Evidence for glass ‘recycling’ using Pb and Sr isotopic ratios and Sr-mixing lines: the case of early Byzantine Sagalassos

The secondary production (working) of glass from imperial to early Byzantine times has been proven at the ancient city of Sagalassos (SW Turkey) by the existence of glass chunks, fuel ash slag and kiln fragments related to glass processing. It had been previously suggested that local green glass might have been recycled from two other locally found glass types (blue glass vessels and chunks and HIMT glass chunks). This paper provides analytical evidence for the recycling of glass next to the use of imported raw glass. The heterogeneous lead isotopic composition of the green and HIMT vessel glass at Sagalassos, with as end members on the one hand the isotopic composition of local blue glass vessels and chunks and on the other hand that of the HIMT glass chunks, could indicate the production of ‘recycled’ glass, although heterogeneous raw materials could have been used. However, the use of Sr-mixing lines confirms local recycling. It is clear that the Sr in the green and HIMT vessels is a mixture of the Sr in the aforementioned end members. It cannot be proved whether the green ‘recycled’ glass was produced from a mixture of chunks alone, or from a mixture of cullet and chunks. Suggestions are made towards the possible origin of the raw materials for the blue and HIMT glass on the basis of Sr isotopic signatures and absolute Sr contents in the glass.     

The Production and Circulation of Carthaginian Glass Under the Rule of the Romans and the Vandals (Fourth to Sixth Century ad): A Chemical Investigation

Fifty‐seven glass samples from Carthage dating to the fourth to sixth century ad were analysed using the electron microprobe. The results show that these samples are all soda–lime–silica glass. Their MgO and K₂O values, which are below 1.5%, suggest that they were made from natron, a flux that was widely used during the Roman period. The major and minor elements show that these samples can be divided into four groups, three of which correspond to the late Roman period glass groups that were found throughout the Roman Empire: Levantine I, and ‘weak’ and ‘strong’ HIMT. Of particular interest is our Group 2, which is technologically and compositionally similar to HIMT glass and the CaO and Al₂O₃ values of which are similar to those of Levantine I. Glass of similar composition has been reported by several authors and is predominantly found dating from the late fifth to seventh century. This could represent a ‘new’ glass group; therefore further study is needed to determine its origin. Also, this study suggests that the Vandal invasion in North Africa did not disrupt the glass trade between Carthage and the Levantine coast.     

The composition of late Romano-British colourless vessel glass: glass production and consumption

One hundred and twenty-eight colourless glass tablewares from settlement contexts throughout the British Isles, dating from the mid-3rd to 4th century AD, were analysed by ICP-AES spectrometry. Three distinct compositional groups were identified based upon the use of different decolourisers and primary raw materials, with possible sub-groups within these. These compositions have distinct, but overlapping chronological ranges, suggesting colourless glass production in at least three, possibly more, centres in the late Roman period. The compositional analysis highlights the high degree to which recycling of glass was taking place during this late period. The chronological distribution of some of these compositions is more restricted within the British assemblages than is observed in other published assemblages from Western Europe. This distinction may indicate different supply patterns of glass to the Western provinces.     

