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.

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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40494-021-00505-4.

Ex novo development of lead glassmaking in early Umayyad Spain.

This study investigates glass finds from the Iberian Peninsula as a proxy for identifying the mechanisms underlying technological transformations and innovation in the wake of the Arab conquest in the seventh and eighth centuries CE. High-resolution laser ablation inductively coupled plasma mass spectrometry data combined with lead isotope analyses of a precisely dated (mid-eighth century to 818 CE) glass assemblage from the Rabad of Saqunda in Cordoba, capital of Umayyad Spain, enabled us to trace the origins of an Iberian glassmaking industry and to unambiguously link it to the exploitation of local raw materials. The analytical data reveal increased recycling, some isolated imports of Islamic plant ash glasses from Mesopotamia, and, most notably, the development of a new type of glassmaking technology that resorted to the use of lead slag from silver and lead mining and processing in the region around Cordoba. The production of this type of lead glass from Saqunda was short-lived and was subsequently refined by introducing additional fluxing agents. The technological innovation of Islamic glassmaking in Spain evidently drew inspiration from adjacent high-temperature technologies. The revival of glass and the development of a local glassmaking tradition was indirectly related to the wider processes of Islamization, such as the introduction of glazed ceramics that are compositionally related to the lead glasses from Saqunda.

Glass import and production in Hispania during the early medieval period: The glass from Ciudad de Vascos (Toledo).

One hundred and forty-one glass fragments from medieval Ciudad de Vascos (Toledo, Spain) were analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The glasses fall into three types according to the fluxing agents used: mineral natron, soda-rich plant ash, and a combination of soda ash and lead. The natron glasses can be assigned to various established primary production groups of eastern Mediterranean provenance. Different types of plant ash glasses indicate differences in the silica source as well as the plant ash component, reflecting changing supply mechanisms. While the earlier plant ash groups can be related to Islamic glasses from the Near East, both in terms of typology and composition, the chemical signature of the later samples appear to be specific to glass from the Iberian Peninsula. This has important implications for our understanding of the emerging glass industry in Spain and the distribution patterns of glass groups and raw materials. The plant ash that was used for the Vascos glasses is rich in soda with low levels of potash, similar to ash produced in the eastern Mediterranean. It could therefore be possible that Levantine plant ash was imported and used in Islamic period glass workshops in Spain. Unlike central and northern Europe where an independent glass industry based on potassium-rich wood ash developed during the Carolingian period, the prevalence of soda ash and soda ash lead glass on the Iberian Peninsula indicates its commercial and technological interconnection with the Islamic east. Our study thus traces several stages leading to the development of a specifically Spanish primary glassmaking industry.