Study of environmental degradation of silver surface

To evaluate the evolution of a dark film formation on silver surface objects, several coupons were catalogued and place inside a museum, located in an urban area. The changes on the samples were measured by spectroscopic ellipsometry, in periods of month. This technique allows the reduction of the coupons exposure time, in several months, due to its high sensitivity to surface modifications, with acceptable results for the evaluation of its degradation. The thicknesses of the degradation. The thicknesses of the degradation layers and the optical properties of silver oxide, chloride and sulphide reference samples were determined using a mixture of Tauc-Lorentz and Drude models. The composition of the silver corrosion layer was determined by fitting the layer using a Bruggeman Effective Medium Aproximation (BEMA) of the three depends in the placement of the coupons, namely, inside or outside displayers. The average film thickness after 6 months was of 180 angstrom and 280 angstrom inside and outside the displayers, respectively. The main compounds found in the layers were the silver chlorides and sulphides, which composition changed with the thickness of the layer, and the exposition time.