Tarnish and corrosion of noble metal alloys.

A factorially designed experiment was chosen to form alloys of a gold-palladium-silver-copper quaternary system. A total of 81 alloys for three levels of concentration of each of the four elements were made and tested for the degree of tarnish in in vivo and in vitro environments. The following conclusions may be drawn: 1. In both the in vitro and in vivo experiments, increasing the gold levels of concentration within an alloy decreased the degree of tarnish. 2. In both the in vitro and in vivo experiments, increasing the palladium levels of concentration within an alloy decreased the degree of tarnish with an influence greater than that produced by the gold content. 3. In the in vitro environment of 2% sodium sulfide solution, the degree of tarnish increased as the levels of concentration of silver to copper were increased. 4. In both the in vitro and in vivo experiments, the effect of the interaction of the four elements on the degree of tarnish and corrosion is directly related not only to the concentration of each element within the alloy, but also to their ratios.