Calcolithic Coppers of Peru

Abstract

The present work describes the origin and description through metallographic characterization of different objects: tools and weapons found in an archeological deposits in Batán Grande near Piura in Peru. The comprehensive available literature reviewed indicates that the base metal was reduced at low temperature with charcoal, starting from oxidized indigenous ores to which later, during its processing, other ores of an arsenical nature coming from distant places were added. The ore deposit was named Huaca after the burial of some principal local character of the time. This Huaca deposit has been chronologically assigned to the Calcolithic Age, before the American Bronze Age. The copper alloys found were of the arsenical type. These alloys could be melted and cast at low temperature because of the attractive effect of arsenic additions to copper. Arsenic also plays an important role in the solid-solution strengthening of copper, although, to some extent, it impairs other desired mechanical properties, such as toughness. The as-cast preforms were further strengthen by work hardening during cold deformation operations to sharpen cutting edges and other thin sections. The alloys of low As content normally had sufficient toughness. The use of these primitive copper alloys overlaps in time with those in the American Bronze Age (1000 a.d.), producing cleaner and, therefore, better artifacts through their more advanced processing techniques.