Periodic Reporting for period 4 - GlassRoutes (Mapping the First Millennium Glass Economy)
Reporting period: 2020-04-01 to 2021-03-31
Major lines of research were concerned with the transformation of the medieval glass economy, the range of Byzantine high boron glass, the spread of Islamic plant ash glassmaking, and the identification of compositional discriminants to distinguish regional production groups. Islamic plant ash glass can be differentiated by multidimensional comparisons of a combination of trace elements and a large-scale approach based on high-resolution compositional data. The approach revealed substantial regional differences in the organisation and scope of the glass industry alongside more global developments in the economic connectivity and interregional exchange. Many of these transformations already began shortly after the disintegration of the Western Roman Empire, but gathered pace after the Arab conquest as commercial activities shifted to Damascus and Greater Syria in the late seventh century CE, and again after the establishment of Baghdad as the Abbasid capital. GlassRoutes demonstrated how geopolitical trends have consistently had an impact on the production and trade of glass in the medieval Mediterranean.
By the 10th century, soda-rich plant ash glass was produced across the Islamic world. To classify Islamic plant ash glass, we adopted a large-scale comparative approach and analysed numerous early Islamic glass assemblages, including Samarra (Iraq) and Merv (Turkmenistan), more than 1,000 tesserae from the Great Umayyad Mosque in Damascus (Syria) and Khirbat al-Minya (Palestine), a large number of glass weights from Egypt, and several glass assemblages from al-Andalus and Sicily. We were able to establish a chronological and geographical model of early Islamic glass production in Egypt. The compositional features of the mosaic tesserae from Greater Syria have brought to light the extensive trade of glass between the Levantine coast and Egypt and shown that the switch from natron glassmaking to a soda ash recipe in Syria did not occur until the turn of the 9th century. This change in glassmaking was preceded by the import of considerable quantities of Egyptian glass in the 8th century, and the relocation of the Abbasid capital to Baghdad.
Another major goal of the project was to determine glass consumption in al-Andalus and the advent of Iberian primary glassmaking. Chemical analyses of numerous glass assemblages reveal a diachronic sequence of technological and cultural developments and changes in the connectivity of the Iberian Peninsula. The glass compositions of the Roman and late antique periods are in line with the general trends observed across the Roman Empire in that the assemblages are characterised by the presence of Levantine and Egyptian natron glass. Glass becomes increasingly rare in the wake of the Muslim conquest of the Iberian Peninsula (711-714 CE). In a recent study of the glass from Šaqunda/Cordoba (756 – 818 CE), published in PNAS, we identified different stages in the transformation of the archaeo-vitreous record of the Iberian Peninsula. The glass assemblage as a whole shows a reduction in the absolute quantities of glass and an increase in recycling, indicating a disruption of supplies from the eastern Mediterranean. The lack of imports may have been the cause for experimentation and the development of a special type of lead glass production, using local resources in the form of vitreous slag from lead and/or silver mining. This recipe was further refined to produce a quintessentially Iberian soda-ash lead glass that dominates the archaeo-vitreous record of Cordoba in the 10th century.
In summary, we substantially expanded the corpus of first millennium glass compositions. From these data we have reconstructed the transformations of the Islamic glass industry and the multifarious relationships between technological changes and wider socio-cultural and geopolitical developments in the medieval Mediterranean.