze et al.) and from different Italian sites (Conte, 2015a, Conte et al., 2016; Conte et al., 2019 and unpublished data on Early Iron Age natron Italian glass beads).</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 9. Distribution of the low Mg K glass according to their zirconium and titanium oxides contents. Comparison with natron glasses from Brili (Vachadze et al.) and from different Italian sites (Conte, 2015a, Conte et al., 2016; Conte et al., 2019 and unpublished data on Early Iron Age natron Italian glass beads).</figcaption></figure>

groups can be distinguished within this group when the levels of various minor and trace elements (Mg, Al, P, Ti, V, Cr, Mn, Zn, Rb, Zr, Ba, REE and Th) are taken into account (Fig. 10 a to d). The two sub-groups characterised by the highest alumina and lowest magnesia contents are similar to the high Mg, K, P soda-lime glass (Soda plant ash) identified at Brili (Vachadze et al.). However, the corpus studied is too small to know whether this difference is due to the presence of glass groups of different origins or whether it simply reflects the variability of compositions within a single group.

As it was observed at Brili, with the exception of one blue-green glass bead from the Bulgarian necropolis of Dren-Delyan (Tzankova and Mihaylov, 2019) and some unpublished data on Early Iron Age Iranian glasses from Marlik and Amlash and Indian glasses from Hatt (Lankton, unpublished data), all the other published Early Iron Age plant ash glasses exhibit higher magnesia than potash content (MgO/K₂O > 1) and low phosphoric oxide content (P2O5 < 0.5 %) (glass group defined as classical “Mesopotamian plant ash glass”, Oikonomou and Triantafyllidis, 2018; Henderson et al., 2018; Brill, 1999; Stapleton, 2003; Reade et al., 2005; 2009; Reade et al., 2012). The third sub-group (4142c and 569.4.a&b) has lower alumina, and phosphorus contents and higher magnesia contents and resembles the classical “Mesopotamian plant ash glass” such as those identified in Rhodes (Oikonomou and Triantafyllidis, 2018) and in Italy (Conte, 2016 & 2018), but they seem to contain a little more potash (Fig. 10b).

However, it seems that to date, sub-groups with a high Mg K P content (MgO/K₂O < 1 and P2O5 > 0.5 %) have not been identified outside Anatolia and the Caucasus, which could indicate an eastern Mesopotamian origin for these soda-lime glasses based on plant ash.

### 4.1.3. High lithium and boron glasses (High Li B glass group)

In this group we find one amber-coloured glass, three black-appearing glasses and three blue/green/turquoise samples.

Within this group, the lithium and boron contents show a fairly large distribution (Li₂O 17 to 152 ppm; B₂O₃ 0.31 to 1,15 %). This variability is wider than the one observed in Brili and Pichvnari (Li₂O 134 to 349 ppm; B₂O₃ 0.27 to 0.84 %; Shortland and Schroeder, 2009; Vachadze et al.), but is almost identical to that reported by Conte for the Italian
<figure><img src="image_13.png" /><figcaption>Fig. 10. Distribution of the high Mg K glass according to their a) alumina and magnesia contents, b) potash and magnesia contents, c) magnesia and phosphoric oxide contents, d) barium and zirconium contents. Comparison with plant ash glasses from Brili (Vachadze et al.), from Rhodes (Oikonomou and Triantafyllidis, 2018) and Italy (Conte et al., 2016; Conte et al., 2019).</figcaption></figure>

beads from Cuma and Sarno (Li2O < 1dd to 174 ppm; B2O3 0.21 to 1.43 %; Conte et al., 2016). It could thus be hypothesised that these significant variations in lithium and boron contents are due to the variability of lithium and boron in the mineral deposit used as soda flux rather than the use of different mineral deposits. The considerable scatter in lithium concentrations may also be explained by the volatility of this element.

Among our corpus, black-appearing glasses have the lowest contents of lithium, boron and magnesium, while the blue/green/turquoise glasses have the highest (Fig. 4). The glasses from that group have also the lowest lime content of the studied assemblage (Figs. 3 & 6). The compositional variability seen at Brili for some other minor oxides is not present at Tsaishi (MgO 1.5 to 6.4 % at Brili and 0.26 to 2.9 % at Tsaishi; Al₂O₃ 0.62 to 10.5 % at Brili and 1.0 to 2.4 % at Tsaishi; K₂O 0.97 to 4.2 % at Brili and 0.4 to 1.6 % at Tsaishi; CaO 2.3 to 8.8 % at Brili and 0.45 to 4.3 % at Tsaishi). The Tsaishi assemblage has lower contents for all these oxides, which could be the result of the use of purer raw materials. These differences could also be due to the smaller size of the Tsaishi corpus (7 beads and 7 different glasses) compared to that of Brili (34 beads and 45 different glasses).

