Alchemy and Surface Treatments in Antiquity

Abstract

Ancient artisans were able to confer special colourings to their artefacts by applying particular techniques and treatments, which were lost in later centuries. They were also able to give copper based alloys the appearance of precious metals. Some of these special methods have been discovered and identified on ancient objects. The most famous of these alloys in Roman times was certainly Corinthian bronze, a copper alloy containing small amounts of precious metals, which acquired a purple-black or blue-black patination after a chemical bath. Several ancient texts, in particular Pliny and the alchemists, mention this precious material and give information on how it was produced. However, besides Corinthian bronze there were also other patinated alloys, which imitated the more precious version, and other colouring techniques, which could be achieved in different ways. The present paper reports on the author’s latest research on special alloys in antiquity; several ancient examples of coloured metals and alloys are identified by scientific methods (ICP, AAS, XRD, SEM/EDX), and the problem of recognising the various surface treatments on archaeological objects is discussed.