The coloured glass of Iulia Felix

Research on the cargo of glass in the Roman ship Iulia Felix, wrecked off the town of Grado (province of Udine, North Italy) in the first half of the 3rd century AD and composed of recycling cullet carefully selected for colour and type, provided much information on Roman glass production technology. A combined approach, involving analytical, statistical, and archaeological evidence, included chemical analyses (X-ray fluorescence, electron microprobe), which indicated that the coloured samples were all soda-lime-silica in composition, with natron as flux, although cluster analysis identified many compositional groups. Comparisons among the compositional groups of the colourless glass, previously studied, and those of coloured glass showed that the production technologies of the colourless glass vessels constitute two well-defined technological end-members, also related to group types, into which those of the coloured glass samples fall. In particular, coloured glass samples—all bottles, low-status vessels—were produced with mainly beach siliceous-feldspar-calcareous sand. However, unlike the colourless type, strict control of raw materials and decolourising processes was not adopted, and recycling was also practised, as demonstrated by the Sb₂O₃, Cu and Pb patterns. In this context, a “recycling index” (RI)—[(Sb₂O₃)_X/(Sb₂O₃)_Ref] * 100—is proposed here for the first time, in order to quantify the extent of recycling of antimony colourless glass in the batch. RI is valid for glass containing abundant Sb from an end-member of colourless glass. In conclusion, although it cannot be stated unequivocally that the identified compositional trends are related to different production centres or different raw materials, the strong evidence of compositional variability among all the Iulia Felix glass samples, both colourless and coloured, supports the dispersed production model for Roman glassware and the common practice of recycling in Roman imperial times, especially for low-status vessels.     

Late antique glass from Salapia: Tracking production and trading networks

The investigation of 38 late antique vessels from the archaeological excavation of Salapia has been performed using EMPA and LA-ICP-MS. The collection was made using impure sands and mineral soda. Among coloured glass, most vessels were made of ‘fresh’ glass. The use of colouring agents is rare, and most decoloured glass is obtained by Mn addition. Sb-decolouration is limited to one cup, and two colourless vessels show both manganese and antimony. As for provenance, the prevalence of Egyptian-HIMT glass over the Levantine is evident. Among Levantine glass, Jalame glass is represented, whereas Apollonia glass is absent. Among Egyptian (and deemed Egyptian) glass, the prevalence of HIMT glass over the other types has been observed. The high attestation of fresh glass, most notable in the earlier centuries, suggests the importation of glass in the form of finished objects, especially luxury vessels.     

Radical changes in Islamic glass technology: evidence for conservatism and experimentation with new glass recipes from early and middle Islamic Raqqa,Syria*

The chemical analysis of excavated glass fragments from dated archaeological contexts in Raqqa, Syria, has provided a detailed picture of the chemical compositions of artefacts deriving from eighth to ninth and 11th century glassmaking and glassworking activities. Evidence for primary glass production has been found at three excavated sites, of eighth to ninth, 11th and 12th century dates; the first two are discussed here. The 2 km long industrial complex at al‐Raqqa was associated with an urban landscape consisting of two Islamic cities (al‐Raqqa and al‐Rafika) and a series of palace complexes. The glass fused and worked there was presumably for local as well as for regional consumption. Al‐Raqqa currently appears to have produced the earliest well‐dated production on record in the Middle East of an Islamic high‐magnesia glass based on an alkaline plant ash flux and quartz. An eighth to ninth century late ‘Roman’/Byzantine soda–lime recipe of natron and sand begins to be replaced in the eighth to ninth century by a plant ash – quartz Islamic soda–lime composition. By the 11th century, this process was nearly complete. The early Islamic natron glass compositional group from al‐Raqqa shows very little spread in values, indicating a repeatedly well‐controlled process with the use of chemically homogeneous raw materials. A compositionally more diffuse range of eighth to ninth century plant ash glass compositions have been identified. One is not only distinct from established groups of plant ash and natron glasses, but is believed to be the result of experimentation with new raw material combinations. Compositional analysis of primary production waste including furnace glass (raw glass adhering to furnace brick) shows that contemporary glasses of three distinct plant ash types based on various combinations of plant ash, quartz and sand were being made in al‐Raqqa during the late eighth to ninth centuries. This is a uniquely wide compositional range from an ancient glass production site, offering new insights into the complexity of Islamic glass technology at a time of change and innovation.     

