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 11^th–12^th 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.