The soft alloy has been, in some circumstances, found to contain as much as 97% copper, while in others, as much as 97% gold, and was primarily used in the design of religious items.
One reason for the metal's popularity was its ability to form an eutectic alloy - that is an alloy that melts at a lower temperature then any of its constituent metals. A mixture of 70 percent gold and 30 percent copper melts at about 1472ºF (800ºC).
The greatest collection of tumbaga metal still in existence was salvaged from a Spanish shipwreck of the coast of Great Bahama Island in 1992. Over 200 bars of the alloy, plundered from the Aztecs and Incas, were en route to Europe when the ship went down ca. 1528. Although tumbaga was not produced in bars, the Spanish would melt precious metals into ingots for transport across the Atlantic.
Image: A tumbaga ingot recovered from the Henry VIII wreck. Source: Marex Global Deep Sea Recovery.