MEDIEVAL LEAD GLASS IN CENTRAL EUROPE

In Trommsdorfstraße, Erfurt, a glass‐processing workshop has been excavated, which produced lead glass rings and beads in the 13th century. This workshop produced two different lead glasses. The first, a high‐lead glass, could be found throughout Europe, from England to Russia. However, another newly defined type of glass could be identified (Central European lead–ash glass). This can be demonstrated by analysing the literature, and it has been found in eastern Germany, Poland, Slovakia and the Czech Republic. A Slavic lead–ash glass with the same ash content as the Central European lead–ash glass but lower amounts of lead was produced in Eastern Europe. In western Germany, another type of ash (beech ash) was used to produce a wood‐ash lead glass. Lead‐isotope analysis proved that the same source of lead was used for the wood‐ash lead glass and the high‐lead glass in western Germany and the two types of glass from Erfurt.     

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.     

δ18O measurements of archaeological glass (Roman to Modern age) and raw materials: possible interpretation

The present paper reports results from a systematic study of oxygen isotopic compositions for glass samples from various archaeological sites (i.e., Iulia Felix, Grado, Vicenza, Pozzuoli and Modena in Italy, and Derrière Sairoche in Switzerland) and dated from the Roman period to the 18th century AD, as well as of some raw materials that may have been used for their production. The analysed samples differ essentially in the type of flux, using Roman and high Medieval glass natron and late Medieval and modern glass plant ash, soda and potash, respectively. The aim of this study was to amplify the database of oxygen isotope data for various archaeological glasses and to identify isotopic trends indicating different raw materials, production technology, and/or provenance. Results indicate that natron glass samples of various provenance and age have consistently higher δ¹⁸O values than plant ash ones (about 15.5‰ vs 13.0‰), probably due to the different flux, highly ¹⁸O-enriched in the case of natron. Isotopic data on Belus and Campanian sands, the types mentioned by Pliny for glass production, show that they have similar isotopic composition. Taking into account the oxygen isotopic composition of Roman glass, the “positive natron effect”, and the negligible influence of small amounts of manganese and antimony containing decolourisers, the suitability of both sources for glass production is verified, supporting the hypothesis of multiple sand sources. Notwithstanding this, the isotopic similarity between Belus and Campanian sands prevents us from identifying the starting material from the δ¹⁸O of the final product. In the case of plant ash used as flux, it is not possible to distinguish between soda and potash plant ash, because the addition of ash did not contribute isotopically heavy oxygen and the silica source is presumed to be comparable in the analysed samples. The isotopic data of the present study are also compared with those already published in the literature, and possible interpretations on their analogies and differences are discussed.     

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.     

New insights into Byzantine glass technology from loose mosaic tesserae from Hierapolis (Turkey): PIXE/PIGE and EPMA analyses

This study focuses on the Byzantine glass tesserae from Hierapolis (Phrygia, central Turkey). Fifty-seven samples of loose tesserae from two sites in the town (the theatre and the church of St. Philip) are analysed by particule-induced X-ray emission and particule-induced gamma ray emission and electron probe X-ray microanalysis to obtain the chemical composition and identify the colourants and opacifiers. The aims are to add new information to the scant knowledge of the Byzantine glassmaking technology, to constrain the chronology of the mosaics and to trace the supply routes of the tesserae. In the destruction layers of the theatre, tesserae produced following the Roman glassmaking technology (natron glass opacified by calcium and lead antimonate) were found. They were made using a Levantine 1 raw glass, generally attributed to the early Byzantine period (fifth to sixth c.). In the church, the samples attest a technological change from Roman tradition, and a complex pattern according to building history (two phases are attested, probably in the sixth and eighth to ninth c.), and a multiplicity of supply. Three glass types and some recipes not attested before in this chronological range for the production of tesserae are documented, such as the use of a local low-chlorine natron glass for the production of black and red tesserae, the blue colouring by a source of cobalt with zinc in a natron glass tessera and the opacification with tin oxide (both in a lead-free and in a high-lead natron glass), as well as with quartz.     

