Glass production for the Silk Road? Provenance and trade of islamic glasses using isotopic and chemical analyses in a geological context

Abstract We report the first Nd and Sr results for sands from inland locations in the Middle East and new Nd and Sr results for coastal sand on the Syro-Palestinian coast. When the isotopic results for Belus sands are combined with our seven new sand samples from the Lebanon we have established the likely range of isotopic signatures for Levantine sand that was used for the manufacture of Hellenistic, Roman, Byzantine and some Islamic glass in the area. The combined isotopic results for sands and Sr results for plants growing in Syria and the Lebanon provides an environmental base-line which has allowed us to identify 5 separate isotopic production zones. We have made direct comparisons with Nd and Sr signatures for raw furnace glasses from al-Raqqa (Syria) and Tyre (the Lebanon), secondary furnace glasses from Banias (Israel) and with new results for four raw glass fragments from the early 11th century CE Serce Limani shipwreck excavated off the coast of Turkey. We have also compared the base line isotopic data with our new isotopic data for twenty one 9th-14th CE Islamic plant ash glass vessel fragments from Damascus and Beirut, and with published isotopic data for al-Raqqa vessel glass. For the first time we have been able to provide a more secure provenance for the late 11th century CE Serce Limani raw glass. It was made from Levantine coastal sand, or an equivalent source of geologically young sand, and has a Sr signature that suggests a production provenance in the Palestinian area, but not in established centres such as Tyre as has been suggested. We are able to suggest an inland isotopic provenance for 9th-12th century Islamic vessel fragments from al-Raqqa, Beirut and Damascus which probably coincides with an area in or near Damascus. Two al-Raqqa vessel glasses with elevated potassium oxide levels and distinctive Nd and Sr signatures may have a central Asian origin. This environmental approach involving isotopic analysis of sands and plants has provided a more sensitive way of provenancing Islamic plant ash glasses found in the Syro-Palestinian area and in Turkey than the use of trace elements has thus far. The five separate production centres/zones we have defined have provided more evidence for a decentralised system of Islamic plant ash glass production, also found across extensive areas of the Silk Road, at least as far as northern Iran.