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LOOKING AT CHANGES IN TECHNOLOGY OVER TIME: CHEMICAL CHARACTERISATION AND REPRODUCTION OF ISLAMIC GLASS FROM RAQQA, SYRIA*Sean McLoughlin (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. |
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