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.     

Combined Pb–Sr isotopic analysis in provenancing late Roman iron raw materials in the territory of Sagalassos (SW Turkey)

In early Roman times, iron was likely supplied to the city of Sagalassos through the smelting of close-by hematite ores. In the early Byzantine period, magnetite–titanite placer sands in some instances could have been exploited for its iron. For the intermediate late Roman period, however, the source of the locally used iron was unknown. Pb and Sr isotopic analyses of iron ores from the area of Camoluk, just south of the territory of Sagalassos, and of late Roman iron artefacts from the antique city itself, reveal a very close resemblance. This makes the use of the Camoluk ores to supply Sagalassos with raw iron in the late Roman period likely. It is also shown that combined Pb and Sr isotopic analyses provides a powerful tool to distinguish chronological groups of iron provenance and a technique that can determine the nature and source of iron raw materials used.     

A geochemical study of Roman to early Byzantine Glass from Sagalassos,South-west Turkey

The finding of glass chunks together with fuel ash slag and kiln fragments related to glass processing strongly suggests local secondary production (working) of glass at Sagalassos (SW Turkey) from imperial to early Byzantine times. Chemical evidence shows that different silica raw materials were used in imperial and early Byzantine times for blue and green glass found locally. Colourless glass shows no clear difference in chemical composition and hence in silica raw materials between late Roman and early Byzantine times. Locally found early Byzantine yellow-green glass and chunks correspond to the previously defined Byzantine HIMT glass type. The chemical composition of the glass chunks found, identical to that of the contemporary glass of the same colour, strongly indicates that these chunks were used for the manufacture of early Byzantine green, colourless and yellow-green glass at Sagalassos.The homogenous lead isotopic composition of the chronological groups of blue glass, suggests the use of two distinct but homogenous silica raw materials for the manufacture of this glass. In view of this homogeneity, it is likely that contemporary blue glass was produced at a single location. The linear trend of the heterogeneous lead isotopic composition of the green and colourless glass is a strong indication of recycling effects in the glass composition. The end members of this trend are formed by the isotopic composition of the blue glass on the one hand, and of the yellow-green (HIMT) glass on the other hand. The heterogeneous lead isotopic composition of the yellow-green glass at Sagalassos is probably the result of recycling of this glass, reflecting mixtures of the original lead isotopic signatures of the broken glass and the original HIMT glass chunks.It should be noted that the two main raw materials for primary glass production (silica and soda) were available on the territory of Sagalassos. Moreover, the lead isotopic composition of quartz pebbles sampled from the artisanal quarter of Sagalassos, is similar to that of the local blue glass.     

Innovation and tradition in the fourth century mosaic of the <Emphasis Type="Italic">Casa delle Bestie Ferite</Emphasis> in Aquileia,Italy: archaeometric characterisation of the glass tesserae

The present paper focuses on the archaeometric characterisation of 38 glass tesserae of various colours from an in situ mosaic in Aquileia, Italy, dated to the second half of the fourth century AD. The examination of the textural, mineralogical and chemical features, conducted by means of a multi-methodological approach (optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), electron probe micro analysis (EPMA), X-ray diffraction (XRD) and Fibre Optic Reflectance Spectrophotometer (FORS)), has provided valuable insights into the changes in the production technology during the transition between the Roman and the Late Antique periods. The assemblage is heterogeneous, and each chromatic group is composed of tesserae produced with different base glasses and colouring/opacifying techniques, suggesting diverse supplies. A small group of tesserae shows strict links to the Roman tradition in terms of both base glass and colouring/opacifying techniques and was probably obtained by re-using tesserae from older mosaics. Conversely, a larger group of tesserae shows textural and chemical evidence of recycling and indicates the prompt use of “new” opacifying technologies (such as the use of tin compounds) or uncommon technological solutions (such as the use of quartz and bubbles as opacifiers or the addition of metallurgical slags in red tesserae), suggesting a specific production in the fourth century AD.     

