Plant Ash Glass Research Articles

Glass Finds from the Elite House of Roue, a Sasanian City Building in Western Iran: Composition and Classification Using XRF and Raman Spectroscopy

The Silk Road connected the east of Iran to the western world. Roue city is close to the Road. Six glass samples from Roue were classified on the basis of morphology, archaeological context and compositions. The samples were analysed by means of XRF and Raman spectroscopy and two specific groups, namely Roue type 1 and Roue type 2, with close composition to high alumina plant-ash glass in circulation from the 6th to 10th centuries CE in Mesopotamia, Iran and Syria, were identified. The simultaneous occurrence of two types of glass in the excavated layers shows that the house was inhabited in the early Islamic period. Colours (black, amber-green, light and aqua blue) were produced mainly by the amount of iron and sulphur ions required for the amber chromophore and copper ions for the blue colour and the controlling of reducing conditions in the furnace.

Glass working and recycling in Pompeii: new evidence from the landfill of the Sarno Baths (VIII 2, 17–23)

Forty-six glass finds, including vessel fragments, windows, one inlay and one indicator of production (moil) excavated in the dump of the Sarno Baths in Pompeii were selected for an interdisciplinary technological, typological and chemical study. The identification of the moil demonstrates that a glassblowing workshop most likely existed in Pompeii, thus putting an end to a long-standing scientific debate. The LA-ICP-MS chemical data show that Roman-Mn base glass predominates, along with few Egyptian natron-type glasses and some plant-ash glass of probable Egyptian origin as well. A large proportion of the analysed glass, including the moil, consists of recycled compositions, suggesting the existence of an efficient system of collection and recycling of glass, which was active even at a time when the city had an abundant supply of fresh glass. The demand for raw glass in Pompeii far exceeded the average demand of other Roman towns, because glass containers were essential for the flourishing perfume industry in Pompeii and Campania. The proximity of the Sarno dump to the perfume district in the south-western part of the city and to the horrea of the Sanctuary of Venus suggests the possible location of the glass workshop in this area.

Soda-lime glass trade across the Eurasian Steppe during the 4th to 5th century CE: Evidence from a Xianbei cemetery in Inner Mongolia

A batch of glass beads, including silver-in-glass beads and monochrome beads from the Chenwugou cemetery in Ulanqab, Inner Mongolia, China was analysed using optical microscopy (OM), Scanning Electron Microscopy-Energy Dispersive Spectrometry (SEM-EDS), Laser Ablation Inductively Coupled Plasma Atomic Emission Spectrometry (LA-ICP-AES), and Mass Spectrometry (LA-ICP-MS). Based on their compositions, the silver-in plant ash glass samples are chemically very homogenous and possibly from Iran/Central Asia, if they were not made locally in China. The four monochrome beads are all individually different, with three plant-ash glasses and one natron glass bead thought to be from the southeastern Mediterranean. The silver-in-glass beads were made from a drawn glass tube as the inner layer, with a silver foil on its surface. They were then covered by another glass layer richer in iron oxide, before being cut into beads in a mould.

Geochemical variations in early Islamic glass finds from Bukhara (Uzbekistan)

Glass manufacturing processes and recipes changed fundamentally after the 8th century CE. The earlier centralised production system diversified, primary production sites multiplied, and the scale of individual productions contracted. Mineral soda was no longer used and instead replaced by plant ash as the main fluxing agent, affecting the chemical composition and properties of the glass. In this work, LA-ICP-MS and Raman spectroscopy were used to investigate the compositional and structural characteristics of 68 glass fragments recovered during recent excavations at Bukhara in Uzbekistan, dating to the 9th to early 11th centuries CE. This is the most extensive systematically collected and studied glass assemblage from Central Asia to date. The glass can be attributed to different origins, confirming on the one hand the diversification of glass production during the early Islamic period and, on the other hand, regional variations in the chemical compositions and network structure of soda-rich plant ash glasses. As clear archaeological evidence for early Islamic glass production sites in Central Asia is rare, regional production groups are distinguished primarily on relative concentrations of Mg, K, P, Cl, Li and Cs in relation to the plant ash component, while variabilities in Al, Ti, Cr, Y, Zr, Th and REEs and their ratios indicate different silica sources. Raman spectra suggest variations in network connectivity and Qn speciation that confirm compositional groupings and suggest structural differences between regional productions of plant ash glass. The results demonstrate a clear dominance of local or regional glass groups, while revealing the importation of Mesopotamian glass, notably a high-end colourless glass type from the region around Samarra in Iraq. The new analytical data allow further separation and characterisation of novel early Islamic plant-ash glass types and their production areas.

