The Production of Copper–Arsenic Alloys (Arsenic Bronze) by Cosmelting: Modern Experiment, Ancient Practice

Abstract

Cosmelting experiments to produce copper–arsenic alloys were carried out by Lechtman in 1984. The experiments included crucible and furnace smelting techniques utilizing ores collected in the Peruvian Andes. Smelting charges consisted of mixtures of copper oxide ore with either copper sulpharsenide or iron sulpharsenide ore. The experimental furnaces were constructed to resemble furnaces excavated at Batán Grande, a large ore smelting site on the Peruvian north coast where copper–arsenic alloys were produced during the Middle Horizon and later.The cosmelting experiments yielded coherent copper–arsenic alloy ingots over a wide range of oxide: sulpharsenide ore mixtures. Crucible/furnace charges containing ratios of between 2:1 and 4:1 oxide:sulpharsenide mineral produced clean metal, fully separated from slag or matte byproducts. The sulphide ores were not roasted prior to smelting; no flux was added to the charges.Study of the metal ingots, mattes, and slags helps determine the chemical and thermodynamic reactions and the phase separation mechanisms that took place inside the smelting enclosures. The copper–arsenic alloys found in ancient artefacts could have been made easily, deliberately or accidentally, by cosmelting procedures.