RAW MATERIALS OF GLASS FROM AMARNA AND IMPLICATIONS FOR THE ORIGINS OF EGYPTIAN GLASS*

Analysis has been conducted on 19 blue glasses from Amarna in Middle Egypt dated to around 1350 BC. The results suggest that these glasses fall into two distinct types: cobalt coloured glasses with a natron based alkali made from local Egyptian materials, and copper coloured glasses with a plant ash alkali, which follow a Mesopotamian tradition of glass making. It is suggested that at least some of this copper/plant ash glass is imported into Egypt during the Amarna period despite extensive local production of cobalt/natron glass. Existing analyses (Lilyquist and Brill 1995) of the earliest glass from the reign of Tuthmosis III (c. 1450 BC) suggest that during this period the same two types of glass are present. Local Egyptian cobalt and natron in these early glasses implies that, despite the lack of archaeological evidence for production sites, glass was produced from its raw materials in Egypt as early as the reign of Tuthmosis III.     

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.     

The glass of Nogara (Verona): a “window” on production technology of mid-Medieval times in Northern Italy

The site of Nogara (province of Verona, Italy) provides valuable insights into the complexities of the glass industry in mid-Medieval times, due to its timing, which ranges mainly between the 10th and 11th centuries AD, and to the great quantity of glass findings, mainly tableware. In the present paper, the combination of archaeological, chemical and textural data allows us to identify production technologies in a time-interval perceived to be a period of technological transition for glass. In particular, the frequent occurrence of recycled natron glass and only a few glass samples made with soda plant ash indicate that recycling of earlier glass was common in inland Northern Italy in the 10th–11th centuries AD. In addition, blue and reticello decorations were obtained by recycling earlier glass mosaic tesserae, as shown by much Co, Cu, Sn, Sb and Pb and the presence of crystallised calcium antimonates. A few glass samples with chemical compositions intermediate between natron and soda plant ash glass were also identified, suggesting a gradual change in glass composition from natron-based towards soda ash-based production technology, which prevailed in the 13th-14th centuries. In conclusion, the difficulty in describing mid-Medieval glass as a well-defined entity, due to the great propensity for recycling earlier glass samples which causes variability in chemical compositions, particularly those of trace elements, is clearly documented here. In any case, this paper contributes to a new type of chrono-typological scanning and to more detailed knowledge of glass production technology during mid-Medieval times in Northern Italy, little found in the literature until now.     

Glassmaking using natron from el-Barnugi (Egypt); Pliny and the Roman glass industry

Pliny the Elder describes the discovery of a process for making natron glass, which was widely used for much of the first millennium bc and ad. His account of glassmaking with natron has since been corroborated by analyses of archaeological glass and the discovery of large-scale glass production sites where natron glass was made and then exported. Analyses of Egyptian natron have shown it to be a complex mixture of different sodium compounds, and previous experiments to make glass with Egyptian natron have been unsuccessful. Here, natron from el-Barnugi in the Egyptian Nile delta, a site which also probably supplied Roman glassmakers, is used to produce glass. The experiments show that high-quality glass, free of unreacted batch or bubbles, could have been produced from natron in its unprocessed form in a single stage, that larger quantities of natron would be required than has previously been anticipated, that the presence of different sodium-containing compounds in the deposit aided melting, and that negligible waste is produced. The implications for the identification of glass production sites, for the organisation of trade and for the supply of natron within and outside Egypt are discussed in the light of Pliny’s accounts.     

Natron as a flux in the early vitreous materials industry: sources,beginnings and reasons for decline

Natron deposits, the best known of which being those at Wadi Natrun in Egypt, have been used as the flux in the production of vitreous materials from the early 4th millennium BC onwards. In the present paper, the history of the use of natron as a flux is traced from its beginnings in the glaze of Badarian steatite beads, through its use in glass production starting in the 1st millennium BC, until its apparent shortage during the 7th to 9th centuries AD, and its subsequent replacement by plant ash during the 9th century AD. Documentary evidence for possible natron sources in Egypt, including the Wadi Natrun, and around the eastern Mediterranean is summarised, and the results of recent fieldwork at the Wadi Natrun and at al-Barnuj in the Western Nile Delta are presented. The possible reasons for the apparent shortage of natron from 7th to 9th centuries AD and its subsequent replacement by plant ash as the flux used in glass production during the 9th century AD are then considered. These include the possibility that, because of the massive scale of glass production, the demand for natron exceeded its supply; the possible effect of climatic changes; and the potentially disruptive role of political events in the Wadi Natrun–Delta region.     