Connected in diversity: Isotopic analysis refines provenance for Islamic plant-ash glass from the eastern Silk Roads

Our understanding of glass production in Eurasia has been built mostly on evidence from Europe and the Mediterranean. Here, we investigate the occurrence and organization of plant-ash glass production in the eastern continental Islamic region, focusing on an 11th-12th century assemblage unearthed in Shadyakh, Nishapur, Iran. Through Sr-Nd isotope analysis and by examining geochemical contexts and mixing patterns, we find that distinct silica and ash sources originating from Tigris-Euphrates Basin, Central Asia, and potentially Iran were used to make these objects. Zagros-derived silica and Central-Asian-type silica were likely important silica sources for Islamic plant-ash glasses from east of the Tigris. Furthermore, we show that Central Asian glass can be characterized by chemical and isotopic signatures, while Iranian glass may exhibit overlapping signatures with glass from neighboring regions. The plant-ash glass industry in Islamic-period West and Central Asia likely thrived by exploiting and sharing diverse, regionally characteristic raw material sources.

Unique wood ash Co-coloured glass tessera from mediaeval Madonna: Raman spectroscopic study of production technology

While the natron and plant ash glass tesserae may be found on places of importance across the former Roman and Byzantine empires, wood ash glass tesserae are scarce. This is the first time a wood ash glass tessera is studied in detail. It was part of a magnificent 8-metres tall statue of Madonna in Malbork, Poland, created at the end of the 14th century and destroyed at the end of World War Two. It was found to be coloured by cobalt with possible impact of copper, and opacified by Ca-phosphate. Processes previously described in sodium-rich glasses were observed also in the studied potassium-rich wood ash glass tessera, such as diffusion of the respective alkali metal into the Ca-phosphate grains. The elemental composition of the tessera indicates that it is original – mediaeval, from the area north of Alps. Two phases were identified for the first time, to authors’ best knowledge, in any glass tessera – leucite (tetragonal KAlSi2O6) and pseudowollastonite (monoclinic CaSiO3). As pseudowollastonite is a high-temperature phase, it may serve as an indicator of production temperature, which was further supported by the study of polymerisation index of model glasses. This study contributes to the knowledge of old technologies and showed that the know-how for opacification was imported from the Mediterranean, while the raw materials employed for the base glass preparation were from the area north of Alps.

Early Islamic glass (7th- 10th centuries AD) in Unguja Ukuu, Zanzibar: A microcosm of a globalised industry in the early 'Abbasid period.

