Compositions
Glass and other vitreous materials are soda-lime-silicates with significant potash and magnesia. A minimum of three raw ingredients—silica, soda, and a colorant—were used, but other ingredients may also have been added. Textual and archaeological evidence suggests the silica derived from quartzite pebbles, but sand cannot be ruled out. Analysis and written sources show the soda came from the ashes of halophytic (growing in salty soil) desert or coastal plants rather than a purer mineral source such as natron, the natural sodium evaporate used in Roman glass. Lime, which stabilizes the glass and reduces deterioration, may have been added deliberately on its own or incorporated with other raw materials.
A variety of metal colorants was employed: copper for blue, cuprite for red glass, hematite for red faience, lead antimonate for yellow, calcium antimonate for white and opaque blue glass, and sulfur and iron for black and amber glass. Red, black, and amber glass required reducing conditions while white, yellow, and blue glass required oxidizing conditions.
Many studies have compared the compositions of glass from Nuzi and other Mesopotamian sites with contemporary glass from Egypt. Although glass from all these areas is compositionally similar (all being plant-ash soda-lime-silicates), the results indicate systematic and significant differences in the trace element and isotopic compositions because of their slightly different raw materials. An ongoing collaboration between Harvard University, Cranfield University, and London's Natural History Museum is reexamining the glass and related materials from Nuzi; the project is assessing the relationship between the find location and the deterioration of the objects and is developing new models to understand the alteration of soda-lime-silicates during burial.
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