This work studies the chemical composition of copper tarnish products formed at 40, 60, and 80% relative humidity (RH) in an uncontaminated environment, for 21 days experimentation at 30°C. The experimental method used was X-ray photoelectron spectroscopy (XPS) in conjunction with -ion sputtering. The main compounds found were cuprite and copper hydroxide Differences were observed between 40, 60, and 80% RH. Copper specimens exposed to 40% RH show the thickest tarnish layers, while the thinnest correspond to the 80% RH specimens. The tarnish layer of the copper specimen exposed to 80% RH is constituted mainly by copper hydroxide. For the 40 and 60% RH copper specimens the tarnish layer is a mixture of copper hydroxide and cuprite. © 2000 The Electrochemical Society. All rights reserved.