The colourless glass of Iulia Felix

The present paper focuses on 85 colourless glass samples selected among the recycling cullet found in the Roman ship Iulia Felix, wrecked off the town of Grado (province of Udine, North Italy) in the first half of the 3rd century AD, with the aim of examining their chemical composition, investigating similarities within and between the three established group types (cups, plates, bottles), and comparing the chemical compositions of the Iulia Felix glass samples with groups reported in the literature for colourless glasses. Chemical analyses, performed by X-ray fluorescence and electron microprobe, indicate that the samples were all soda-lime–silica in composition, with natron as flux, according to typical Roman production technologies. Chemical data are treated by multivariate statistical tools, such as cluster analysis and the NPC test. Statistical analyses allow us to conclude that the Iulia Felix colourless glasses were produced by at least two different production technologies related to group type, confirming the trend recently identified in the literature. In addition, the trace element patterns (particularly those of Sr, Zr and Ba) suggest that beach sand with differing amounts of alkali feldspars was predominantly used as raw material, like those specifically mentioned by Pliny for glass production.     

MEDIEVAL GLASS FROM ROCCA DI ASOLO (NORTHERN ITALY): AN ARCHAEOMETRIC STUDY

An archaeometric study was performed on 33 medieval glass samples from Rocca di Asolo (northern Italy), in order to study the raw materials employed in their production, identify analogies with medieval glass from the Mediterranean area and possible relationships between chemical composition and type and/or production technique, contextualize the various phases of the site and extend data on Italian medieval glass. The samples are soda–lime–silica in composition, with natron as flux for early medieval glasses and soda ash for the high and late medieval ones. Compositional groups were identified, consistent with the major compositional groups identified in the western Mediterranean during the first millennium AD . In particular, Asolo natron glass is consistent with the HIMT group and recycled Roman glass; soda ash glass was produced with the same type of flux (Levantine ash) but a different silica source (siliceous pebbles, and more or less pure sand). Cobalt was the colouring agent used to obtain blue glass; analytical data indicate that at least two different sources of Co were exploited during the late medieval period. Some data, analytical and historical, suggest a Venetian provenance for the high/late medieval glass and a relationship between type of object (beaker or bottle) and chemical composition.     

Glass from the Archaeological Museum of Adria (North-East Italy): new insights into Early Roman production technologies

In the present study, the first archaeometric data on an ample selection of intentionally coloured (or decoloured) Early Roman glass (1st–2nd centuries AD) from the Archaeological Museum of Adria (Rovigo, Italy) are reported. The analysed samples are 61 in total, both transparent and opaque, and were characterised from the textural (SEM-EDS), mineralogical (XRPD) and chemical (XRF, EPMA, LA-ICP-MS) points of view. This combined approach allowed us to identify the raw materials and production technologies employed in the manufacture of glassware. Results for the transparent samples show that they are all silica-soda-lime glasses. Most of them, independently of colour, have compositions close to those of typical Roman glass, produced with natron as flux. No relationships were identified among chemical compositions, types or production techniques, but a dependence on bulk composition was identified for some particular colours, revealing the careful and intentional selection of raw materials. This is the case of Sb-colourless glass, produced with sand of high purity, a group of intensely coloured objects, mainly emerald green and black, produced with soda ash as flux, and some blue examples produced with various sources of sand or soda ash as flux. Two main types of opacifiers were identified for the opaque samples: calcium antimonate for white, mauve and blue glasses, and lead antimonate for the yellow ones; in one case, a yellow lead-tin antimonate was also identified. As regards the opaque glasses, most of the samples opacified with calcium antimonate are silica-soda-lime in composition, similar to the typical Roman glass. Instead, samples opacified with lead and/or lead-tin antimonates are lead glasses, suggesting different production technologies.     

