Gold parting

Gold parting is the separating of gold from silver. Gold and silver are often extracted from the same ores and are chemically similar and therefore hard to separate. Over the centuries special means of separation have been invented.

The very earliest precious metals had mixes of gold and silver; gold and silver alloy is called electrum. With the advent of coinage, methods had to be invented to remove impurities from the gold so that gold of specific purities could be made. Cupellation was able to remove gold and silver from mixtures containing lead and other metals, but silver could not be removed. Gold parting as a process was specifically invented to remove the silver. The main ancient process of gold parting was by salt cementation and there is archaeological evidence of that process from the 6th century BC in Sardis, Lydia. In the post-medieval period parting using antimony, sulfates and mineral acids was also used. In the modern period chlorination using the Miller process, and electrolysis using the Wohlwill process are the most widely used methods of refining gold by removing silver and platinum.

The very earliest attempts at refining gold can be shown by the surface enhancement of gold rings. Gold quality was increased at the surface by 80–95% gold compared to 64–75% gold at the interior found in Nahal Qanah Cave dated to the 4th millennium BC. Further evidence is from three gold chisels from the 3rd Millennium BC royal cemetery at Ur that had a surface of high gold (83%), low silver (9%) and copper (8%) compared with an interior of 45% gold, 10% silver and 45% copper. The surface was compacted and heavily burnished and indicates early use of depletion gilding.

Separation of gold from silver was not practised in antiquity prior to the Lydian Period (12th century BC to 546BC). Material from Sardis (in modern Turkey) is evidence of the earliest use of gold and silver parting in the 6th century. Literary sources and the lack of physical evidence suggest that gold-silver parting was not practised before the mid first millennium BC. Gold parting came with the invention of coinage and there is no evidence for the use of a true refining processes before the introduction of coinage. As refining gold (as opposed to surface enhancement) results in a noticeable loss in material, there would have been little reason to do this before the advent of coinage and the need to have a standard grade of material.

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