TRACING THE RESOURCES OF IRON WORKING AT ANCIENT SAGALASSOS (SOUTH‐WEST TURKEY): A COMBINED LEAD AND STRONTIUM ISOTOPE STUDY ON IRON ARTEFACTS AND ORES*

Lead and strontium isotope analyses were performed by thermal ionization mass spectrometry (TIMS) on Roman to Byzantine iron artefacts and iron ores from the territory of ancient Sagalassos (south‐west Turkey), to evaluate Pb and Sr isotopes for provenance determination of ores for local iron production. It can be demonstrated that for early Roman artefacts and hematite iron ore processed in early Roman times from Sagalassos proper, as well as for magnetite placer sands and early Byzantine raw iron from the territory of the city, Sr isotopes are much less ambiguous than Pb isotopes in providing clearly coherent signatures for ore and related iron objects. Late Roman iron objects were produced from iron ores that as yet remain unidentified. Early Byzantine iron artefacts display more scatter in both their Pb and Sr isotope signatures, indicating that many different ore sources may have been used. Our study demonstrates that iron objects can be precisely analysed for their Sr isotopic composition, which, compared to Pb isotopes, appears to be a much more powerful tool for distinguishing between chronological groups and determining the provenance of raw materials.     

Supply routes and the consumption of glass in first millennium CE Butrint (Albania)

Archaeological, historical and analytical evidence can identify trade patterns and the movement of people and products and thus reveal the cultural and economic connections that existed at a given time. In the case of first millennium CE glass, the manufacture of raw glass in a limited number of glass making installations with unique compositional characteristics makes it possible to trace the likely origin of the raw materials at consumption sites. In this way the analytical characterisation of a large corpus of glass finds can identify changes in the supply routes of high-end industrial products from the Roman to the middle Byzantine period.     

The palaeo-Christian glass mosaic of St. Prosdocimus (Padova,Italy): archaeometric characterisation of ‘gold’ tesserae

A systematic and extensive archaeometric study was carried out on the loose polychrome tesserae of the palaeo-Christian glass mosaic which decorated the votive chapel of St. Prosdocimus in Padova until its replacement by the current frescoes of Renaissance age and which is one of the only two known in the Veneto region (Italy). In particular, the present paper focuses on the ‘gold’ tesserae, i.e., tesserae with a metal foil, usually composed of gold, and characterised by transparent glass not deliberately coloured or decolourised. The main research aims were the identification of the ‘base composition’ of the glass used for mosaics and the reconstruction of production techniques. In addition, comparisons with major compositional groups identified in the literature allowed us to contextualise Paduan ‘gold’ tesserae in the wider context of glass production in the 6th century AD. The compositional characterisation of Paduan ‘gold’ tesserae, carried out by means of EMPA and LA-ICP-MS analyses, showed that most of the glass samples were obtained with natron as flux, although the coexistence of various production technologies and the extent of recycling, which confirm the 6th century AD as a period of technological transition, are documented. Identification of some soda ash tesserae also allowed us to attest Medieval restoration operations. The good match between compositional groups identified in the literature for glass vessels and compositional groups identified in the ‘gold’ tesserae suggests technological links between these two production types. The chemical similarity between ‘gold’ tesserae from Ravenna and some from Padova also links production technologies in these two towns during the 6th century; coupled with the results of the historical-artistic study, these factors provide further evidence to the hypothesis that the Paduan production was mainly influenced by the nearby city of Ravenna, the capital of Byzantine mosaics in Italy.     

Variety of Black and White Limestone Tesserae Used in Ancient Mosaics in Slovenia

This study concerns the microfacies characterization of white and black limestone tesserae from selected Roman floor mosaics in Slovenia, with the aim of defining their provenance. We investigated 42 tesserae from 15 different mosaics from the archaeological sites of Ljubljana, Izola, Mo?nje, Ptuj, ?rnomelj and ?entpavel, dated from the first century bc to the fifth century ad . Among the studied tesserae, 13 different microfacies were identified: eight black and five white. The most common were mudstones with ostracods (65% of black tesserae) and wacke‐packstones with miliolids (85% of white tesserae). The majority of the identified facies can be found in the Cretaceous successions of the Dinaric Carbonate Platform in south‐western Slovenia, north‐eastern Italy and south‐eastern Croatia, suggesting a regional or imported origin of the tesserae.     

