MICROCHEMICAL INVESTIGATION OF ANCIENT SILVER AND GOLD PLATED OBJECTS: COATING TECHNIQUES AND DEGRADATION MECHANISMS

The manufacturing techniques used in ancient times for coating the copper or silver core of Greek, Roman, Barbarian, Dark and Middle Age artefacts with a thin or thick layer of gold or silver have been studied by means of the combined use of different analytical techniques in order to elucidate some aspects of the manufacturing processes. The results indicate that several methods were used including the simple mechanical application of a thin malleable gold foil or the most complex and sophisticated method based on the use of mercury i.e. the so called fire gilding. The results of the study of golden altar of S. Ambrogio (825 AD) in Milan (Italy) are also presented with the description of the manufacturing processes of this fascinating example of large gilded artefact. Finally, corrosion mechanisms acting during the long-term archaeological burial has been investigated in order to identify degrading agents and mechanisms.