A 6000-year-old amulet discovered at a Neolithic site in Mehragarh, Baluchistan province central Pakistan might be the world’s oldest example of applying lost-wax casting technique to create metal objects.
The archaeologists that studied the artefact are sure that this wheel-shaped amulet cannot result from casting in a permanent mould as this shape could not have been withdrawn without breaking the mould – no plane intercepts jointly the equatorial symmetry planes of the support ring and of the spokes without inducing an undercut. The artefact was therefore cast using a lost-wax process.
The artefact was analysed as part of a new study using a technique known as High spatial dynamics photoluminescence imaging in order to determine exactly how it was made. As different materials reflect different amounts of light, this enabled researchers to pinpoint the exact materials used to make the amulet.
The analysis revealed that the amulet was cast as a single piece, leading the researchers to conclude that it was made used a process known as lost-wax casting, which involves creating a replica of the original object using wax, and then creating a mold around it. This is then heated up, the liquid wax poured out and molten metal poured in and once it cools down, the mold is broken apart, leaving the newly formed metal object intact.
The new analysis revealed that the amulet was made by pouring very pure copper melt into a pre-prepared clay mould using lost-wax casting. The copper absorbed a small amount of oxygen during the processing which explains the presence of microscopic copper oxide “bristles” inside the amulet.
(after Nature, Daily Mail, D. Bagault, B. Mille, T. Severin-Fabiani, M. Thoury, L. Bertrand)