Reconstitution of the stages of the metallurgical process used to produce the Mehrgarh amulet

Reconstitution of the stages of the metallurgical process used to produce the Mehrgarh amulet, a copper object from the ancient Chalcolithic period found in the 1980s in present-day Pakistan. The secret of its manufacture has been revealed thanks to a new approach using UV/visible photoluminescence spectral imaging. A model was formed in a ductile material with a low melting point such as beeswax. Different wax coils were melted to each other by lightly heating their ends. The wax model was then encased in clay to form a mould. The mould was first heated to run off the melted wax, then fired at a high temperature. Molten copper was then poured into the mould to fill space previously occupied by the wax model. After cooling the mould was broken to remove the copper object. Abandoned on the ground, the copper slowly corroded completely, forming hydroxychlorures in the dendrites (green) and cuprous oxide in the interdendritic area (red).