Plant-ash glass in Natronland: A review of the use of plant-based fluxes in glassmaking from the 1st to the 9th century CE in Europe and the Mediterranean basin

This article examines available evidence for the use of plant ashes in glassmaking in the Mediterranean basin and Europe from the 1st to the 8th-9th century CE. During this period, glassmaking in these regions was overwhelmingly dominated by mineral fluxes, primarily natron, but the chemical composition of some glasses found in secure archaeological contexts suggests the use of plant ashes in these glasses, which are, on the other hand, compositionally distinct from glass made in regions where plant ash was used as the standard flux, for instance east of the Euphrates. The chemical characteristics of these glasses are examined, and different criteria are presented to aid in their identification. The chemical features are also interrogated to suggest possible silica and alkali sources and to determine possible similarities and differences in raw materials supply vis-à-vis natron glass. The archaeological and chemical evidence is brought together to try to define the technological, economic, and institutional implications of a possible glassmaking industry using plant ash, whose production parameters differ from those mobilised by the natron glass industry, in the periphery of the Roman world. • Glass with plant ash (IPAN) was made in Natronland throughout the Early Imperial, Late Roman and Late Antique periods. • These glasses coexisted with Natron glass in various ways during this period. • Production of IPAN glass appears to be a recognisable technology throughout this period. • IPAN glass was likely made in small production units, unlike the period's natron glass.