Metallurgical analysis of copper artifacts from Cahokia

Copper artifacts from Cahokia Mounds, Illinois were analyzed from a materials science perspective to shed light on techniques used by Mississippian copper workers to deform nuggets of native copper into thin sheets. Eight small copper pieces from a copper-working site at Cahokia’s Mound 34 were subjected to metallographic examination. Replication experiments thereafter recreated features of the artifacts under controlled conditions. It is concluded that copper sheets were thinned through repeated cycles of hammering and annealing performed at temperatures achievable in an open wood fire. The welding of sheets to create multilayered objects was not observed in any artifacts and could not be accomplished experimentally. Additionally, a possible cutting method used on some artifacts was identified.

► Copper sheet artifacts from Cahokia Mounds were metallurgically examined. ► Replication experiments were performed to compare with the artifacts. ► Artifacts were found to have been thinned by repeated hammering and annealing. ► Several artifacts were apparently cut using fatigue bending methods. ► Lamination was not observed and was likely not possible with period technology.