Change in chemical composition of early Islamic glass excavated in Raya,Sinai Peninsula,Egypt: on-site analyses using a portable X-ray fluorescence spectrometer

The Raya port (eighth to 12th centuries) on the Sinai Peninsula, Egypt, was one of the important port cities for the Red Sea trade. We performed on-site analyses of Islamic glass vessels (used in eighth to 11th centuries) mainly from this site in Egypt using a portable XRF spectrometer. The aim of this paper is to contribute to our understanding of the chemical compositions of early Islamic glass vessels by comparing their archaeological date and typology. In the early Islamic period, glass objects were mainly produced from natron as the soda source. Among the natron glass analyzed in this study, glass vessels with low titanium and iron and high strontium contents, which were probably produced in the Syria–Palestine region, were excavated in the eighth century layer. From the ninth century layer, a large number of samples with high levels of calcium, titanium and iron, probably produced in Egypt, were found. It should be noted that a large number of glass vessels with this chemical composition were found at the Raya site, because this type of glass was rarely reported from other Islamic sites. We finally concluded that this type of glass seems to be produced under a fixed recipe, although some samples contain a colorant or decolorized materials.     

Production Technology for Copper‐ and Cobalt‐Blue Vitreous Materials from the New Kingdom Site of Amarna—A Reappraisal*

Previously published data on the chemical compositions and microstructures of copper‐ and cobalt‐blue frit, glass and faience from the New Kingdom site of Amarna in Egypt ( Shortland 2000 ) are summarized. The data are then used to infer the raw materials and processes employed in the production of these vitreous materials. The results suggest that crushed quartz pebbles were the source of the quartz for all the materials, but that different sources of alkali, both natron and a range of plant ashes, were used in the production of each material. It seems probable that the cobalt‐rich alum colorant was pre‐treated before use by precipitating cobalt hydroxide from a solution of the alum by the addition of natron. It is further hypothesized that cobalt‐blue glass was produced by melting the cobalt‐blue frit together with additional plant ash and possibly quartz. Finally, it is suggested that, in glazing the cobalt‐blue Variant D faience first produced in the 18th Dynasty, the efflorescence or application method was selected according to object type.     

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 on the Amber Road: the chemical composition of glass beads from the Bronze Age in Poland

The article discusses the chemical composition of 56 glass samples from 52 beads found in Poland at 13 archaeological sites (mainly cemeteries). The artefacts have been dated to the II–V period of the Bronze Age (=phases BzB–HaB; c. 1600–750/700 bc). The LA-ICP-MS method was applied. Two groups were distinguished in this assemblage based on a comparison of the MgO to K₂O ratio in glass: (i) high magnesium glass (HMG)—23; and (ii) low magnesium and high potassium glass (LMHK)—33 (29 matrix glass specimens and 4 decorative). In southern Poland, beads made of HMG and LMHK are often found in the same cemeteries. Analyses have shown that HMG was most probably made in Mesopotamia and that at least one cobalt glass is of Egyptian provenance. LMHK glass was made in Europe, most probably in Italy. Also, Italy was the most probable transit point for artefacts made of HMG en route to East-Central Europe.     

Potassium–Calcium Glass: New Data and Experiments*

The chemical composition of potassium–calcium ‘wood‐ash’ glass reflects the elemental pattern of the involved non‐volatile base materials in quartz sand, wood ash and possibly potash. The essential elemental ratio K₂O/CaO of wood ash varies between 0.2 and 0.8, and depends on the habitat and geological substratum of the wood rather than on the tree species; ratios between 1.0 and 3.0 in wood‐ash glass are only possible when potash is added as a third base material. Melting temperatures of wood‐ash glass sensu stricto, termed K–Ca‐2, produced with the two raw materials quartz sand and wood ash, are between 1250°C and 1400°C, while those of three‐component‐glasses, termed K–Ca‐3, are between 900°C and 1250°C, according to the amount of added potash. Experimentally produced glass displays different hues, from colourless to brown, olive‐green and pink, according to the chemical composition of the wood ash. Elevated MnO concentrations between 0.5 and 3 wt% may originate from wood ash and are hence not necessarily an indicator of colour‐inhibiting additives. Phosphate stemming from wood ash is an essential discriminator between wood‐ash glass and potash–lime glass. Because wood ash contains only minor amounts of sodium, wood‐ash glass with equal concentrations of potassium and sodium is a hybrid glass type, where besides quartz sand, wood ash, possibly potash and also soda‐rich cullet have been applied for glass production.     

