The Leather Conservation Centre's involvement in the STEP project is to prepare all experimental skins, carry out artificial aging in a deterioration chamber, and undertake physical testing on samples. To prepare the test skins a batch of six calf skins was processed from the wet salted state through to crust tanned leather under controlled conditions. Two different types of vegetable tannins were selected, i.e., sumac (hydrolyzable type) and mimosa (condensed type). The skins were cut in half down the back and one half tanned with sumac, the other with mimosa. The skins were given a light lubrication with a neat's-foot oil emulsion after tannage. A new deterioration chamber was constructed which consists of a Perspex chamber fitted with a revolving carousel to take leather samples. Into the chamber a combination of the following pollutants can be fed: sulfur dioxide, nitrous oxide, nitric oxide, and ozone. The pollutants are mixed in a gas blender and are carried into the chamber by a compressed air system at a flow rate of 20 liters/minute. An ultraviolet light source in the gas line and a quartz window in the chamber will allow for a study of the influence of photochemical reactions on leather deterioration. The duration of the first aging experiment was 12 weeks and samples were removed at three, six, and 12 weeks. Physical tests performed on the samples consisted of tear and tensile strength together with flex tests. The results of the first experimental run are discussed and plans for future work outlined.