Role of Materials Analysis in the Reconstruction of Early Metal Extraction Technology: Zinc and Silver-Lead Smelting at
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ROLE OF MATERIALS ANALYSIS IN THE RECONSTRUCTION OF EARLY METAL EXTRACTION TECHNOLOGY: ZINC AND SILVER-LEAD SMELTING AT ZAWAR, RAJASTHAN I C FREESTONE*,
A P MIDDLETON*,
P T CRADDOCK*,
L K GURJAR**,
* British Museum Research Laboratory, **
London WClB 3DG Hindustan Zinc Ltd, 6 New Fatehpura, Udaipur 313001,
D R HOOK*
India
ABSTRACT Microscopy and elemental analysis of ore, slag, ceramic and ash from a major metallurgical site have allowed insights into the ancient processes. Constraints have been placed on raw materials and smelting conditions, and aspects of technological change and development have been recognised.
INTRODUCTION Some 30km South of Udaipur, Rajasthan, lies the site of Zawar, which uniquely preserves a key development in the history of metallurgy. Here, the principle of the distillation of metallic zinc appears to have been applied on a large scale for the first time, as long ago as the twelfth century AD, perhaps earlier (1,2 . Zinc boils at around 910 C, which is below the temperature at which its oxide can be reduced by carbon. Unlike the other metals in common use in the pre-industrial world, which could be reduced and separated from unwanted slag as liquids, it was necessary to distill zinc and condense it from the vapour phase. There are occasional finds before the fifteenth century which suggest the incidental, probably accidental, condensation of zinc in the flues of furnaces dedicated to the extraction of other metals such as lead (3]. However, in general, the use of zinc was restricted to brass, which was produced by the cementation process, where zinc oxide was added to metallic copper and reduced directly to the alloy under charcoal. Not only are the remains at Zawar unique but also they are extensive and the preservation is exceptionally good. In addition to the extraction of zinc in the medieval period there is evidence of the extraction of lead and silver, and of the mining of zinc ore for the production of cementation brass, dating well back into the first millennium BC [1,2]. The present paper is concerned in particular with the results of an ongoing programme of investigation of the details of the ancient smelting technologies (4,5].
THE SITE The ancient mining and smelting remains are concentrated in an area of about 6x3km. The topography is steep and reflects the underlying Precambrian geology. Ridges of hard dolomite and quartzite are surrounded by lower hills and valleys of slate and phyllite. The metal ores are principally of sphalerite (ZnS), galena (PbS) and pyrite (FeS 2 ), and they are stratabound in the dolomite. Thus the ancient mines are on the ridges, while the smelting remains occur primarily along the valley of the River Tiri, which runs through the area (Fig.l). The deposits of metallurgical debris take a number of different forms: 1. Deposits of lead-silver smelting slag, which is observed spread on the surface in discrete "sites" up to about 1 hectare in extent.
Mat. Res. Soc. Symp. Proc. Vol. 185. ,'1991 Materials Research Society
618
* Type I slags
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