Tumbaga

Subcategory: Copper Alloy; Precious Metal; Nonferrous Metal; Gold Alloy

Key Words: tepuzque, guanine

Material Notes:
Tumbaga is an alloy of gold and copper (and sometimes silver). Gold melts at 1064°C (1947°F) and copper at 1083°C (1981°F). Alloying gold with 15-40% copper gives a metal that melts at 860°C (1580°F). 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. 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 when bellows or men’s lungs produced the furnace draught. 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.