Tarnishing of silver in environments with sulphur contamination

Abstract

PurposeThis paper seeks to investigate work on silver sulphide formed on the surface of silver metal which was exposed to an environment containing sulphur contamination.Design/methodology/approachLaboratory tests were performed to determine the effect of the surface state, relative humidity, temperature and illumination.FindingsIt was indicated that sulphuration of silver was accelerated by mechanical polishing and illumination. The exposure was performed at 0, 54, 75 per cent relative humidity (rH) and at 16, 25, 37, 47 and 57°C. The tarnish rate at 54 per cent rH was more than two times than that at 0 per cent rH or 75 per cent rH, and the rate increased as a function of temperature.Originality/valueA tarnish model was proposed. The tarnish reaction of silver is chemical reaction controlled, which is in accordance with the result deduced from the model.