||Tumbaga is an alloy of gold and copper (and sometimes silver). It ranged in content from 3-97% copper with a balance of gold and several trace metals as impurities; silver could be an impurity or a deliberate alloying element up to 18%. One of the reasons that the composition varies so widely is that it was also the name of the metal bars that were hastily produced from South American raw materials during the early years of European conquest and settlement. These bars were shipped back to Spain and separated back into pure copper, gold, and silver.
The Pre-Hispanic American metal smiths used tumbaga extensively. Alloying gold with 15-40% copper gives a metal that melts at 860°C (1580°F). The alloy is significantly harder than copper, but is malleable like gold and can be hammered. It is therefore ideally suited to the formation of elaborate objects made of hammered sheet metal. Its relatively low melting point was a big advantage to early metal workers. The alloy could be made to look like pure gold by treating the finished face with an acid solution to dissolve the copper and then hammering or polishing to join the gold, creating a uniform gold surface.