This glass group, which has already been identified in Georgia at Pichvnari and Brili (Shortland and Schroeder, 2009; Vachadze et al.), is increasingly common among late Bronze Age and early Iron Age glass objects throughout the Mediterranean Basin (Brill, 1999; Plouin et al., 2012; Cherel and Gratuze, 2018; Varberg et al., 2015; Mildner et al., 2018; Dussubieux et al., 2018; Henderson et al., 2018; Conte et al., 2016; Van Ham-Meert et al., 2019). As pointed out in several studies, this group of glass was probably made with some mineral soda flux rich in boron and lithium, probably originating from Anatolia or the Caucasus (Schibille, 2011; Dussubieux et al., 2018, Van Ham-Meert et al., 2019).

### 4.1.4. Glass with high cerium/lanthanum ratios (High Ce/La glass group)

The largest group of the Tsaishi bead corpus (18 beads of 38) has unusually high cerium contents. It includes all the colourless (8) and purple (6) glass beads, as well as two blue/green/turquoise, one amber and one deeply coloured glass beads. As a group, it is relatively homogeneous (Fig. 3) characterised by high lime (CaO 5,6 to 10,7%) and low alumina contents (Al₂O₃ 0.4 to 1.1 %). It has moderate magnesia (MgO

1,6 to 4.9 %), potash (K₂O 0,8 to 3,4%) and phosphorus contents (P₂O₅ 0.1 to 0.4 %). Their phosphorus contents are similar to those of the high Li B glasses (P₂O₅ 0.04 to 0.5 %) for which the use of a mineral soda flux is assumed. Their potash and phosphorus contents are also lower than those measured for the high Mg K glass (K₂O 2.9 to 6 %; P₂O₅ 0.15 to 1.0 %, av. 0.5 %).

A high Ce glass group has been isolated by Conte (Conte, 2015a & 2015b; Conte et al., 2016; Conte et al., 2019) in glass beads from Capua, Sarno and Francavilla Marittima dating to the eighth/seventh centuries BC, and more recently by Yatsuk (Yatsuk et al., 2024a) among another early Iron Age Italian glass beads assemblage (Polledrara of Bisenzio, Caolino del Sasso di Furbara of Cerveteri, Caracupa necropolis near Sermoneta and Osteria dell'Osa necropolis near Gabii/Rome).

The unusual high Ce/La ratios exhibited by these glasses (Figs. S2 and S3) could indicate the presence of positive cerium anomalies in some of the raw materials used. Several approaches are used to calculate these anomalies represented by Ce/Ce* (Barrat et al., 2023; Zhang and Shields, 2022). In order to compare our data with those of Yatsuk where no Pr values were given, we choose to calculate the Ce/Ce* value by interpolating Ce* between La and Nd, using the following equation:

$$Ce/Ce^* = Ce_{CI} / (La_{CI}^{2/3} \times Nd_{CI}^{1/3})$$

where XCI represents the rare earth elements' contents normalised to chondritic values (Barrat et al., 2023).

The different glasses plotted in the diagram Ce/Ce* vs La/CI/Nd/CI (Fig. 11a) separate into four main groups. On the left of the graph, the dark blue glasses coloured with cobalt extracted from Egyptian alum (Conte et al., 2015b; Gratuze and Picon, 2005) differ clearly from all other groups due to their lower La/CI/Nd/CI ratios. The particular signature of these cobalt blue glasses is probably inherited from the cobalt ore originating from the Egyptian alum (Decree et al., 2015; Gratuze, on press).

