About 1200 years ago, ancient architects in the city of Samarra in the Near East built聽spectacular glass palaces 鈥� the .聽Now, chemists have discovered what the glasses contained, what made them translucent and how they differed from most pre-existing glasses available in the ancient world.
鈥淭hey produced a colourless glass free of coloured taints simply by using a very clean silica source, which makes this group of glasses exceptional for the time,鈥� says Nadine Schibille of the University of Orl茅ans in France.
She and her colleagues analysed 265 glass objects excavated or collected from Samarra, which lies 125 kilometres north of Baghdad in Iraq. Between AD 836 and 892 it served as the seat of the , the third to rule the Islamic world following the death of the prophet Mohammed in 632. Samarra was the birthplace of a 鈥済olden age鈥� of Islam that saw science, medicine, art and intellectual thought flourish until a Mongol invasion in 1258.
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Half the relics comprised everyday glass objects including bowls, plates, bottles, jugs and lamps. The rest consisted of fragments of 鈥渁rchitectural鈥� glass聽that was incorporated into the fabric of buildings 鈥� including Samarra鈥檚 large palaces 鈥� as windows, floors and inlays.聽A lot of the glass was excavated by a German mission a century ago. It was made available to聽Schibille鈥檚 team by the British Museum and the Victoria and Albert Museum聽鈥� both in London聽鈥� and by Berlin鈥檚 Museum of Islamic Art.
For the analysis, Schibille鈥檚 team removed tiny fragments from each artefact, set them in a resin, polished them to remove any contamination then put them聽in a聽mass spectrometer to reveal their chemical fingerprint.
Locally made
In antiquity, most ancient glass聽was made and supplied by the Romans, or by skilled glassmakers living in Egypt and on the Eastern Mediterranean Levantine coast. These glassmakers mixed silicate-rich sand with natron, a form of hydrated soda ash, and melted the two together for several weeks to make molten glass. The natron lowered the melting temperature.
Many of the objects excavated at Samarra were made in this way, and had probably been imported from Egypt and the Levant. But the architectural glass was different. The natron had been replaced with soda-rich ash from burnt plants. At 3.5 per cent by weight, these architectural glasses contained up to three times the amount of magnesium oxide found in the 鈥渘atron鈥� glasses.
This signature was so common to samples of architectural glass, and so distinct from the natron-based glasses, that Schibille鈥檚 team concluded that the architectural glasses must have been custom-made locally and in amounts large enough to adorn Samarra鈥檚聽lavish palaces. They say there is support for this idea from ancient scripts: a nearby town called al-Qadisiyya was described in the thirteenth century as the 鈥淕lassworks鈥�.
鈥淭hese results are an important contribution to our understanding of the development of the Islamic glass industry, and the later, high-quality glasses of the Renaissance which employed a similar technology,鈥� says Ian Freestone of University College London.
PLoS One
