Where is All the Amalgam Silvering?

Abstract

ABSTRACTAmalgam gilding was one of the most common techniques for the gilding of metalwork before the invention of electroplating. Its silver equivalent, amalgam silvering, was executed in the same manner, by applying a paste of silver amalgam and mercury to a copper alloy object and subsequent heating to form a diffusion bond between substrate and plating and to evaporate the excess mercury, followed by burnishing of the surface. The technical know-how was readily available. However, even though many medieval and post-medieval European metal objects were silver plated, only a few coins and small objects like medieval decorative mounts and horse trappings, and post-medieval astronomic instruments have been reported as examples of amalgam silvering. The technique was also used in China in the 3rd-1st century BC. Should we assume that there are many more amalgam silvered objects waiting to be discovered, as has been suggested? This paper investigates silver plated objects from 3rd century BC Chinese belt hooks to 18th century French decorative art and compares the analytical evidence with original silvering recipes and replication experiments, which showed that with amalgam silvering satisfactory results were far more difficult to achieve than with fire-gilding. It was found that the presence of mercury in XRF analyses of silver plated surfaces did not necessarily identify amalgam silvering, and that some allegedly amalgam silvered objects may in fact have been plated with silver chloride based electrochemical replacement silvering pastes.