Chemical characterisation and manufacturing technology of late Roman to early Byzantine glass from Beit Ras/Capitolias,Northern Jordan

The finding of considerable collections of glass artefacts, together with considerable lumps of glass chunks, fuel ash slag and kiln fragments related to glass processing strongly suggests a local secondary production (working) of glass at the Beit Ras/Capitolias archaeological site in northern Jordan from the late Roman to the early Byzantine period. The chemical analysis of ancient glasses can provide important information regarding the manufacturing technology of the glass made during a specific period. The aim of this study is to characterise the chemical and technological aspects of late Roman to early Byzantine glasses excavated from this main archaeological site. Furthermore, the present paper aims to provide incontrovertible evidence that this site must be considered as a major centre for the secondary production of glass during a period between the 3rd and the 6th centuries. For this purpose, a considerable group of raw glass chunks and vessel fragments of different colours and typologies were collected. The results of chemical analyses indicated that the glass did not show a clear difference in chemical composition between late Roman and early Byzantine times. All the glasses (artefacts and chunks) are of the soda-lime-silica type and correspond to the previously defined Levantine I glass group. The chemical composition of the glass chunks, identical to that of contemporary glass of the same colour, strongly suggests that these chunks were used for the manufacture of late Roman to early Byzantine glass at Beit Ras. The observation of technological features indicates that glass chunks were produced in massive tank furnaces in other primary production centres elsewhere, and were meant for local reworking. According to the microscopic examination, it can also be observed that mould-blowing was the main technique used for forming glass.     

Pliny the Elder and Sr–Nd isotopes: tracing the provenance of raw materials for Roman glass production

In Roman and Byzantine times, natron glass was traded throughout the known world in the form of chunks. Production centers of such raw glass, active from the 4th to 8th century AD, were identified in Egypt and Syro-Palestine. However, early Roman primary glass units remain unknown from excavation or scientific analysis. The ancient author Pliny described in 70 AD that besides Egyptian and Levantine resources, also raw materials from Italy and the Gallic and Spanish provinces were used in glass making. In this study, the primary provenance of 1st–3rd century AD natron vessel glass is investigated. The use of combined Sr and Nd isotopic analysis allows the distinguishing and characterizing of different sand raw materials used for primary glass production. The isotope data obtained from the glass samples are compared to the signatures of primary glass from known production centers in the eastern Mediterranean and a number of sand samples from the regions described by Pliny the Elder as possible sources of primary glass. Eastern Mediterranean primary glass has a Nile dominated Mediterranean Nd signature (higher than −6.0 ? Nd), while glass with a primary production location in the western Mediterranean or north-western Europe should have a different Nd signature (lower than −7.0 ? Nd). Most Roman glass has a homogeneous ⁸⁷Sr/⁸⁶Sr signature close to the modern sea water composition, likely caused by the (intentional) use of shell as glass raw material. In this way, strontium and neodymium isotopes now prove that Pliny's writings were correct: primary glass production was not exclusive to the Levant or Egypt in early Roman days, and factories of raw glass in the Western Roman Empire will have been at play.     

Glass and glass production in the Oman peninsula in antiquity reconsidered – chemical and mineralogical investigation of sands

A batch of green‐ and amber‐coloured glass chunks and unguentaria dating from the first century CE was found in 2007 at Dibba al Hisn, a site on the Arabian Sea coast of the United Arab Emirates (UAE). Its elemental and isotopic composition revealed the glass to be of a previously unknown plant ash glass type, different from known contemporary Roman, Mesopotamian, and Indian glass. The Sr isotopic composition of the glass corresponds to locally available plants, pointing to the possible existence of a first‐century CE local glass production centre. To explore this possibility, sands from around the UAE were analysed to establish their suitability for glass making and correspondence with the Dibba finds. This paper presents the results of the elemental analysis of fourteen sands. The analysis, performed using inductively coupled plasma optical emission spectroscopy (ICP‐OES), revealed all sands to be rich in lime and alumina. X‐ray diffraction revealed the presence of calcite and other carbonate minerals, as well as antigorite and quartz. Comparison of the sand compositions to average first‐century CE non‐Roman glass found at Dibba showed them to be unsuitable as raw material for producing the glass of Dibba. The evidence thus identifies this glass batch as imported, contrary to what was suggested before. This paper also reviews the occurrence of thick‐walled unguentaria in the region.     

