The factors governing the chemical stability of dental casting alloys are not well understood. This is primarily attributed to past reliance on chemistries high in noble metals. Accordingly, the recent surge in use of low nobility alloys has produced concern with tarnish and corrosion. In the proposed research these two variants of alloy deterioration will be studies to establish a battery of objective, quantitative laboratory tests. This test battery will then be used to study both the kinetics and mechanisms of chemical attack. Attention will be focused on determining the effects of alloy nobility, microstructure and test environment. Subsequently the test data will be used to construct a model for alloy deterioration. A critical experimental test of this model (based on environment, microstructure and nobility) will be conducted in the third year. As a consequence of this test program, there will exist both quantitative lab tests and design/selection guides for future and existing low nobility dental casting alloys.