Decisions set in slag: the human factor in African iron smelting

Abstract

Slags are the most abundant and best-preserved product of traditional iron smelting and are thus a staple of archaeometallurgical research in this area. A wealth of technical information has been gleaned from these studies, identifying the bloomery process as the universal method of pre-industrial iron production across the Old World. Despite covering such a vast expanse of land and spanning more than two millennia, there is little fundamental variability in the resulting products – bloomery iron and fayalitic slag. This is at odds with the numerous ethnohistorical studies of traditional iron smelting, particularly in Africa, that have documented a bewildering array of practices, both social and technical. This is most spectacularly obvious from the range of furnace designs, from a mere hole in the ground to elaborately decorated and substantial structures kept in semi- permanent use. The social status of smelters within their societies, or associated ritualised practices, are other examples of wide-ranging diversity in iron smelting. Such diversity is not restricted to Africa, but is matched by a similarly wide range of archaeologically documented furnace designs across prehistoric western Asia and Europe. This paper attempts to chart some common ground among the extremes of technical engineering studies, ethnographic documentation and sociopolitical contextualisation in African iron smelting. First by exploring the inherent factors providing the envelope or constraints of technical possibilities, and then identifying degrees of freedom within this envelope which offer room for, or rather require, human decision-taking. Some of these decisions have left their traces in the slag, and teasing out these variables may eventually offer insights into social and cultural practices through technical studies