The palaeo-Christian glass mosaic of St. Prosdocimus (Padova,Italy): archaeometric characterisation of tesserae with antimony- or phosphorus-based opacifiers

The present paper reports the results of archaeometric characterisation of the opaque tesserae, intentionally coloured with antimony- or phosphorus-based opacifiers, coming from one of the two only palaeo-Christian glass mosaics known in the Veneto region (Italy), i.e., the mosaic which decorated the votive chapel of St. Prosdocimus in Padova. In particular, 55 tesserae belonging to glass types “White”, “Blue”, “Yellow”, “Green” and “Brown” are examined here. The multi-methodological approach (SEM-EDS, EMPA, XRPD, imaging spectroscopy coupled, in some cases, with XAS) gave valuable insights into the complexities of palaeo-Christian glass mosaic production technologies. Two main groups are identified, one characterised by glassy matrixes and opacifiers (calcium or lead antimonate) typical of the Roman period and comprising all “White”, “Blue”, and “Yellow” tesserae and some “Green” ones, and the other characterised by glassy matrixes and an opacifier (calcium phosphate) typical of the 6th century AD, composed of “Green” and “Brown” tesserae. This suggests that, during that century there was a gradual change from older to “new” production technologies: although new opacifiers such as calcium phosphate started to be used, the frequent use of antimony-based ones (43/55 samples) supports the hypothesis that their systematic use was extended until the 6th century, although re-using old tesserae cannot be completely excluded. In addition, comparisons with compositional groups already identified in the “gold” tesserae of the same mosaic and tesserae from Ravenna demonstrate that both the same “base compositions” of the glass were used to produce transparent and opaque glass. This evidence, coupled with the results of the historical-artistic study, suggests technological connections between Padova and Ravenna, the capital of Byzantine mosaics in Italy. Micro-structural observations and chemical analyses of the Paduan antimony-based opacified glass demonstrate that different processes and raw materials were used in their production. Both in situ and ex situ crystallisation can be identified for calcium and lead antimonate in Paduan tesserae, whereas the production of tesserae opacified with calcium phosphate generally appears to be highly standardised. Although the opacifiers used in the Paduan tesserae support technological transitions, the colouring elements identified here, i.e., iron and manganese for white, yellow, brown and some green tesserae, cobalt for blue, and copper for blue and green, suggest continuity, because their use is widely testified in the production of both transparent and opaque glass artefacts dating from the Bronze Age until Medieval times, from whichever archaeological site the samples come. Peculiar relationships among the oxidation states of colouring elements, their contents in the glassy matrix, the types of opacifiers used, and the final colour of tesserae were identified. In addition, the correlations of cobalt and/or copper with other elements, together with identification of relics of colouring and “metallic” droplets, allow us to speculate on possible sources and production technologies. Lastly, identification of newly formed crystalline inclusions in tesserae also yields information on kiln temperatures, which ranged between 900 and 1150 °C, a range easily reached in the furnaces of the 6th century AD.     

Glass and metal analyses of gold leaf tesserae from 1st to 9th century mosaics. A contribution to technological and chronological knowledge

An archaeometric study was carried out on 40 gold leaf tesserae from mosaics in Italy dated 1st to the 9th century AD. Glass layers and gold leaf were both analysed by X-ray microanalysis. The main aim was the identification of the composition of the glass and of the gold leaf, in order to assess the variations in composition and nature of the tesserae in the examined period.     

A STUDY OF GLASS TESSERAE FROM MOSAICS IN THE MONASTERIES OF DAPHNI AND HOSIOS LOUKAS (GREECE)

In this work 51 glass mosaic tesserae from decorations of the two Greek monasteries of Daphni and Hosios Loukas were analysed by inductively coupled plasma optical emission spectroscopy, electron microprobe analysis and X‐ray powder diffraction. On the basis of the chemical analyses, after discrimination between the tesserae of the original decorations and those from other periods, it was possible to outline the distinctive traits of Byzantine mosaic tesserae. In both the monasteries, the original mosaics were decorated with tesserae produced with plant ash based glass, either of the typical composition or a mixture with natron type glass. The samples from the Hosios Loukas decorations show a more homogeneous composition compared with those from Daphni. The major differences among the original samples are due to the presence of opacifiers and colourants.     

Florence baptistery: chemical and mineralogical investigation of glass mosaic tesserae

A recent restoration of the mosaics of the Baptistery in Florence enabled the collection and analysis of a group of glass tesserae. Twenty-three tesserae, dated between the end of the 13th century and the first half of the 14th century, showing different colors were sampled and analyzed to identify the raw materials, colorants and opacifiers employed in their production.     

