Study of Constituents on the Tarnishing Layer of Silver Alloys

Abstract

Ancient silver artifacts become tarnished when they are exposed to sulfides (H2S) containing environments. As a result, a thin blackish layer is formed on the surface. In spite of the chemical composition, the tarnishing layer has the same color. Nowadays, there is a growing focus on research about tarnish in silver alloys, which allow us to understand its corrosion process, and support decision-making in conservation. However, previous works focused more on sterling silver and on the corrosion problems found on artifacts that are exhibited or stored. This paper studied the constituents of the tarnishing layer in the silver alloys, formed in a (NH4)2S solution, by electrochemical cathodic reduction and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Ag2S and Cu2S were identified as the main constituents in this layer. SEM-EDS analysis showed a uniform distribution of Cu on the surface and higher weight loss as the copper content increases in the alloy.