Introduction

Metallurgy plays a significant role in most postNeolithic societies. A number of metals and alloys were known before c. AD 1500, namely gold, copper, lead, silver, tin, iron, and mercury, and the major alloys of bronze (copper-arsenic and copper-tin), brass (copper-zinc), pewter (lead-tin), and steel (iron-carbon). The first origin of many metals was from natural occurrences (‘native metals’), not requiring elaborate smelting or processing, and hence not leaving much waste or slag from their production. Supply of metals increased dramatically with the inception and spread of mining and extractive metallurgy; the geological limitation of metal production to areas rich in specific ores, however, remained. Many civilizations flourished in areas devoid of metal ores, such as the large river valley cultures; others were rich in one metal but not another. Thus, from an early period on metals were traded long distances, both as ingot and as finished artifacts, offering opportunities for provenancing studies (see Metals: Chemical Analysis). The waste materials, in contrast, remained at their production site, giving reliable evidence of production local to the archaeological site.

Metallurgical activity leaves three main types of evidence in the archaeological record: metal objects and waste metal, associated products such as slag, and remains of installations such as furnaces or hearths. Of these, slags are typically the best-preserved, most abundant and most informative, but their study requires scientific analysis and expert interpretation. Even the most fundamental of identifications are not always possible using field methods and visual inspection alone. In extreme cases, true metallurgical slag can be confused with geological or other artificial materials. The differentiation between primary production or smelting and secondary production or reworking is typically given by the wider archaeological context, but cannot be taken for granted. It is often difficult to distinguish between ferrous and nonferrous metallurgy, or primary production versus secondary working. Studying the waste material can give very specific information about metallurgical processes and ore types, production technologies, and scale of production, none of which is available from the study of finished objects. Identifying and understanding these aspects of production is at the core of archaeo-metallurgical analysis of slag. The nature of the material to be studied is best suited for a combination of chemical and mineralogical methods of analysis.