The production of speiss (iron arsenide) during the Early Bronze Age in Iran

In this paper, analyses of some unusual slag samples from the prehistoric site of Tepe Hissar in northeastern Iran are presented. These slags are the remains of a five-thousand-year-old pyrotechnological process that produced speiss, a quasi-metallic material usually formed as an accidental by-product of copper or lead smelting. We argue that the “speiss slags” from Tepe Hissar suggest the intentional production of iron–arsenic alloy (“speiss”) in prehistory. Why the Tepe Hissar metalworkers produced speiss is a question that requires further investigation, but our preliminary assessment suggests that it was to provide arsenic as an alloying component for arsenical copper, the preferred copper alloy during much of the Early Bronze Age in Iran, and widely used across the ancient world. This recognition significantly advances our understanding of the early stages of metallurgy in the Old World.