''Tumbaga'' is the name given by Spanish

Conquistadors Conquistadors (, ) or conquistadores (; ; ) were Spanish Empire, Spanish and Portuguese Empire, Portuguese colonizers who explored, traded with and colonized parts of the Americas, Africa, Oceania and Asia during the Age of Discovery. Sailing ...

for a non-specific

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

and

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

, and metals composed of these elements. Pieces made of tumbaga were widely found in

pre-Columbian In the history of the Americas, the pre-Columbian era, also known as the pre-contact era, or as the pre-Cabraline era specifically in Brazil, spans from the initial peopling of the Americas in the Upper Paleolithic to the onset of European col ...

Mesoamerica Mesoamerica is a historical region and cultural area that begins in the southern part of North America and extends to the Pacific coast of Central America, thus comprising the lands of central and southern Mexico, all of Belize, Guatemala, El S ...

in North America and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. The term is a borrowing from the Tagalog ''tumbaga''. This came from Malay , meaning '

' or '

brass Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

'. 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 of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

than

alone . It is harder than

, but maintains

malleability Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...

after being pounded. Tumbaga can be treated with a

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

, such as

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...

, 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.

Use and function

Tumbaga was widely used by the pre-Columbian cultures of Central and South America to make religious objects, as they considered gold a sacred metal. 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

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

while others contain 97%

. 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. It was burned after removal, turning surface copper into copper oxide, which was mechanically removed. The object was 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. It is the third largest island in the Bahamas island chain of approximately 700 islands and 2,400 cays. The island is roughly in area and approximately long west to east and at it ...

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

Spaniards Spaniards, or Spanish people, are a Romance-speaking ethnic group native to the Iberian Peninsula, primarily associated with the modern nation-state of Spain. Genetically and ethnolinguistically, Spaniards belong to the broader Southern a ...

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 compounds Science and technology in Mesoamerica Precious metal alloys

Composition and properties

Use and function

The "Tumbaga" Wreck

See also

References

External links