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185 Abstract The differentiation of glass-making traditions between primary production centers in the ancient Middle East based upon chemical differences is a difficult process because the complexities of glass manufacture can change the composition of distinctive original raw materials. However, when used in conjunction with the measurement of radiogenic isotopes, chemical analyses can provide an improved assignment of geological provenance for plant ash glasses based upon differences in strontium (Sr) and neodymium (Nd) isotopic ratios. The 87 Sr/86 Sr ratio found within semidesert halophytic plants reflects the relative geological age of the lime present in the soil in which the plants grow, and the 143 Nd/144 Nd ratio in silica also reflects its relative geological age. Each of these ratios is maintained throughout glass production and provides a measure of provenance. The ability of isotopic analysis to characterize glass from a primary production center, and to distinguish it from imported items, is illustrated with a case study on the primary glass-making site of Al-Raqqa, Syria. 1. Introduction: A context for glass provenance; scientific analysis and glass production Man-made glass is a complex and potentially valuable material. In the past it was used in a wide range of ritual, functional, political, and economic contexts. In each ancient period glass production was affected by social, political, and economic factors in different ways. The occurrence of glass in well-defined archaeological contexts provides us with an important basis on which to interpret its use, value, and significance to ancient societies; historical evidence can also provide us with glimpses of how glass was perceived as a material, where it was produced, and how it was used. The scientific analysis of glass offers a different means of investigation. It generates “objective” data that reflect the decisions made by those involved in glass-making. How scientific data can be linked to various social groups involved in the chaîne opéra­ toire for glass production is difficult to assess, but it is nevertheless very worthwhile attempting to create such links. Even if we are unable to provide insights in each (archaeological) case by doing this analysis, the very process should make us focus in a useful way and “stretch” the interpretation of the data as far as possible, creating links between archaeology and science. The use of different scientific techniques to examine glass provides a means of measuring different characteristics of glass and the raw materials used to make it. However, the chemical characteristics of glass raw materials are not necessarily carried through to the glass unaltered. Nevertheless, if at least some of these remain unaltered during the process of glass production, then it becomes possible to build up knowledge about production traditions used, and the information can be applied to provenance the glass. Chapter 14 The Provenance of Ancient Man-made Glass Raw Materials and the Use of Chemical and Isotopic Analytical Techniques Julian Henderson 186 | OBSIDIAN AND GLASS PROVENANCE Glasses produced at different times in different places can have distinctive elemental characteristics . As far back as the mid 19th century, scientists initially using destructive wet-chemical techniques defined compositional characteristics that tied glasses to a particular area or period of production (Turner 1956a; Sayre and Smith 1961). Later, clear distinctions between, for example, Bronze Age plant ash and mixed alkali glasses and between these and (later) Iron Age, Hellenistic, Roman, and Byzantine natron glasses became apparent (Henderson 2000:36–51). Glass with high alumina contents has been found in India, Africa, and the Far East from at least as early as the fourth century BC (Robertshaw et al. 2006; Dussubieux et al. 2008), and occasionally in the Middle East (Boulogne and Henderson 2009). From the fourth century BC (Han dynasty), high-barium glasses were produced in China, and in this same area some of the first high-potassium glasses are found (Gan 2005). Later, in the medieval West, wood ash glasses of a different high-potassium composition are to be found (Sanderson and Hunter 1981; Jackson and Smedley 2004). These are a selection of glasses with diagnostic elemental compositions that relate to different times and, in a general way, to places of production. So these results might be thought of as conferring a provenance on the glasses, but for archaeological scientists attempting to address some of the issues listed above in detail, these basic compositional characteristics provide a starting point. Determining the trace element signatures of glass microsamples, using laser-ablation ICP (inductively coupled plasma) spectroscopy (Gratuze et...

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