Eighty-two glass vessels, recovered from the excavations at the ancient Swahili settlement and port of Unguja Ukuu in Zanzibar, Eastern Africa, were analysed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results show that all of the glass samples are soda-lime-silica glass. Fifteen glass vessels belong to the natron glass type and are characterised by low MgO and K2O (<1.50%), suggesting they were made from natron, a mineral flux that was widely used during the Roman period and Late Antiquity. Sixty-seven glass vessels belong to the plant ash glass type, characterised by high magnesia and potash levels (>1.50%), suggesting plant ash was the main alkali flux. Based on the major, minor and trace elements, three different compositional groups were identified for the natron glass and three were identified for the plant ash glass: (1) UU Natron Type 1, (2) UU Natron Type 2, (3) UU Natron Type 3, (4) UU Plant ash Type 1, (5) UU Plant ash Type 2 and (6) UU Plan ash Type 3. Comparison with contemporary Middle Eastern glass groups shows that UU Natron Types 1, 2 and 3 correspond to Egypt II high Na2O, Levantine I and Levantine II respectively, while UU Plant ash Type 1 matches closely with Samarra Group 2. UU Plant ash Types 2 and 3 have unique chemical fingerprints that do not match any of the contemporary plant ash glass groups, but their chemical compositions show some affinity with the old Sassanian plant ash glass, suggesting a possible Mesopotamian provenance. Combined with existing research on early Islamic glass, the authors reveal a complex trading network in the globalisation of Islamic glass, particularly involving glass corresponding to modern Iraq and Syria, in the 7th- 9th centuries AD.

The dating and provenance of glass fragments from the site of Serabit el-Khâdim, Sinai

Serabit el-Khâdim, located on the western coast of the Sinai Peninsula, is the site of an ancient turquoise mine established in the early 12th Dynasty (c. 1985 BCE) and active between the 18th and 20th Dynasties (c. 1550–1136 BCE). The temple dedicated to Hathor at Serabit detail the number of offerings made, thereby recording the level of activity at Serabit during each reign. The last offerings were made by Rameses VI (1143–1136 BCE) corresponding with the collapse of the Late Bronze Age before the site was abandoned. 976 glass fragments were given to the Ashmolean Museum by Flinders Petrie following his 1905–6 excavations. 41 fragments from the collection were selected for LA-ICP-MS analysis with the aim of provenancing and dating an unknown collection of glass using composition and available stylistic features to further narrow the date of manufacture and therefore indicate the possible workshop of origin. The analysis showed that all 41 fragments are of Egyptian provenance and of standard Late Bronze Age high magnesia plant ash glass, except one fragment which is a unique example of natron blue glass applied as decoration to a white plant ash vessel body. Subtle compositional differences show that 18th Dynasty plant ash glass, plant ash Ramesside glass and natron Ramesside glass are all present, therefore corresponding with the known Egyptian activity at Serabit.

Glass from the 11th–13th century medieval castle of San Giuliano (Lazio Province, Central Italy)

Compositional analysis of glass from the medieval castle of San Giuliano (Lazio, Italy), occupied from approximately CE 1050–1250, sheds light on the financial wherewithal and integration of the castle’s elite inhabitants into wider economic networks. Portable X-ray fluorescence (pXRF) of 261 shards was used to select 32 for further analysis using wavelength dispersive electron microprobe analysis (EMPA-WDS). This compositional analysis documents the pervasive recycling of earlier glass cullet, some of which pre-dates the 4th century CE. Around 20% of the sample comprised primarily plant ash glass, evidencing the penetration of plant-ash glasses into inland sites on the western central Italian peninsula. Almost 60% of the shards were an intermediate glass combining more recent plant ash glasses with recycled natron-based glass cullet derived from the Roman and Early Medieval periods. Compared to glass assemblages from contemporaneous sites, the levels of both recycled and intermediate glasses are quite high, with a concurrent incidence of trace elements that further precluded the manufacture of perfectly translucent glass vessels. This suggests that while the residents of the castle desired glass as a symbol of prestige, they may not have had the economic resources to obtain glass of the highest quality.

