1 INTRODUCTION The silver objects exposed in museums and collections are usually coins, jewelry, cutlery, and other decoration objects. During their exhibition, the surface of the silver artifacts could react with gaseous sulphur compounds such as hydrogen sulphide (H 2 S), carbonyl sulphide (OCS) and other organic sulphur compounds forming a dark layer of silver sulphide (Reaction 1 and 2) (Selwyn, 1990, Graedel, 1992). This process is called tarnishing, and the layer formed is not desirable because it produces the alteration of the surface and the loss of the shine, characteris- tic of the silver. 2Ag + H 2 S + ½ O 2 → Ag 2 S + H 2 O (1) 2Ag + OCS→ Ag 2 S + CO (2) The ideal cleaning treatment for silver is one that removes the tarnished layer and modifies the underlying silver surface as little as possible. There are several methods for cleaning tar- nished silver; most of them are mechanical, chemical and electrochemical. According to a sur- vey carried out with worldwide conservators, the most used cleaning methods are mechanical treatments (52%), instead of chemical (37%), electrochemical (10%) or other methods (1%). Conservators frequently use commercial products (~30% of the total), especially for mechani- cal and chemical cleanings. These commercial products could be liquids, foams, pastes, wad- dings or cloths and they are usually made with an inorganic phase identified as the abrasive (SiO 2 , Al 2 O 3 , TiO 2 , CaCO 3 …) over an organic substance (surfactants, soaps, fatty acid…) (Wharton et al., 1990, Selwyn and Costain, 1991). The principal problem with the commercial products is that the composition is unknown and the manufacturer can modify it without inform to consumers, changing therefore their aggressiveness and effectiveness. Impact assessment of different cleaning methods for tarnished silver artefacts T. Palomar, B. Ramírez Barat, D. Lafuente, E. Cano Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC) Madrid, Spain S. Díaz, E. García Instituto del Patrimonio Cultural de España (IPCE), Madrid, Spain ABSTRACT: Different mechanical, electrochemical and chemical methods have been used for many years to remove sulphur tarnishing from silver artefacts. To evaluate the effects of these methods on the metal, silver coupons have been subjected to 6 cycles of tarnishing and cleaning. The cleaning methods evaluated have been mechanical (soft abrasives and polishing); electrochemical (potentiostatic reductions) and chemical (chelating and acid solutions). The abrasives left a smooth surface, since the chemical and the electrochemical methods left a rough texture. The thiourea-acid solutions removed a similar percentage of silver than mechani- cal methods, while the mass of silver cleaned with electrochemical treatments remained con- stant. The thiourea-acid solutions and the potentiostatic reductions were the most effective tar- nishing cleaning methods; although the samples cleaned by a potentiostatic reduction presented a yellowish color and the residues from thiourea acid solution can act as points of re-tarnishing.