precious metal alloys

Precious metal alloys draw from the transition metals of Groups 8 through 11. These include various colors of alloy gold, including yellow gold (gold with copper and silver), white gold (with nickel and sometimes copper and zinc), red gold (with copper predominant over silver), green gold (with silver predominant over copper) and palladium white gold (with palladium). The more exotic gold alloys include gray gold (with cobalt) and blue gold (with iron); there is even a purple gold alloy (with aluminum) Pre-Colombian artisans in South America used "tumbaga", an alloy of gold and copper. Silver alloys include coin silver (with 10% copper), sterling silver (with 7.25% copper) and the Japanese alloy called "shaku-do" (silver with 4% gold). Platinum may be alloyed with gold, although this is now uncommon. More often, platinum is alloyed with palladium or iridium. Rhodium and osmium are also alloying agents for platinum and iridium. Platinum-iridium alloys are used for jewelry and surgical pins. Platinum-rhodium alloys are used for thermocouples. 18K gold solders contain cadmium to lower the melting point of the alloy.