High alumina plant ash (v-Na-Al) glass bangles from Siraf: Clarifications on a Central Asian glass group (9th-14th century)

During the excavations of 1966–1973 vast quantities of glass were found at Siraf in Iran on the Persian Gulf, primarily dating to the 9th-11th centuries. Some of this glass assemblage held in the Corning Museum of Glass was analysed using LA-ICP-MS, including nine glass bangle fragments dating to ca. 14th century. One was found to be of a high alumina plant ash (v-Na-Al) composition, as was a 14th-15th century glass kohl stick fragment. Further analysis of the 14th-century Siraf glass bangle collection held at the British Museum has now been analysed using LA-ICP-MS, identifying several more v-Na-Al glass bangles. Recent studies have concluded that plant ash soda glasses of Central Asian origin can most notably be characterised by elevated levels of alumina (>4.5 wt%). This article reviews their glass characteristics in the context of a recently improved understanding of glass dating between the 9th-14th centuries from the historic Greater Khurasan region and particularly the v-Na-Al glass collections of Central Asia. This investigation proposes there were at least three main Central Asian glass production groups (CA1, CA2 and CA3) in circulation during this period. These differ primarily on their alumina, titanium and zirconium concentrations. Additional comparison with other relevant glass bangle collections, and v-Na-Al glass recently reviewed from south and east Africa, reveals that multiple chronologically definable subtypes of these groups may have been in circulation. Further to this, while the CA3 category remained relatively local, the CA2 type appears to have enjoyed the widest circulation along caravan routes, yet the CA1 type the widest via maritime routes. These insights offer additional information on the major characteristics of this elusive category of glass, its periods of production and an improved understanding of distribution patterns.