Abstract
The objective of this study was to develop a casting investment that prevents the blackening of the cast surface of noble metal alloys. Experimental investments were prepared using a gypsum-bonded investment in which a hydroxide, namely Mg(OH)2 or Ca(OH)2, was added. An Ag-Pd-Cu-Au alloy was cast into the mold made of the prepared investment. The addition of both hydroxides showed a significant effect on the color of as-cast surfaces, which was improved with increase in additive content. When Mg(OH)2 or Ca(OH)2 was added at more than 4.0 mass% to the investment, it was useful in preventing the blackening of the as-cast surfaces of an Ag-Pd-Cu-Au alloy. As for differences in the effects between Mg(OH)2 and Ca(OH)2, they were not found.