A large-scale Sr and Nd isotope baseline for archaeological provenance in Silk Road regions and its application to plant-ash glass

Bioavailable Sr and detrital Nd isotopes are important tools for archaeological provenance. To apply Sr and Nd isotopes for provenance, regional isotope databases and baselines are generally needed. For the vast Silk Road regions of Mesopotamia, Iran, and Central Asia, detailed isotopic distribution patterns essential for determining provenance may not become available in the short term due to the severe deficiency of available data. In the present work, we investigate the geo-environmental factors controlling the Sr and Nd isotopic signatures and use published data from archaeology and Earth sciences, selected by rigorous criteria, to construct the first large-scale, semi-quantitative Sr–Nd isotope baseline for these Silk Road regions. Three isotopic zones are proposed for Central Asia: CA-1 (mountains), εNd < −7.5, 87Sr/86Sr > 0.7095; CA-2 (deserts), εNd = −5 to −2, 87Sr/86Sr ∼ 0.709; CA-3 (loess), εNd = −5 to −2, 87Sr/86Sr > 0.710. General isotopic signatures are suggested for Iran: εNd = −8 to −4, 87Sr/86Sr = 0.7075–0.7090. Three isotopic zones are proposed for Mesopotamia: MP-1 (floodplain and foothill), εNd = −6.5 to −4 (putative extended range MP-1N, εNd = −8 to −6), 87Sr/86Sr = 0.7080–0.7085; MP-2 (deserts), εNd < −8, 87Sr/86Sr > 0.7085; MP-3 (Syrian Euphrates), εNd = −5.5 to −2, 87Sr/86Sr = 0.7080–0.7085. Within the limitation of available data, these ranges indicate the overall trend of bioavailable Sr and detrital Nd isotopic signatures for each isotopic zone, which are controlled by their geological context, climate (e.g., precipitation), and various Earth surface processes (e.g., riverine versus aeolian transport). This baseline can be used as an essential guide for geochemical contexts to suggest or verify the provenance of plant-ash glass, serving as part of an integrative Sr–Nd isotopic approach. We illustrate the potential of this approach using two case studies. By investigating the isotopic compositions of Mesopotamian plant-ash glass, we suggest possible northern Mesopotamian origins for plant ash and silica raw materials used for Mesopotamian glass-making. By reassessing medieval plant-ash glass from San Lorenzo, Italy, we propose diverse origins including Central Asia and Mesopotamia. Additionally, as part of this isotopic approach, by examining the Nd isotope mixing lines in the context provided by the Nd isotope baseline, we reveal the occurrence of glass recycling for Islamic plant-ash glass from different production zones in association with a westward spread from Mesopotamia to the Eastern Mediterranean metropolises.

Compositions of early Islamic glass along the Iranian Silk Road

The composition of archaeological glass reflects the geochemical nature of its raw materials. To determine the origins and distribution of early Islamic glasses from Iran, a set of 169 glass samples from five different sites was analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of 58 elements. The glasses were classified into six different plant ash glass groups, three of which were attributed to a Mesopotamian origin, while three further groups are presumed to represent regional Iranian productions. The ratios of MgO/CaO and K2O/P2O5 of the different groups reflect variations in the plant ash component. Minor elements Cr, Ti, Zr, La and Th and their ratios proved effective in distinguishing the base glass types. Mapping their frequency across the Iranian plateau revealed the relative movement of glass and likely source areas. The decline in the frequency of glass types with elevated Cr/La ratios east of the Zagros Mountain range confirms that elevated Cr/La ratios together with an augmentation of the magnesium levels are features of Mesopotamian glass production apparently inherited from the geochemical environment of the Euphrates and Tigris river valleys. Some exceptionally clean Mesopotamian glasses made from a quartz-rich silica with low levels of accessory minerals are consistent with ninth-century glass from Samarra, which was evidently traded widely along the Silk Road network. No evidence of local glass production was detected in Nishapur. The Iranian groups were produced from a quartz-rich silica source, high in thorium but with different zirconium contents resulting in different Th/Zr ratios. Aluminium concentrations tend to increase from west to east, with the highest values found among glass assemblages from Central Asia.

