Experimental Reconstruction of the Casting of Copper `Oxhide' Ingots

Article excerpt

One of the most crucial elements in the dynamics of the Late Bronze Age metals trade in the Mediterranean was the production and exchange of copper `oxhide' ingots (Knapp & Cherry 1994). These are basically flat, oblong slabs of nearly pure and unalloyed copper that weigh between 10 and 40 kg. The majority has an average weight of c. 29-30 kg however, and as a result this `standard' has been traditionally equated with the existence of a `talent'. They furthermore form a prominent part of the bulk cargo in shipwrecks discovered at Ulu Burun and Cape Gelidonya (Gale 1991). The results of an extensive programme of lead-isotope analyses aimed at determining the provenance of these ingots have led some archaeologists to propose that most of the ingots were produced from the rich copper resources on the island of Cyprus. Based on the same results, the Oxford group has also discussed the possibility of a specialized centre for their production in the Skouriotissa region of the island (Stos-Gale et al. 1997).

The adoption by Cypriot smiths of their method of production still requires explanation, not least because the earliest dated examples of what most people think of as a typical Cypriot product came from LMI or 16th-century BC contexts on Crete such as Zakro and Aghia Triadha. According to lead-isotope analyses, these pieces do not seem to be compatible with Cypriot ore-types, making a Cypriot origin of this technology highly unlikely. Moreover, they antedate the first evidence of such ingots on Cyprus by some two centuries. In addition, the only known mould for casting such ingots is a stone example from Ras Ibn Hani on the north coast of Syria. On the other hand, the possibility that the `oxhide' ingots discovered in Sardinia might have a terminus ante quem as late as 1100 BC, well after the last piece in Cyprus became deposited around 1150 BC, has naturally generated interest in the economic organization of such a technology at the end of the LBA in the eastern Mediterranean (Gale 1991).

Until recently, archaeologists and archaeometallurgists seemed to underestimate the value of experimentally reconstructing the production processes required to manufacture such large pieces of relatively pure copper. Experimental work can not only shed light on possible trade mechanisms in the 2nd-millennium BC Mediterranean, but far more importantly, it can provide us with organizational models based on the actual technology involved.

The fundamental questions remaining to be answered are the reasons for and possibilities of the transfer of such technological knowledge. In our opinion, this can only be done at this stage by establishing the technological parameters involved in the manufacture of these ingots. By adopting this approach, discussions about the provenance and trade of these ingots will at least be provided with a framework for the actual metallurgical practices of the LBA.

Based on relevant ethnographic analogies (Herbert 1984), archaeological remains at LBA Cypriot sites and earlier experiments by Dr John Merkel (1986), the reconstructions have been designed to test the use of mould materials and surface markings as well as metallographic structures. In particular, the aims are to test the efficacy of sand-formed rather than stone moulds, to evaluate the probability of portable tool-kits and to explain the lack of excavated mould remains on the island.

The negative imprint of an ingot shape in the sand is made by impressing a wooden pattern or by incising the shape with simple tools. …