All other glasses can be assigned to three groups based on their Ce/Ce* signatures. All samples with Ce/Ce* > 1.2 have a positive cerium anomaly and include the Tsaishi high Ce/La group and the high Ce glasses identified in Italy (Conte, 2015b; Yatsuk et al., 2024). A cerium
<figure><img src="image_14.png" /><figcaption>**Fig. 11.** A) ce/ce* and laCl/NdCl ratios of different glass groups. It is assumed that a Ce/Ce* value of 0.8–1.2 has only limited geological meaning and indicates the cut-off for a positive/negative anomaly, b) Comparison of the normalised lanthanum (LaCl) and cerium (CeCl) contents of the different glass groups, including glass from Brili (Vachadze et al.) and different Italian sites (Conte 2015a, Conte et al., 2016; Conte et al., 2019; Yatsuk et al., 2024a and unpublished data on Early Iron Age natron Italian glass beads). For Sarno and Capua (Conte et al., 2016), lanthanum and cerium values were not published, they are given in the supplementary material in Tab. S4.</figcaption></figure>

anomaly of Ce/Ce* between 0.8 and 1.2 has only limited geological meaning as it can be caused either by analytical or normalisation artefacts. Hence, almost all high Li B and high Mg K glasses, along with all Brili Syro-Palestinian glasses and some Brili Egyptian natron glasses in this Ce/Ce* range do not exhibit a cerium anomaly. Values of Ce/Ce* < 0.8 indicate that the glass have a negative cerium anomaly. This last group of glasses seems to comprise only Egyptian natron glasses and reflect clear mineralogical differences in the raw materials used to make a large part of Egyptian natron glasses compared to the raw materials used to make high Li B, high Mg K, low Mg K and Syro-Palestinian natron glasses. These glasses showing a negative cerium anomaly are plotted under the ‘normal’ curve (CeCl ≈ 0.74 x LaCl, Fig. 11b).

From a geological point of view, positive cerium anomalies are not common and tend to be associated with the mechanism of oxidative removal of tetravalent cerium by iron and/or manganese oxides. They can, however, be common features of alkaline, carbonate-rich and aerobic lake waters (Pourret et al., 2008). Positive cerium anomalies also

occur in hydrogenic oceanic and soil concretions (Vodyanitskii, 2012) and in some manganese or iron ores (Zhang and Shields, 2022). Important cerium positive anomalies have been identified in alkaline waters from Lake Van (Turkey) (Möller and Bau, 1993), in lateritic profiles at Akongo and Goyoum (Cameroon) (Braun et al., 1990) or in carbonate deposits at Doushantuo (Yangtze platform, South China) (Wu et al., 2019). According to published values for chondrite, mid-ocean ridge basalt (MORB), earth crust (upper crust UC, felsic lower crust FLC and mafic lower crust MLC) and meteorites, cerium to lanthanum ratios vary from 1.34 in meteorites (Anders and Grevesse, 1989) to 3 in MORB (McDonough and Sun, 1995). The Ce/La ratios are in the order of 2 for the continental crust, 1.7 for greywackes (sandstone), 2.3 for tonalite (igneous, plutonic rock) (Wedepohl, 1995), and 2.6 for chondrites (Anders and Grevesse, 1989; McDonough and Sun, 1995). The cerium to lanthanum ratios for the high Ce/La glasses from Tsaishi range from 2.4 to 6.5 (average 3.98), which are much higher than those encountered in most siliceous material present on Earth.
It should also be noted that the cerium-lanthanum curves are generally straight lines passing through the origin. In Figs. 5 and 11b, we can see that this is the case for most of the glasses that have no anomalies (Ce ≈ 1.9 x La or CeCl ≈ 0.74 x LaCl), but the straight line representing the group with a positive cerium anomaly does not pass through the origin (Ce ≈ 6.5 x La – 8 or CeCl ≈ 2.5 x LaCl – 13) and intersects the lanthanum axis at a value of around 1.2 ppm (Fig. 5). This particular feature may be due to the fact that the glasses with a positive cerium anomaly come from a mixture of two different sources of raw materials: a minor one (20 to 30 % of the batch) showing a large variability of Ce/La ratios with positive cerium anomaly and a major one (70 to 80 % of the batch), without anomaly, which would shift the origin towards positive lanthanum values.

The Figs. 5 and 11b also show the greater dispersion of points representing glasses with a positive cerium anomaly: this fits with the hypothesis of a large variability of Ce/La or CeCl/LaCl ratios within the potential source of raw material used to make these glasses.

Based on the above data, it seems therefore unlikely that the positive cerium anomaly was related to the silica source, but more probably that it was related to the lime, the flux sources or to some manganese or iron ore used by the glassworkers.