Material Characteristics and Comparison of Silver Foil Glass Beads Excavated from the Tomb of King Muryeong in Korea

This study investigated the comprehensive characteristics of silver foil beads excavated from the Tomb of King Muryeong, based on composition analysis of the foil and glass and morphological characterization. The major element components of metal foil and glass were investigated using a scanning electron microscope (SEM) equipped with an Energy Dispersive X-ray spectrometer (EDS). Trace elements were determined using LA-ICP-MS to constrain the source of the raw material. The morphological characteristics of the beads were recognized through an optical microscope. As a result of the analysis, the metal foil was detected as pure in both gold- and silver-colored glass beads. The chemical composition of the glass was determined as a soda glass, with Na+ acting as a flux and CaO added as a stabilizer to improve durability. It was confirmed that plant ash was used because MgO and K2O were found to contain more than 1.5%. Through trace element analysis, it was confirmed that the gold and silver-colored silver foil glass beads were made of plant ash glass using different materials. The content of Fe2O3 was significantly higher in the gold-colored silver foil glass beads than in the silver-colored silver foil glass beads. Therefore, it can be interpreted that the gold-colored silver foil glass beads excavated from the tomb of King Muryeong intentionally achieved the appearance of gold foil glass beads by controlling the color of the outer glass. The silver foil glass beads showed morphological differences according to the color of the outer glass. The gold-colored silver foil glass beads were manufactured as single or segment types, but the silver-colored silver foil glass beads were manufactured as segment types.

Rare Alkali Elements as Markers of Local Glass Working in Medieval Tolmo de Minateda (Spain).

Analytical data of Roman and early Islamic glass established several primary glass production groups linked to glassmaking centres in the Levant and in Egypt. In contrast, the activities of secondary glass workshops are largely invisible in the compositional fingerprint of first millennium glass. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) of 261 glass finds from the Visigothic settlement of Tolmo de Minateda (Spain) revealed a site‐specific contamination pattern due to secondary glass processing and recycling, namely the enrichment of the glass batch by a unique combination of rare alkali elements (Li, K, Rb, Cs). With a median of 21 ppm, Li is particularly distinctive. Elevated lithium contents (Li>30 ppm) are also one of the characteristic features of Iberian plant ash glass from the Islamic period. The earliest known examples of this type of glass were found among the ninth‐century remains from Tolmo.

Shedding Light on Roman Glass Consumption on the Western Coast of the Black Sea.

The chemical composition of 48 glass finds from Histria and Tomis, Romania, chiefly dated to the 1st–4th c. AD, was determined using prompt gamma activation analysis (PGAA) at the Budapest Neutron Centre (BNC). Most fragments have composition typical for the Roman naturally colored blue-green-yellow (RNCBGY) glass; Mn-colorless, Sb-colorless, and Sb–Mn colorless glass finds were evidenced, too. Several Foy Série 2.1 and Foy Série 3.2 glass fragments, as well as an HIMT and a plant ash glass sample, were identified in the studied assemblage. The archaeological evidence, the glass working waste items, and the samples with compositional patterns suggestive of recycling are proofs of the secondary glass working activities at Tomis during the Early Roman Empire period.

An archaeometric perspective on selected Roman and Late Antique glass finds from Dobrudja

This paper reports the results of Prompt Gamma Activation Analysis (PGAA) analyses on 21 glass fragments discovered at Tropaeum Traiani, Carsium, Ulmetum, and Altinum, Constanţa County, Romania, dated to the 1st-6th c. AD. The chemical data indicate a broad palette of compositions: Sb-colorless, Mn-colorless, Sb-Mn colorless, typical blue-green Roman, Série 2.1 and Série 3.2 of Foy glass. A plant ash glass sample was identified – most likely a fragment of a vessel imported from the Sasanian Empire.

