Radical changes in Islamic glass technology: Evidence for conservatism and experimentation with new glass recipes from early and middle Islamic Raqqa, Syria

The chemical analysis of excavated glass fragments from dated archaeological contexts in Raqqa, Syria, has provided a detailed picture of the chemical compositions of artefacts deriving from eighth to ninth and 11th century glassmaking and glassworking activities. Evidence for primary glass production has been found at three excavated sites, of eighth to ninth, 11th and 12th century dates; the first two are discussed here. The 2 km long industrial complex at al-Raqqa was associated with an urban landscape consisting of two Islamic cities (al-Raqqa and al-Rafika) and a series of palace complexes. The glass fused and worked there was presumably for local as well as for regional consumption. Al-Raqqa currently appears to have produced the earliest well-dated production on record in the Middle East of an Islamic high-magnesia glass based on an alkaline plant ash flux and quartz. An eighth to ninth century late 'Roman'/Byzantine soda-lime recipe of natron and sand begins to be replaced in the eighth to ninth century by a plant ash - quartz Islamic soda-lime composition. By the 11th century, this process was nearly complete. The early Islamic natron glass compositional group from al-Raqqa shows very little spread in values, indicating a repeatedly well-controlled process with the use of chemically homogeneous raw materials. A compositionally more diffuse range of eighth to ninth century plant ash glass compositions have been identified. One is not only distinct from established groups of plant ash and natron glasses, but is believed to be the result of experimentation with new raw material combinations. Compositional analysis of primary production waste including furnace glass (raw glass adhering to furnace brick) shows that contemporary glasses of three distinct plant ash types based on various combinations of plant ash, quartz and sand were being made in al-Raqqa during the late eighth to ninth centuries. This is a uniquely wide compositional range from an ancient glass production site, offering new insights into the complexity of Islamic glass technology at a time of change and innovation.