Blue and purple gold alloys have been recognized for a long time. They form in alloying systems that combine gold with gallium/indium and aluminum, respectively. The alloys, however, are known to be very brittle and possess low corrosion resistance. Taking into account these negative aspects, this paper describes the results of a European-funded research project. Surface engineering techniques and investment casting were used for manufacturing jewelry items with selectively coated colored surface. Coatings of AuGa2 and AuIn2 blue gold alloys were applied on 18K gold, sterling silver and 950 Pt jewelry by electroplating, laser/torch cladding or dipping into liquid gallium. The properties of the blue and purple gold alloys and coatings, such as corrosion resistance, metal release rates, hardness and color, and the influence of alloying additions on these properties are presented and discussed. The suitability of blue gold coatings for jewelry purposes will be discussed in the light of reliability and feasibility.

Author: Dr. Ulrich E. Klotz