Charles C. Kolb Award - Catherine Klesner

Investigation of provenances of early Islamic lead glaze from northern Central Asia using elemental and lead isotope analyses

Catherine Klesner, New York University

This paper presents the results of the compositional and lead isotopic characterization of a representative collection of Early Islamic glazed ceramics from eleven medieval sites in the Semirechye region and adjacent river valleys (Syr Darya, Talas, and Chu).  This region, which lies along the northern edge of the Tianshan mountains in modern-day southern Kazakhstan and northern Kyrgyzstan, has served as an avenue for long distance trade for millennia. In the 6th c. CE, trade intensified over this northern branch of the Silk Road and the following six centuries were a period of political, economic, and cultural change. Archaeological sites from this time provide valuable insights into this trade as well as the economies and technologies of the supporting communities. By examining the material remains from these sites, it is possible to reconstruct both ancient trade networks, as well as the technological and knowledge networks that were facilitated by the increased interactions occurring along these paths. The paper is part of a larger study of glazed ceramics from Central Asia which investigating the scale of local production and long-distance trade of ceramics from the 9-15th c. CE, the extent of local technological innovations, and the identification of raw materials used by local craftspeople to produce the glazed wares. Through the examination of ceramic provenance and technological analysis of local and nonlocal ceramics, we can better understand both the physical trade networks in place in northern Central Asia during the 9th -15th c., but also how technologies were transmitted and adapted.

The ceramics were examined by LA-ICP-MS and EMPA to determine the chemical composition and microstructure which informed us about the glaze type, colorants, and opacifiers used by local craftsmen. Several distinct glaze types are present including transparent high-lead glaze (n=66) and opaque high-lead glaze (n=10), of which tin-opacified glazes, tin- and antimony-opacified glazes, and antimony-opacified glazes were all identified (see figure 1). The occurrence of antimony-opacified glazes, and tin- and antimony-opacified glazes is unattested in this region in the Early Islamic Period and indicates that the local craftsmen in southern Kazakhstan are innovating in their production of opaque glazed ceramics using local raw materials.

Lead isotope analysis was employed to identify potential sources of lead, and the results indicate that the craftsmen were obtaining lead from at least two different sources for their glazed production. Using a large comparative database and through the application of Euclidean distance, we were able to identify potential ore deposits from the Central Asian Orogenic Belt (see figure 2), including deposits that were active silver mines during the Medieval Period. These ore sources were local and suggest that potters were obtaining lead for glaze production from within larger acquisition networks. High levels of bismuth identified in the glazes, which is characteristic of silver from the Tianshan mountains, reinforces the conclusion that the lead was source from silver mines. The high levels of bismuth also could suggest the use of litharge from silver cupellation as the raw material for the lead glazes, the results of this initial characterization suggest a link between silver metallurgy and ceramic production in the Early Islamic Period.One cluster of samples (n=8) had a distinct isotopic signature that matched a unique deposit in Xinjiang, China, which indicates craftsmen were not strictly using local sources, but also obtaining lead through long-distance trade networks.