PURPOSE: To form a hard black carbide film on the surface of a worked product by blending elements, such as B, with a specific gold alloy in a specific ratio to produced a worked product and then applying carburizing treatment to the above worked product under specific conditions by the use of a solid carburizer, etc.
CONSTITUTION: A gold alloy which consists of, by weight, 99.9-55% of pure gold, Au-Ag alloy containing ≤40% silver, of Au-Ni alloy containing ≤40% Ni and 0.1-45% of one or ≥2 elements among B, Si, Fe, Co, T1, Nb, and Mo is refined and cast into a worked product. This worked product is surface- treated and then subjected to carburizing treatment at a temp. of the melting point of this gold alloy or below for ≥10min by using a gaseous mixture consisting of hydrogen, carbon oxide, and hydrocarbon and a solid carburizer composed of a powder mixture prepared by adding Na2CO3 and BaCO3 to powdered charcoal or coke fires, by which a film of the hard black carbide of the additive element is formed on the surface of the worked product, followed by butting. By this method, the blackened gold alloy hitherto impossible to obtain can be manufactured.
MORITA NOBORU
SEKINAKA TADASHI
OKIMORI YUTAKA
YOSHIDA KYASUTO KOGYO KK
KAWASAKI YONEKICHI
SEKI KK