Alloys from Anau: The Manipulation of Metallic Properties in 3 rd Millennium B.C. Southern Central Asia
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Alloys from Anau: The Manipulation of Metallic Properties in 3rd Millennium B.C. Southern Central Asia Nathaniel L. Erb-Satullo1 1
Department of Anthropology, Harvard University, Peabody Museum, 11 Divinity Ave., Cambridge, MA 02138 ABSTRACT Metallography, chemical analysis, and microhardness testing of copper-alloy objects from Anau, Turkmenistan (c. 3000-2400 B.C.), were undertaken to determine how technological choices influenced the properties of the finished objects. Additionally, this analytical program assessed the position of the Anau metals in the development of metallurgy in southern Central Asia. Metallographic analysis of three bladed objects, all copper-arsenic alloys with 1% to 5% arsenic, showed that their edges had been cold-worked to a greater or lesser degree to create a blade that maintained a sharp edge, but also had flexibility to withstand impacts. Microhardness testing confirmed that the blade edges had a higher hardness than the interior metal. One of the objects had sulfur-rich inclusions in the metal matrix, suggesting the original charge had at least some sulfide ore. Conversely, a curved rod, made from a copper-lead-tin alloy, was cast to shape and showed no additional working of the metal. Lead, visible as black particles in the microstructure, was likely added to make the molten metal flow more easily. The metallographic and chemical analyses showed that the Anau objects fit into the tradition of Southern Central Asian metallurgy, though the presence of tin in objects of this period is more rare here than in later periods. Anau smiths displayed an ability to manipulate both physical and chemical properties of metal in order to produce functional objects with optimal characteristics. INTRODUCTION Archaeologists have had a long-standing interest in the early development of metal production in human societies, and the ways in which people manipulated metallic properties. Reconstructing the methods by which ancient metal objects were produced not only provides an understanding of the technical abilities of ancient peoples, but can also illuminate how they thought about metal. Past peoples developed divergent methods for dealing with the properties and constraints of metal production, leading Lechtman to develop the concept of “technological style” as a complement to “artistic style.”1 Archaeologists must examine the choices made by ancient metal producers at each stage of production, from the selection and smelting of the ore, to the methods of shaping and the final form of the object. Metallographic examination of polished and etched sections illuminates the choices made during the forming stage of the artifact by reconstructing its thermal history. By combining metallographic analysis with WDS microprobe analyses and microhardness testing, this study reconstructs the technical decisions made in the production of several metal artifacts from Anau, Turkmenistan, during the 3rd millennium B.C. Particular attention was given to the edge treatment of bladed objects, to determine whether they
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