EMF - Current Meeting (abstracts)

May 21, 2001

May 2001


*Sean McLoughlin (Department of Materials, Imperial College)
Nargis Al-Sadiq (Department of Materials, Imperial College)
Julian Henderson (Department of Archaeology, University of Nottingham)
David McPhail (Department of Materials, Imperial College)

This presentation is the result of preliminary technical research into glass and related materials from archaeological excavations in ar-Raqqa, situated in the Euphrates valley in northern Syria. Raqqa is the site of a large-scale Islamic industrial complex, active between the 8th and 12th centuries AD, where glass was both fused from its raw ingredients and worked into finished objects.

A collaboration between the Materials Department of Imperial College and the Archaeology Department of Nottingham University, the main focus of this EPSRC funded project lies in applying a range of analytical techniques to a range of materials unearthed at Raqqa that are associated to ancient glassmaking. Information from analytical studies of glassmaking debris can shed light, amongst other things, on ancient glass properties, furnace conditions and operating temperatures, and the raw materials and fuel types used.

Electron probe micro-analysis (EPMA) results on glass compositions from Raqqa concur with the general compositional shift observed between 8th-9th century 'Late Roman' and 11th-12th century Early Islamic glass types. These two glass types at Raqqa are labelled type 3 and type 1, respectively. It is generally accepted that such a shift took place across the Islamic world with a contemporary though different change throughout Europe.

The compositional change is thought to result from the use of different raw materials; quartz replaces sand as the silica source and organic plant ash is favoured as a flux over the evaporite mineral natron.

Work on replica type 3 and type 1 compositions undertaken at Imperial College has shown marked differences in the glass types' physical properties, appreciable in terms of castability, viscosity, fining behaviour and actual working temperatures. The higher alumina and lower magnesia content of type 3 glasses makes them more viscous than type 1. Glasses of higher viscosity require higher temperatures for casting or working and longer fining times for production. A noticeable difference in viscosity and fining time between the two glass types would have had implications on processing parameters and fuel economy.
There is thus reason to believe that the change in composition and the corresponding change in raw materials could have been based, amongst other factors, on practical technological considerations associated with glassmaking.

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