The high Ce/La glasses from Tsaishi were made with a relatively pure silica source low in mineral impurities such as alumina (Al₂O₃ 0.36 to 1.08 %), iron (Fe₂O₃ 0.29 to 0.76 %), titanium (TiO₂ 294 to 789 ppm) and zirconium (ZrO₂ 13 to 33 ppm). They contain variable amount of magnesia and potash (MgO 1.6 to 4.9 %; K₂O 0.76 to 3.4 %), fairly high amounts of lime (CaO 5.6 to 10.7 %), and variable amounts of manganese (MnO 0.02 to 1.1 %), which exclude the possibility that the positive cerium anomaly was caused by a manganese compound.

On the basis of these observations, we can hypothesise that glasses with a positive cerium anomaly were produced using an evaporitic deposit containing soda, lime, magnesia and potash. The positive cerium anomaly then derived probably from the alkaline waters that produced these deposits. The similar phosphorus contents of the high Li B and high Ce/La glasses (Figs. 3 and 7) as well as and the low contents of potash of some of the high Ce/La glasses support this hypothesis of a mineral flux.

Yatsuk (Yatsuk et al., 2024a) hypothesised that this particular group of glass may originate from Italy as this type of glass was not found outside the Italian peninsula. The data obtained from the Tsaishi assemblage shed a different light on the potential origin of these glasses. Whereas soils concretions with cerium contents exceeding 50–100 times its content in the fine earth were indeed identified in Sicily (Vodyanitskii, 2012), cerium positive anomalies were also detected in Anatolia in alkaline waters from Lake Van (Ce/La 8 to 13, Turkey, Möller and Bau, 1993).

Although it is not possible at this stage to identify the origin of this particular type of glass, the almost systematic presence of antimony, in the composition of natural tint and colourless glasses (Fig. 12), observed on both Italian and Georgian glass beads, would probably point more towards an Eastern Mediterranean origin for this type of production.

<figure><img src="image_15.png" /><figcaption>**Fig. 12.** Distribution of the studied glasses according to their manganese and antimony oxides contents.</figcaption></figure>

## 4.2. Colouring agents

Combining visual aspects and chemical compositions, the colours of the studied glass can be grouped into six main categories: natural tint/ colourless, natural tint/deeply coloured, purple, amber, black-appearing and blue/green/turquoise (Table 1). With the exception of natural tint/ colourless and purple which are only present in the high Ce/La group, the four other tints occur in the four main chemical groups. As noted above, it is not possible to identify the colouring or opacifying agents by chemical analysis alone, but using published studies on glass colouring mechanisms (Biron and Chopinet, 2013, Calas et al., 2021) it is possible to propose hypotheses on the nature of colourants and/or opacifiers present in glass.

### 4.2.1. Natural tint glass

Natural tint glass, as defined here, includes all glass for which no colouring agent can be unambiguously identified by elemental analysis. A distinction is made between colourless glass that has probably been discoloured and deeply coloured glass that has not been discoloured.

#### 4.2.1.1. Natural tint/colourless.
As notice above all the colourless glasses belong to the high Ce/La group. These beads have all a globular/ annular shape but present more variable tints and compositions. They are mainly characterised by their antimony and manganese contents (MnO 0.022 to 0.54 %; Sb₂O₃ 0.005 to 1.22 %; Fig. 12) which do not appear to be strongly correlated with the glass tints. For example, beads 4146d (MnO 0.33 %; Sb₂O₃ 0.005 %) and 569.3.c (MnO 0.022 %; Sb₂O₃ 0.28 %), are both slightly bluish, while beads 569.3.a (MnO 0.54 %; Sb₂O₃ 0.17 %) and 563.3.e (MnO 0.031 %; Sb₂O₃ 0.47 %) look more colourless. Only UV-visible-NearIR spectroscopy measurements would help to understand the colouring process of these glasses.

#### 4.2.1.2. Natural tint/deeply coloured glass.
The dark brown-green colouration of these four small annular beads is probably due both to the presence of more elevated iron oxide contents relative to those observed in colourless and amber glasses (Fe₂O₃ 0.53 to 1.9 % compared to 0.42 to 0.64 for colourless glass and 0.13 to 0.60 % for amber glass) and to the absence of antimony and manganese oxides (Fig. 12). This tint is present in the high Ce/La (1) and high Mg K (3) groups. Two of the three beads from the high Mg K groups which are representative of the classical “Mesopotamian plant ash glasses” have low alumina (Al₂O₃ ≈ 1 %) and iron (Fe₂O₃ 0.53 and 0.74 %) contents, while the third one, which is a typical high Mg K P plant ash glass, exhibits the highest alumina (Al₂O₃ 4.9 %) and iron oxide (Fe₂O₃ 1.9 %) contents of the four deeply coloured glasses.