Supply of glass to the medieval hilltop settlement of Ultrera (Eastern Pyrenees, France)

Founded in the fifth century on a granite outcrop overlooking the deep valleys of the eastern Massif des Albères and the Roussillon coast, the hilltop settlement of Ultrera/Ultrère was strategically located to dominate the lowlands. Its position on this natural boundary between the Iberian Peninsula and Central Europe raises interesting questions about its connectivity and the circulation of materials. In the early days of rural feudalism, the emergence of the castrum led to the birth of the “feudal” castle and the first fortified villages. Ultrera was organized into several districts spread over three hectares and survived until the tenth century CE, which is an exceptionally long occupation. The present paper examines the glass supply to Ultrera throughout its history, combining typological and archaeometric approaches to study the evolution of glass compositions and the use of different raw materials through time. A series of 43 well-contextualized glass objects have been analysed for major, minor and trace elements using LA-ICP-MS. The glasses of the fifth to seventh centuries comprise mostly vessels and especially goblets. The base glass can be affiliated to previously established natron-type primary production groups (HIMT, Foy 2.1, Foy 3.2 and Levantine 1), and about half of it shows substantial signs of recycling. The ninth- to tenth-century assemblage marks a change from the previous occupation. Two beads made from a soda-rich plant ash glass confirm Islamic imports from Mesopotamia and perhaps the western Mediterranean. A linen smoother with a wood ash glass signature is the only testimony of Carolingian influences. Glass tableware is becoming increasingly rare and some of the drinking goblets are remnants from a previous phase. The progressive independence of the Catalan counties from the Carolingian Empire and the change of the glass production system towards the end of the first millennium CE may explain the absence of typical Frankish glass. Soda plant ash glass from the thirteenth and fourteenth centuries, probably from the feudal castle, indicates yet another change at the end of the Middle Ages, when there is evidence for both regional production and long distance imports.

The representation of skin colour in medieval stained glasses: The role of manganese

The present study concerns a corpus of 17 glass pieces representing character heads, originating from 11 major cathedrals and churches from North Western France and which constitute the masterpiece of stained glass windows. Skin complexion ranges from colourless to flesh-tone and purple. These glasses have been investigated using non-destructive and non-invasive techniques. Particle Induced X-ray Emission and Particle Induced Gamma Emission analyses at AGLAE show that these glass pieces show potassic plant ash glass compositions, typical to 12th −15th centuries. The compositional variability of the major glass components remains limited, similar to that found for single monuments, despite the diversity of geographic origins. The Mn and Ba concentrations follow a different trend in flesh-coloured or purple glasses and in colourless glasses, suggesting that the sources of Ba and Mn in these two kinds of glasses originated from different raw materials. Purple and flesh tone glasses contain more manganese than colourless glasses with an almost similar iron content. Synchrotron X-ray absorption near-edge structure spectroscopy (XANES) and portable UV–visible-NIR optical absorption spectroscopy indicate that glass colour varies with results from Fe2+, Fe3+, Mn2+ and Mn3+. The thickness of the glasses, about 3 mm, has been measured using ultrasound techniques. Its dispersion is similar in the various coloured glasses. This parameter mostly influences the colour saturation but not the hue. Obtaining flesh-coloured or purple glasses requires some control of the oxidation state of manganese during glass making. Divalent manganese is largely prevalent and the colour change from flesh-tone to purple hues is driven by small variations in the Mn3+ content. As these variations are not related to the Fe/Mn ratio, the resulting glass colour is difficult to predict on the only basis of glass composition. Due to the low kinetics for obtaining a redox equilibrium state between furnace atmosphere and the silicate melt, using Mn4+- and Mn3+-oxide minerals made it possible to favour oxidized melts, provided the glasses be taken out of the oven before redox equilibrium be reached: the shorter the melting time, the more oxidized will be resulting glass. This shows that medieval glassmakers were able to overcome the challenge of making glasses under highly oxidizing conditions to retaining enough oxidized manganese to favour flesh-tone and purple colours in wood-fuelled furnaces.