On Early Thimbles: A Seventh‐Century‐AD Example from Punta Secca,Sicily, in Context

A copper‐alloy thimble was found in 2010 at Punta Secca, Sicily, in a sealed context datable by coins to the first quarter of the seventh century AD. It has generally been thought that thimbles did not reach the Mediterranean area until the ninth century AD, but at least nine metal examples are in fact attested at various places from contexts datable between the late sixth century and the early ninth. It is suggested that the increasing use of silk in clothing in the Byzantine Empire during the seventh century, probably accompanied by the use for the first time of steel needles which made the use of a finger protector imperative, explains the apparent introduction of thimbles at this time. No securely dated metal thimbles are known from sites of Roman date, except for one at Ephesus of c.AD 100. It is very tentatively suggested that this last example might represent an import from China, where thimbles (and steel needles) are attested from at least the third century BC onwards.     

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.     

Chemical composition characterization of ancient glass finds from <Emphasis Type="Italic">Troesmis</Emphasis>—Turcoaia,Romania

This paper reports and discusses the chemical composition of 20 glass fragments discovered during the 2012 archeological survey at Troesmis (Turcoaia, Tulcea county, Romania) and dated to the Roman and the Byzantine/Early Medieval periods. The data were obtained by two external Ion beam analysis (IBA) methods—namely Particle-induced X-ray emission (PIXE) and Particle-induced gamma-ray emission (PIGE)—and they were compared to the recognized compositional glass groups from the Mediterranean region during the first millennium AD. The Troesmis assemblage turned out to contain samples belonging to several distinct categories of ancient glass, obtained from different raw materials and manufacturing procedures. Some of the analyzed vitreous finds from Troesmis were the result of glass recycling, while others were identified as deriving from Roman glass vessels imported from the Levantine or Egyptian shores of the Mediterranean. This archeometric study brings additional arguments for the long-range commercial exchanges during the Roman period.     

Byzantine glass mosaic tesserae: some material considerations

Abstract

Issues about the manufacture of Byzantine mosaics and the implications of these in wider terms relating to social and economic questions about the art form have been little discussed. This paper brings together evidence about Byzantine glass mosaic tesserae gathered from archaeology, glass technology and glass analysis, and synthesizes these into a discussion of three aspects: distribution; manufacture; trade and price. It looks to examine how these different elements can be used to form a more detailed composite picture about the production and distribution of Byzantine mosaics. It also proposes ways in which glass analysis can be used in a more coherent way to extend our understanding of mosaic glass production.     

Beads from a mediaeval pilgrim centre: Chemical composition and provenance of glass from Banganarti,Nubia, Sudan

Christian Nubia was a region with intensive transcultural connections that are visible through the understudied overseas glass bead imports found there. This paper presents the results of an analysis of 20 glass beads from Banganarti, a Christian pilgrim site active during the Makuria kingdom (mid-sixth to 14th centuries CE). Compositional analyses using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) have identified glass belonging to a number of broad compositional groups. Two beads were made of mineral soda-lime glass, dated before the mid-ninth century CE. Numerous beads were made from plant ash-soda-lime glass associated with “Mesopotamian” production dated between the eighth and 10th centuries CE. Lead-soda-silica glass has parallels in the ninth–10th centuries glass found in Africa and Europe. One plant ash-soda-lime bead was of eastern Mediterranean origin dated after the 10th century CE. Results of this study provide new evidence for provenance and chronology of glass beads available in the mediaeval Northeast Africa as well as contribute new data to the research on the pilgrim and/or trade routes of that time.     

Faecal biomarker and archaeobotanical analyses of sediments from a public latrine shed new light on ruralisation in Sagalassos, Turkey

A public latrine in the ‘Imperial Baths’ of Sagalassos was transformed into a dump site in the early Byzantine period. Several layers of urban waste, including ceramics, bones, glass and perhaps excrements were deposited on the floor. Faecal biomarker analyses and archaeobotanical analyses were conducted to reconstruct the history of the room. 5β-stanols of human origin, such as coprostanol, were found in the sewage channels together with mineralised plant remains, indicating a human faecal context. The botanical remains are furthermore representative of the Roman diet of the Sagalassians. Soil layers, deposited on top of the latrine floor and dating to the early Byzantine period, contained herbivore derived 5β-stanols, such as 5β-stigmastanol and epi-5β-stigmastanol. Additionally, a clear predominance of epi-5β-stanols over 5β-stanols showed that the animal dung has been subject to composting. In this period, the former latrine was clearly used as a manure production site which is further confirmed by stratigraphic evidence of large amounts of urban waste artefacts, which were commonly collected together with manure before application on the fields. The results of the present study support the theory that off-site potsherd scattering can be used as a proxy for manuring events. Additionally, the data show key evidence for vertical migration of 5β-stanols and presumably also for the leaching of bile acids.     

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.