Metalworking Influence on the Corrosion Behaviour of Sterling Silver and Silver Plated Copper

Metalworking methods for silver and silver plated copper artefacts may strongly influence their corrosion behaviour. Various surfaces were generated on sterling silver coupons as well as silver plated copper coupons to simulate traditional shaping techniques and surface finishing procedures on historical silver artefacts. Coupons were either polished by hand, by a fabric disc on a polishing machine, or submitted to a hammering process in reference to the as-received state. All samples were subjected to various aging protocols, such as natural aging, a thioacetamide (TAA) gas test (NBN EN ISO 4538:1995) and a Na2S immersion test (NBN EN ISO 8891:1998). The various surface finishing procedures led to marked differences in the tarnishing behaviour which were evaluated by colorimetry, optical microscopy, and scanning electron microscopy.