The tarnishing of silver in a museum environment is a perennial problem. Silver reacts with atmospheric gases generating a thin disfiguring surface layer. In order to elucidate the nature of the tarnish layer formed in showcase environments in the British Museum,a number of silver. coupons were exposed in different situations inside showcases. SIMS analysis with the Millbrook Chemical Microscope has identified a number of compounds within the tarnish layers. It has indicated a much more complex composition than the silver sulphide commonly associated with silver tarnish. (C) 2002 Elsevier Science B.V. All rights reserved.