Arsenic Bronze: Dirty Copper or Chosen Alloy? A View from the Americas

Abstract

This article is dedicated to Ronald F. TylecoteArchaeologists and historians of metallurgy have attempted to explain the gradual abandonment of arsenic bronze in favor of tin bronze in the ancient Old world by making comparisons between the mechanical properties of the two bronzes. These comparisons purport to show the superiority of copper-tin alloys over alloys of copper and arsenic, despite an absence of data on the physical properties of the copper-arsenic system. The study reported here presents the results of mechanical tests carried out on experimental samples of both types of bronze over a broad range of alloy compositions. Hardness, tensile strength, and elongation determinations were made on cold worked and hot worked (forged) material. Whereas tin bronzes can be work hardened more extensively than arsenic bronzes, the far greater ductility of arsenic bronze makes it a desirable alloy for the manufacture of thin metal sheet. The widespread use of low-arsenic copper-arsenic alloys in the Americas, especially in the Andean culture area, is attributable in part to the tradition there of sheet metal production in the elaboration of three-dimensional forms.