It is also noteworthy that the two Mesopotamian plant ash glasses and the high Ce/La glass show a striking similarity in their oxide compositions. The main differences include their calcium/strontium ratios (Table S1), highlighting their different origins.

### 4.2.2. Purple glass

Purple glasses are all coloured by manganese oxides (MnO 0.88 to 1.09 %) and belong all to the high Ce/La group. Among them we find 1 bird shaped bead, 1 bi-conical bead and 4 globular/annular beads.

The Tsaishi bird shaped purple glass bead (570.1) is of particular interest as it belongs to the group of glasses with a high Ce/La ratio. The only other bead of this type for which we have complete analytical data is the one found at Capua (Ca15I) which is also a high Ce glass (Conte, 2015a, p. 102). Unfortunately, no LA-ICP-MS data are available for the 2 bird shape beads (PG172 & VG88) from Gabii/Rome and Falerii which were only analysed by pXRF (Yatsuk et al., 2024a). Another bird shaped bead, from Ras Shamra-Ugarit was analysed by PIXE (Syria, Biron et al., 2012). This bead, dated to the end of the late Bronze Age, is described as a Mycenaean import made from dark blue Egyptian glass but its composition was not published. However, the authors report that, like
those from Tsaishi and Capua, the bird-shaped bead from Syria and Italy (Gabii/Rome and Falerii) were also made from high Mg K glass. The results obtained on the bird-shaped beads from Tsaishi and Capua, which point to a common origin, highlight the importance of carrying out LA-ICP-MS analyses on a larger corpus (with a variety of origins, dates and shades) of this type of bead.

### 4.2.3. Amber glass

The colour of four small annular amber-coloured beads is probably due to the presence of the ferri-sulphide complex, Fe³⁺-S²⁻ (Paynter and Jackson, 2018). This tint is found in the high Li B (1), high Ce/La (1) and low Mg K (2) groups. While the two low Mg K amber glass are made with pure raw materials (quartz and mineral soda) and have almost identical compositions, the two others contain much higher levels of minor oxides and impurities (Table S3): the high Li B glass is also characterised by unusual high levels of arsenic (AS₂O₃ 0.27 %) and antimony (Sb₂O₃ 0.55 %) oxides.

### 4.2.4. Black-appearing glass

As shown by several authors, the colouration of black-appearing glass are difficult to characterize and may be explained by the presence of different chromophore in a wide range of concentrations (Van der Linden et al., 2009; Conte et al., 2018; Lonćarić et al., 2024, Yatsuk et al., 2024b). In our corpus, the colour of black-appearing glasses is due to the presence of high iron contents (Fe₂O₃ 12.3 to 15.3 %), three of them belong to the high Li B glass group and the last one to the low Mg K group. With the exception of a few blue/green/turquoise glasses in the 'high Li B' group (CaO 2.7 to 4.2 %), black-appearing glasses have the lowest lime contents (CaO 0.46 to 3.7 %) in our assemblage.

The three black-appearing glass of the high Li B group exhibit the lowest lithium and boron contents of this group (Fig. 4). Compositions and typologies similar to glass bead 4145a, were reported by Conte for some glass beads from Cuma (CM 3b, 2 g, 19bl, Conte, 2015a, Conte et al., 2018). Such comparison with Yatsuk et al. data (2024b) is more difficult as boron and lithium were not analysed.

From a chemical point of view, the low Mg K black-appearing glass bead has also some pendants in Italy (Conte et al., 2018; Yatsuk et al., 2024b) where some black-appearing glasses exhibit also low alumina and lime contents but, when chlorine was analysed, its content is usually higher.

### 4.2.5. Blue/green/turquoise glass

This category incorporates all glass containing copper oxide (CuO > 0.6 %), regardless of their actual colour. They are distributed across three chemical groups: three in the high Li B glass group, two in the high Ce/La group and seven in the high Mg K group (six in the high Mg K P sub-groups and one in the Mesopotamian plant ash glass sub-group). These beads are characterised by the use of a highly pure copper colourant (Cu/(Cu + Zn + Sn + Sb + Pb) > 95 %). The six blue/green/turquoise from the high Mg K P sub-group exhibiting the highest impurities contents (Table S3).

