Copper smelting slag from the Oberalbstein (Canton of Grisons, Switzerland). Methodological considerations on typology and morphology

Abstract

Mining archaeologists and archaeometallurgists have attempted to decipher the prehistoric multistage process of copper smelting from chalcopyrite for a number of decades. For this purpose, various examinations of archaeological remains, historical and ethnographical comparisons and archaeological experiments have been carried out. Apart from archaeological structures such as furnaces, very little if any of the original raw materials (copper ore) or final products (matte/raw copper) remain from which the process could be reconstructed. Only smelting slag is usually available in vast quantities. By conducting geochemical and mineralogical analyses of this by-product, information can be gained concerning the raw material, charge composition, process temperature, furnace atmosphere and even the resulting (intermediate) product. Despite these efforts, a number of questions remain unsolved, e.g. the much-debated association of different slag types with different process steps or reactors. From an archaeological point of view, this is due in part to the fact that slag samples are usually described and discussed in insufficient detail, if at all. They are often generally classified as one of only two tentatively defined types: “slag cakes” and “plate slags”. This paper aims to demonstrate the additional value of a detailed archaeological evaluation of macroscopic characteristics of smelting slag using finds from the Oberhalbstein region (Canton of Grisons, Switzerland) as an example. The typology and morphology of smelting slag must be taken into account in addition to, and not instead of, further investigations, particularly of geochemical and mineralogical analyses.