Gambassini on the road. Underpinning evidence for a medieval widespread glass production in the north Adriatic area

The paper discusses historic, chrono-typological and archaeometric data related to two assemblages of late medieval drinking glass vessels from the monastic complex of San Severo (Ravenna, Italy) and the castle of Rontana (province of Ravenna, Italy). Though standing as different types of settlements, the two sites are linked by the occurrence of a specific beaker among unearthed finds, known as gambassino (or ganbasino) and named after Gambassi, a location in the province of Florence, in Tuscany, believed to be the place where the manufacture of the gambassini originated. The present study, carried out through an integrated use of different disciplines, has provided insights into the production and circulation of this form, extremely common in the late medieval period. Comparative chrono-typological study highlighted no relevant morphological differences among assemblages, with recurrent sizes and decorative patterns. Archaeometric study allowed the identification of various compositional groups pointing to different vitrifying and fluxing agents, although all samples can be classified as plant ash glass; chemical data also show comparability between the gambassini from both sites here considered and Medieval glass sets from the Adriatic area found on the Italian territory and in the Balkans. The displacements of artisans and the circulation of raw materials, the recurrence of this beaker in numerous excavation contexts in the northern Adriatic area - with evidence from the Balkans and Europe - as well as the identification of compositional groups different from each other, but overlapping among assemblages, support the model of a “widespread production” of gambassini. The proposed scenario is further validated from the economic sustainability point of view, considering the production and supply of an object for everyday use and not exclusively dedicated to the élites.

Composition and origins of decorated glass from Umayyad Cordoba (Spain)

Recent archaeological excavations carried out in the western suburbs of Cordoba (Spain) brought to light numerous fragments of archaeological glass from the caliphal period (929–1031 CE). The typological and compositional analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of 66 fragments enabled the identification of different types of base glass and glass working techniques, identifying local productions, imports and decorative imitations of eastern models. The studied fragments include Mesopotamian, Levantine, Egyptian and possibly Sicilian soda-rich plant ash glass categories, and various glass-decorating techniques such as mould-blowing, pressing, cutting, staining or gilding. The systematic comparison of the trace element patterns of several relief-cut objects identified both imported ware and a locally manufactured sample, whereas all mould-blown pieces were made from locally sourced raw materials. Iberian glassworkers seem to have preferred mould-blowing, probably because of the distinct working properties of locally available high lead glass. The results thus confirm the continuous long-distance exchange of vitreous material, as well as the existence of multiple glassmaking centres in the Iberian Peninsula, illustrating a link between secondary glass working techniques and chemical composition. Furthermore, the identification of several fragments belonging to the same object based on chemical composition allowed us to reconstruct entire vessels and thereby expand the repertoire of known typologies circulating in Umayyad Spain.

Production and provenance of architectural glass from the Umayyad period.

A large assemblage (n = 307) of architectural glasses (tesserae and windows) from the early 8th-century Umayyad residential site at Khirbat al-Minya was analysed by laser ablation inductively coupled plasma mass spectrometry. Trace element patterns are essential to establish the provenance of the base glass, while the comparative evaluation of the colouring and opacifying additives allow us to advance a production model for the manufacture of glass mosaic tesserae during the early Islamic period. The primary glass types are Levantine I and Egypt 1a, as well as a few older, reused tesserae, and Mesopotamian plant ash glass used for amber-coloured window fragments. Chemical data revealed fundamental differences in the colouring and opacification technologies between the Egyptian and Levantine tesserae. Co-variations of lead and bismuth, and copper, tin and zinc in the Egypt 1a tesserae provide first evidence for the production of different mosaic colours in a single workshop, specialising in the manufacture of tesserae of different colours. No such trend is apparent in the Levantine samples. Red, cobalt blue and gold leaf tesserae were found to be exclusively made from a Levantine base glass, indicating that the generation of some colours may have been a specialised process. The same may apply to the amber-coloured window glass fragments of Mesopotamian origin that exhibit very unusual characteristics, combining elevated copper (2% CuO) with an excess in iron oxide (5% Fe2O3). These findings have significant implications for the production model of strongly coloured glass and the exploitation of resources during the early Islamic period.