Ex novo development of lead glassmaking in early Umayyad Spain

Abstract

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 Šaqunda 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 Šaqunda 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 Šaqunda.

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

“…All other elements remain below 1%, except for chlorine that is exceptionally high, ranging from about 1.3% to 2.2%. Further features include elevated arsenic, silver, tin, antimony and bismuth contents (Additional file 1 : Table S1) that suggest the use of litharge from silver cupellation as the main lead-bearing raw material [ 3 , 30 , 31 ]. Most of the soda-ash lead glass samples are colourless, while some show a greenish or yellowish tinge.…”

“…Elements related to the lead source such as arsenic (58 ppm), silver (6 ppm) and bismuth (4 ppm) are much lower than in most of the soda-ash lead samples, while it has notably higher barium (3383 ppm) (Additional file 1 : Table S1). In these characteristics the bead resembles the high lead glass from Šaqunda (Cordoba) from the late eighth to early ninth century that is assumed to have been made from lead slag from silver or lead mining processes [ 3 ]. Despite the similarities in lead oxide contents with some North African Islamic beads [ 33 ], the black opaque bead from Cordoba has higher alkaline earth elements and significant differences in major and trace elements, particularly unusually high zinc contents.…”

“…While Roman and late antique natron-type glass from Egypt and the Levant continued to prevail in the sixth and seventh centuries, glassmaking experienced a significant increase in recycling at the end of the Visigothic period, probably due to insufficient fresh glass supplies [ 1 ]. Glass finds of the early Islamic period are relatively scarce in al-Andalus, and recycling of natron glass seems to have been the main source of supply also during the first century of Islamic rule [ 2 , 3 ]. Recent work on the elemental and isotopic composition of early Umayyad glass assemblages from the late eighth and early ninth centuries identified a novel glassmaking recipe in Cordoba, using lead slag as the main ingredient [ 3 ].…”

“…Glass finds of the early Islamic period are relatively scarce in al-Andalus, and recycling of natron glass seems to have been the main source of supply also during the first century of Islamic rule [ 2 , 3 ]. Recent work on the elemental and isotopic composition of early Umayyad glass assemblages from the late eighth and early ninth centuries identified a novel glassmaking recipe in Cordoba, using lead slag as the main ingredient [ 3 ]. This new glassmaking technology appeared independently of contemporary trends in the Islamic east, but instead bears some resemblance to high lead glass from Carolingian Europe [ 3 ].…”

“…Recent work on the elemental and isotopic composition of early Umayyad glass assemblages from the late eighth and early ninth centuries identified a novel glassmaking recipe in Cordoba, using lead slag as the main ingredient [ 3 ]. This new glassmaking technology appeared independently of contemporary trends in the Islamic east, but instead bears some resemblance to high lead glass from Carolingian Europe [ 3 ]. Different types of lead glass spread throughout Europe and the Islamic world at more or less the same time, but to what extent these lead glassmaking practices were connected is difficult to tell at present [ 4 – 6 ].…”