''Tumbaga'' is the name for a non-specific

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile m ...

and copper given by Spanish

Conquistadors Conquistadors (, ) or conquistadores (, ; meaning 'conquerors') were the explorer-soldiers of the Spanish Empire, Spanish and Portuguese Empires of the 15th and 16th centuries. During the Age of Discovery, conquistadors sailed beyond Europe to ...

to metals composed of these elements found in widespread use in

pre-Columbian In the history of the Americas, the pre-Columbian era spans from the original settlement of North and South America in the Upper Paleolithic period through European colonization, which began with Christopher Columbus's voyage of 1492. Usually, t ...

Mesoamerica Mesoamerica is a historical region and cultural area in southern North America and most of Central America. It extends from approximately central Mexico through Belize, Guatemala, El Salvador, Honduras, Nicaragua, and northern Costa Rica. With ...

in North America and South America. The term is believed to be a borrowing from Malay , meaning ' copper' or '

brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...

'. It has also been spelled ''tumbago'' in literature.

Composition and properties

Tumbaga is an alloy composed mostly of gold and copper. It has a significantly lower

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

than

or copper alone. It is harder than copper, but maintains

malleability Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...

after being pounded. Tumbaga can be treated with a simple

acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

, like

citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...

, to dissolve copper off the surface. What remains is a shiny layer of nearly pure gold on top of a harder, more durable copper-gold alloy sheet. This process is referred to as

depletion gilding Depletion gilding is a method for producing a layer of nearly pure gold on an object made of gold alloy by removing the other metals from its surface. It is sometimes referred to as a "surface enrichment" process. Process Most gilding methods are a ...

Use and function

Tumbaga was widely used by the pre-Columbian cultures of South and Central America to make religious objects. Like most gold alloys, tumbaga was versatile and could be cast, drawn, hammered, gilded, soldered, welded, plated, hardened, annealed, polished, engraved, embossed, and inlaid. The proportion of

to copper in artifacts varies widely; items have been found with as much as 97%

while others instead contain 97% copper. Some tumbaga has also been found to be composed of metals besides gold and copper, up to 18% of the total mass of the tumbaga. Tumbaga objects were often made using a combination of the lost wax technique and depletion gilding. An alloy of varying proportions of copper, silver, and gold (typically in a percentage ratio of 80:15:5) was cast. After removal it was burned, turning surface copper into copper oxide, which was then mechanically removed The object was then placed in an oxidizing solution likely composed of sodium chloride (salt) and ferric sulfate. This dissolved the silver from the surface, leaving only gold. When viewed through a microscope, voids appear where the copper and silver had been.

The "Tumbaga" Wreck

In 1992, approximately 200 silver "tumbaga" bars were recovered in wreckage off

Grand Bahama Grand Bahama is the northernmost of the islands of the Bahamas, with the town of West End located east of Palm Beach, Florida. It is the third largest island in the Bahamas island chain of approximately 700 islands and 2,400 cays. The island is ...

Island. They were composed mainly of silver, copper, and gold plundered by the

Spaniards Spaniards, or Spanish people, are a Romance ethnic group native to Spain. Within Spain, there are a number of national and regional ethnic identities that reflect the country's complex history, including a number of different languages, both ...

during the conquests of Cortés and hastily melted into bars of tumbaga for transport across the Atlantic. Such bars were typically melted back into their constituent metals in Spain.

References

External links

Shipwreck recovered right after the conquest of Cortés with tumbaga gold bars

* ttp://libmma.contentdm.oclc.org/cdm/compoundobject/collection/p15324coll10/id/119785/rec/1 The Art of Precolumbian Gold: The Jan Mitchell Collection an exhibition catalog from The Metropolitan Museum of Art (fully available online as PDF), which contains material on Tumbaga {{Jewellery Copper alloys Gold Science and technology in Mesoamerica Precious metal alloys

Composition and properties

Use and function

The "Tumbaga" Wreck

See also

References

External links