DATA ON 61 CHEMICAL ELEMENTS FOR THE CHARACTERIZATION OF THREE MAJOR GLASS COMPOSITIONS IN LATE ANTIQUITY AND THE MIDDLE AGES

Sets of 20 soda ash, 16 soda lime and 23 wood ash glasses mainly from excavations in Europe were analysed by microprobe and LA–ICP‐MS for 61 elements and are presented as average concentrations with standard deviations. Concentrations of sodium, potassium and magnesium allow the major glass type to be identified. Specific compositions of the raw materials of glass production indicate certain sources, technical processes and ages. Heavy minerals etc. of quartz sands contain rare earth elements (REE) from crustal fractionations that are different for the three major glass types. Accumulations of P, B, Ba, Mn and K in wood from soils by organic processes can characterize glass from certain regions.     

Aspects of the Production of Cobalt‐blue Glass in Egypt

Cobalt‐blue glass of the Near and Middle Eastern Late Bronze Age has long been recognized as compositionally distinct from other contemporary glasses (Sayre 1967; Lilyquist et al. 1993). It has been suggested recently by Shortland and Tite (2000) that this chemical distinction reflects the use of Egyptian raw materials for making these glasses, different from those used to make glass in Mesopotamia, or its manufacture by Mesopotamian workmen, possibly in Egypt. This assumed that cobalt‐bearing alum from the Western Oases and mineral natron from the Wadi Natrun were used for the cobalt‐blue glass, while the other, probably Mesopotamian, glasses were made using plant ash as the main alkali source. This note discusses some technical aspects of the possible ways in which the cobalt could have been added to the glass, and how this relates to the likely raw glass used in its making. Combining earlier suggestions by Noll (1981) and Brill in Lilyquist et al. (1993), an alternative explanation of the chemical characteristics is suggested, maintaining that all the glasses under discussion were made using plant ash. Differences in alkali concentrations probably reflect different soil and plant chemistries, and the colorant was probably added to the glass after being precipitated from the alum as a complex cobalt aluminium hydroxide.     

Analyses of Early Medieval Stained Window Glass From the Monastery of Baume‐Les‐Messieurs (Jura,France)

The collection of early medieval window glass found in the abbey of Baume‐les‐Messieurs (Jura, France) is exceptional because it dates to the end of the eighth century, and due to the number of fragments as well as their state of conservation. Different colours and forms have been identified. These pieces are a rare opportunity to address the glass craft, its recipes and techniques for a phase of its history that has remained little known. Analyses in PIXE–PIGE prove that, in addition to fragments from two soda glass items, the pieces are made from wood‐ash glass. Most of them probably came from the same production and the raw material is present in the region. At this early stage of wood‐ash glass production, the glassmakers had mastered the glass as well as the colour processes.     

The first archaeometric data on polychrome Iron Age glass from sites located in northern Italy

A large sample set of transparent and opaque glass artefacts recovered from Etruscan contexts in northern Italy (Bologna and Spina (FE) necropoleis) and dated to a period between the 6th and 4th century BC are analysed in this paper. Samples of highly decorated beads, spindle whorls and vessels of the ‘Mediterranean Group I’ (Alabastron, Oinochoes, Amphoriskos) were selected in order to determine whether these different glass artefacts were produced at the same manufacturing site. While the vessels almost certainly originate from Greece, the beads could derive from a more ancient local production ascertained at the site of Frattesina (Rovigo, Italy) and dated to the Bronze Age.     

ANALYSIS OF FIRST MILLENNIUM bc GLASS VESSELS AND BEADS FROM THE PICHVNARI NECROPOLIS,GEORGIA*

The Pichvnari necropolis on the Black Sea coast of Georgia lies in an area known in the late first millennium as ‘Colchis’, on part of the trade route leading to the Orient. The burials of the necropolis date to the late fifth century bc and frequently contain grave goods, including extremely well‐preserved polychrome glass beads and core‐formed vessels. This paper presents a study of these vessels both stylistically and archaeologically and using SEM–WDS and LA–ICPMS. It reveals that the vessels have compositional differences that may point to multiple manufacturing sites. One of the vessels appears stylistically unique and may exhibit one of the earliest uses of manganese as a decolorizer. Major and minor element data for the vessels suggest that they may belong to the same ‘Levantine’ group as many Roman glass objects, suggesting that a source of sand on the coast of the Levant could have been used in their production. The beads clearly show glass with both natron‐ and plant ash‐based flux with distinct rare earth compositions, showing multiple sites of production, some of which were probably either in the Middle East or the Indian subcontinent.