WASTE GLASS,VESSELS AND WINDOW‐PANES FROM THAMUSIDA (MOROCCO): GROUPING NATRON‐BASED BLUE–GREEN AND COLOURLESS ROMAN GLASSES

A collection of window‐panes, vessels and alleged waste from Thamusida has been investigated by OM, SEM–EDS, ICP–MS, ICP–OES and XAS at the Fe–K and Mn–K edges. Glass samples have been characterized as natron‐based soda–lime–silica glasses, with low magnesium and low potassium. The results have been compared with 43 reference groups available for ‘naturally coloured’ and colourless glasses of both Roman and later ages. Two main types were distinguished: RBGY 1 (R oman B lue–G reen and Y ellow 1) and RBGY 2 (R oman B lue–G reen and Y ellow 2). Given their compositional similarity to the Levantine I or, to a lesser extent, HIMT glasses, the Syrian–Palestinian coast for RBGY 2 and Egypt for the RBGY 1 have been suggested for their provenance. Most Thamusida samples have been assigned to the RBGY 2 type. A small group of Thamusida colourless vessels was included into the RC (R oman‐C olourless) compositional field; the latter still being defined. The alleged waste pieces may define a local production that should have been of secondary type. The investigations performed on local raw materials seem to discount the possibility of a primary glass‐making site. XAS measurements determined that Fe²⁺ contents ranging between 30 and 52% are able to assure an aqua blue colour; below 30%, the glasses turn light green or light yellow.     

A cost surface model of volcanic glass quarrying and exchange in Hawai‘i

The spatial distribution of artifacts from the Pu‘u Wa‘awa‘a volcanic glass source (North Kona District, Hawai‘i Island) shows a pattern of direct access by those living in the immediately vicinity of the source with subsequent down-the-line exchange. Most quarrying and exchanges likely occurred within a single day’s travel from sites where artifacts were deposited. The exception to this is the discovery of non-local direct access evident in assemblages from the extreme southern end of Hawai‘i Island; these visits may have involved voyages by canoe. While people did not often travel far for volcanic glass they nonetheless appear to have had unfettered accessed to source material and freely conducted inter-community exchanges. This implies volcanic glass was treated as a common pooled resource and the existence of informal exchange relationships.     

ANALYSIS OF LATE BRONZE AGE GLASS AXES FROM NIPPUR—A NEW COBALT COLOURANT

A multidisciplinary study of a unique group of Late Bronze Age (LBA) ceremonial glass axe heads and other artefacts shows that these are the first significant group of glasses coloured with cobalt to be identified from the Near East. The axes were excavated from the site of Nippur, in present‐day Iraq. Several are incised with the names of three kings, which dates the material to the 14th–13th centuries bc . Analysis by laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) indicates that the glass had high magnesia (MgO) and potash (K₂O) associated with a plant‐ash flux and was coloured blue by copper or a combination of copper and cobalt. These glasses are similar, but not identical, in major element composition to blue‐coloured glasses manufactured in ancient Egypt and elsewhere in Mesopotamia in the same period. However, the Nippur cobalt‐ and copper‐coloured glasses exhibit significantly different trace elemental compositions compared to Egyptian glass coloured with cobalt, showing that the ancient Near Eastern glassmakers had clearly identified and utilized a distinctive cobalt ore source for the colouring of this glass. Since it was previously thought that the only cobalt ores exploited in the LBA were exclusively of Egyptian origin, this new finding provides new insights on the origins of glass and how it was traded during the Bronze Age period.     

Electron Microprobe Analysis of 9th–12th Century Islamic Glass from Córdoba,Spain

Twenty‐six samples from domestic assemblages of 9th–12th century Córdoba were subjected to electron microprobe analysis. The results reveal two main compositional types. The first, encountered in 13 of the samples, seems to result from the combination of plant ashes with high‐impurity sand, and has some contemporary parallels from Syria and Egypt. The second type is a lead–soda–silica glass, encountered in a relatively high proportion of the glasses (11 of the 26 sampled), possibly formed by the addition of lead metal to existing glasses and with very few known parallels. These are among a very small number of results available to date on the chemical composition of glasses from medieval Spain, and the presence of a high proportion of lead–soda–silica glasses is particularly interesting, possibly indicating a technological practice unique to, or originating in, the western Muslim world.     