Blue/green/turquoise high Ce/La glasses were also found in Italy at Sarno and Francavilla Marittima (Conte, 2015 a; Conte et al., 2016 & 2019). Similarly, high Li B blue/green/turquoise glasses were identified at Brili (Georgia) and Hasanlu (Iran), while high Mg K glasses (high Mg K P sub-group) were found at Brili (Georgia) and Hatt (India). A comparison with the blue/green/turquoise glasses studied by Yatsuk et al. (2023) is more challenging, as the values for Li, B and P were not provided.

## 5. Discussion

The analytical results obtained on the glass beads from the Tsaishi necropolis, dating from the 8th to 7th centuries, demonstrate once more the diversity of trade routes utilised for the exchange of beads in the Caucasus. They also illustrate the variety of raw glass production

techniques employed in the Near East during the initial half of the 1st millennium BC. The evidence indicates a more intricate scenario than that previously proposed for the Georgian necropolises of Brili and Pichvnari (Vachadze et al.; Shortland and Schroeder, 2009).

The Tsaishi samples show five main categories of glass (high Li B, high Ce/La, low Mg K, high Mg K divided in “Mesopotamian type” and “high Mg K P with MgO/K₂O < 1” type). Some of these, including the high lithium and boron glass and Mesopotamian plant ash glass, have been previously documented at numerous Early Iron Age sites. Others, such as the high Ce/La glass and the high Mg K P glass have only recently been identified in some studies of Early Iron Age glass.

Regarding the high Li B group, our results point out the great diversity of compositions observed in that group, in terms of boron, lithium and some other minor oxides content highlighting probably the variability of lithium and boron contents in the mineral deposit used as soda flux. However, the compositional variability observed at Brili for most of the other minor oxides is not present at Tsaishi. In terms of their composition, Tsaishi high Li B glasses, dated from at least the beginning of the 8th century BCE, exhibit greater similarity to earlier high Li B glasses as observed in finds from Denmark and France dating from the Late Bronze Age (Varberg et al., 2015; Plouin et al., 2012; Cherel and Gratuze, 2018) than to later Brilli high Li B glasses dating from the 7th-5th centuries BC (Vachadze et al.).

The results confirm the presence of a new group of glasses with high Mg K P contents as early as the beginning of the 8th century BCE. These glasses were identified at Brili (Vachadze et al.), at Marlik and Amlash (Iran) and Hatt (India) (Lankton, forthcoming, unpublished data), and have not been identified at Iron Age sites outside the Caucasus and Mesopotamia to date.

This newly obtained data on the glass bead assemblages from the Tsaishi Necropolis reveals, for the first time in the Caucasus, the presence of a glass group exhibiting a positive cerium anomaly. This finding is significant as it challenges the previously held assumption that such anomalies were exclusive to southern and southeastern European glass assemblages of the 9th-8th centuries BC from Italy (Conte, 2015b, Yatsuk et al., 2024a) and of the Early Iron Age from Croatia (Franjić, 2019). This group comprises two bird-shaped beads: one originating from Tsaishi and the other from Cuma in Italy (Conte, 2015). Further analysis will be needed to confirm or refute the relationship between this group of glass and these beads. The provenance of this glass group remains uncertain at this time; however, a number of indicators suggest an Eastern, or potentially Caucasian or Mesopotamian, origin. Based on the chronology of the sites under consideration, this newly identified group of glass appears to represent a relatively brief production phase in the early first millennium BC. The results of this study suggest that this specific glass production centre likely had established trade routes, both to the east, in the direction of Georgia, and to the west, in the direction of Italy.

Finally, the presence of a small group of glasses (3 beads), made with a relatively pure source of silica (quartz) fused with a mineral soda flux, should be confirmed by new analyses. These glasses seem to be distinguished from Egyptian and Syro-palestinian classical natron glasses by their lower chlorine and trace elements contents. However, due to the small amount of data available for this period, it is difficult to determine whether these glasses derive from early Egyptian or Syro-Palestinian production workshops or from other glass production centres.

Studying the entire glass collections of Tsaishi's N1 and N2 burial pits creates following image: the total number of opaque and translucent glass beads, pendants, and fragments of different colours and shapes is roughly 650 units in earlier N2 pit and 900 in the later N1 pit.