THE COMPOSITION AND MANUFACTURE OF EARLY MEDIEVAL COLOURED WINDOW GLASS FROM SION (VALAIS,SWITZERLAND)—A ROMAN GLASS‐MAKING TRADITION OR INNOVATIVE CRAFTSMANSHIP?*

Archaeological excavations between 1984 and 2001 at the early Christian cemetery church in Sion, Sous‐le‐Scex (Rhône Valley, Switzerland), brought to light more than 400 pieces of coloured window glass dating from the fifth or sixth centuries ad . The aims of this paper are threefold: first, to characterize the shape, colour and chemical composition of the glass; secondly, to understand whether the production of the coloured window panes followed traditional Roman glazing techniques or was of a more innovative nature; and, thirdly, to provide some indications as to the overall design of these early ornamental glass windows. Forty samples of coloured glass have been analysed by wavelength‐dispersive X‐ray fluorescence. The results of the chemical and the technological studies showed that most of the glass was produced using recycled glass, particularly as a colouring agent. Some of the glass was made of essentially unmodified glass of the Levantine I type. The results taken together seem to confirm that raw glass from this region was widely traded and used between the fourth and seventh centuries ad . The artisans at Sion were apparently still making use of the highly developed techniques of Roman glass production. The colour spectrum, manufacture and design of the windows, however, suggest that they represent early examples of ornamental coloured glass windows.     

MAKING COLOURLESS GLASS IN THE ROMAN PERIOD*

This paper discusses the compositional analysis of Roman colourless glass from three sites in Britain. The findings suggest that two broad compositional groups can be identified on the basis of the choice of the initial raw materials selected for glass production, in particular the sand. The largest of these groups is inherently different from the naturally coloured, blue–green glasses of the same period, while the other group is compositionally similar. Further subgroups are apparent on the basis of the decolorizers used. These glass groups are explored in the light of the current theories concerning the organization of glass production in the Roman world.     

Rationales in Old World Base Glass Compositions

It is long known that most Egyptian and Roman base glass compositions show a remarkably small scatter in their chemical composition. By plotting appropriately reduced base glass compositions in ternary phase diagrams it is demonstrated that the compositional fields defined by the compositional scatter are closely related to eutectic regions within the relevant phase diagrams. This is interpreted as to be due to an eutectic melting regime, i.e. partial melting in the presence of a crystalline buffer or residuum, and not primarily a result of strict recipe and raw material control. Furthermore, it is demonstrated that possibly two independent melting temperature indicators are correlated, suggesting a factual relationship between melting temperature and melt composition. This evidence is taken to develop a “partial batch melting model” for these early glasses, as opposed to the “total batch melting model” of Mediaeval and early modern glasses. Some archaeological implications of this model are briefly discussed.     

The Supply of Glass at Portus Ilicitanus (Alicante,Spain): A Meta‐Analysis of HIMT Glasses

Portus Ilicitanus (Picola, Alicante) was the main sea harbour of the Roman Colonia Iulia Ilici Augusta and as such played a crucial role in the supply of fundamental commodities to the Iberian Peninsula. Excavations yielded large quantities of glass in fourth‐ and early fifth‐century contexts. Elemental analysis of 60 samples by laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) confirmed that the glasses were imported from the Eastern Mediterranean. A majority of the glasses correspond to the HIMTa primary production group, which originates from Egypt. The statistical evaluation of published data of 589 HIMT glasses further revealed differential distribution patterns of the HIMTa and HIMTb subtypes between the Eastern and Western Mediterranean, suggesting chronological trends that are linked to wider geopolitical changes. This demonstrates the need for systematic large‐scale approaches to identify supply patterns and possible factors underlying geographical differences and/or chronological developments.