The most prevalent group among analysed glasses showing the high cerium/lanthanum ratios has been recorded in both burial pits. The second pit's discoveries slightly outnumber those from the first. This group comprises of a single piece of a bird shaped bead, and other basic geometric shapes, such as conical, spherical and annular beads.

Glass groups with low magnesia, potash and phosphorus contents or
High Mg K contents are characterised by simple geometric shapes made of translucent and opaque glass. The single stylised specimens are cylindrical bead with tapered ends and a melon bead. These groups also have been evidenced in both burial pits. These glass groups from Tsaishi find stylistic parallels locally.

A considerable novelty in shapes is provided in group of glasses with high lithium and boron content. These are anthropomorphic grotesque beads, a sole large polychrome eye bead, a single piece of a zoomorphic figure (fish?), a melon and segmented beads. All mentioned shapes are in minority among Tsaishi glass findings. Furthermore, the anthropomorphic forms and large eye beads are absent in burial pit N1. All high lithium and boron glasses were identified solely in the second burial pit and therefore are the chronologically earliest group in Tsaishi necropolis.

Stylistic examinations of the entire archaeological assemblage discovered in Tsaishi Necropolis do indicate to some links with the western routes. A few anthropomorphic and zoomorphic bronze figures from burial pits N1 and N2 burial are evidence of these connections. Namely female riders on a horse having direct analogues in Samos, Greece, (Schweitzer, 1967; Jantzen, 1972; Voyatzis, 1990; Lortkipanidze, 2002; Papuashvili, 2010; Papuashvili et al., 2015; Vachadze, 2019).

Another tie can be seen in bronze vessels. Together with the bronze bells analogues of these situlas were discovered in fragments at three archaeological sites located in Sicily. The oldest discovery dates back to the early 6th century BCE. It is believed that these Colchian and/or typically Caucasian components appeared in Italy through Ionian intermedial centres (Baitinger, 2016; Vachadze, 2020;).

Conversely, the Iron Age contacts between Colchis and the far East have not been thoroughly studied and remain open. In this regard, the compositional similarity with the glasses discovered in Marlik, Amlash and Hatt appears to be one of the first factual signs of some interactions during the Iron age.

These new results obtained on Tsaishi glass beads highlight the diversity of production encountered in the Caucasus at the beginning of the first half of the 1st millennium BC. Alongside plant ash Meso-potamian glasses and high Li B glasses which lasted practically until the end of the first millennium AD it seems that we are dealing with multiple small productions that vary greatly in composition. This is the case, for example, with the plant ash glasses referred to as high Mg K P, that have only been identified in the Caucasus and Mesopotamia, and with the positive cerium anomaly glass group.

## 6. Conclusion

The examination of 38 samples from Tsaishi dated with the 8th-7th centuries BC has shown the following picture: Tsaishi glasses fall into five main groups (high Li B, high Ce/La, low Mg K, high Mg K divided in “Mesopotamian type” and “high Mg K P with MgO/K2O < 1” type). Their colour spectrum is represented with: amber, blue/green/turquoise, colourless purple and black appearing shades.

Tsaishi findings indicate to a presence of High Mg K and high lithium boron glass groups as early as the beginning of the 8th century BCE. These two groups have already been identified in Colchis' northern mountainous area at Brili and the high lithium boron group was found to its South, on the eastern black sea coast at Pichvnari necropolis.

From the chemical and typological points of view group with high cerium/lanthanum ratios has direct resemblance to the coeval glass beads found in different archaeological sites of Italy and Croatia. For the first time the area of glasses with a positive cerium anomaly is expanded to include the Caucasus, namely central Colchis. The existence of a small group of glass with low Mg K is another novelty that has to be confirmed by new analyses.

In Colchis, glass seems to have been a popular material since the beginning of the 1st millennium BC. This is reflected in the variety of Tsaishi glasses that can be found both in the big or small-scale markets of

the eastern and western regions. Certain glass products would have been imported into Colchis as ingots, others as completed goods. These interactions may have occurred directly or through intermediary centres. For the first time, a factual foundation for these early contacts during the 8th and 7th centuries BC has been demonstrated. This study also suggests the possibility of small-scale production of some glass groups in the Caucasus. Further analyses of glasses from other Colchian burial pits will add important novelty to these issues.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgement

For cooperation, special thanks to the administration and stuff of the Dadiani Palace History and Architectural Museum.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jasrep.2025.105066.

## Data availability

I have put all the data used in that paper as supplementary material

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