Tumbaga
Encyclopedia
Tumbaga was the name given by Spaniards to a non-specific alloy
of gold
and copper
which they found in widespread use in pre-Columbian
Mesoamerica
and South America
.
than gold
or copper
alone. It is harder than copper
, but maintains malleability after being pounded.
Tumbaga can be treated with a simple acid
, like citric acid
, 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
.
The proportion of gold
to copper
in artifacts varies widely; items have been found with as much as 97% gold
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 the lost wax technique and the alloy used was a mixture of copper (80%), silver (15%), and gold (5%). The indicated concentrations varied from object to object. Once the object was taken out of the cast, it was burned and as a consequence, copper from the surface of the object was oxidized to copper oxide and was then removed mechanically. The object was then placed in an oxidizing solution containing, it is believed, sodium chloride (salt), and ferric sulfate. This process removed through oxidation the silver from the surface of the object leaving only gold. When looking through a microscope, one may clearly see the empty spots from where the original elements copper and silver were removed.
Island. They were composed of mainly silver, copper, and gold plundered by the Spaniards during the conquests of Cortés
and hastily melted into bars of tumbaga for transport across the Atlantic. Because all the metals that reached Europe were melted back into their constituent metals in Spain, the bars found in the shipwreck are the only known bars of this type that remain.
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
of gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
which they found in widespread use in pre-Columbian
Pre-Columbian
The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on the American continents, spanning the time of the original settlement in the Upper Paleolithic period to European colonization during...
Mesoamerica
Mesoamerica
Mesoamerica is a region and culture area in the Americas, extending approximately from central Mexico to Belize, Guatemala, El Salvador, Honduras, Nicaragua, and Costa Rica, within which a number of pre-Columbian societies flourished before the Spanish colonization of the Americas in the 15th and...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
Composition and properties
Tumbaga is an alloy composed mostly of gold and copper. It has a significantly lower melting pointMelting point
The melting point of a solid 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 on pressure and is usually specified at standard atmospheric pressure...
than gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
or copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
alone. It is harder than copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, but maintains malleability after being pounded.
Tumbaga can be treated with a simple acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
, like citric acid
Citric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
, 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
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:...
.
Use and function
Tumbaga was widely used by the pre-Columbian cultures of 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 gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
to copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
in artifacts varies widely; items have been found with as much as 97% gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
while others instead contain 97% copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
. 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 the lost wax technique and the alloy used was a mixture of copper (80%), silver (15%), and gold (5%). The indicated concentrations varied from object to object. Once the object was taken out of the cast, it was burned and as a consequence, copper from the surface of the object was oxidized to copper oxide and was then removed mechanically. The object was then placed in an oxidizing solution containing, it is believed, sodium chloride (salt), and ferric sulfate. This process removed through oxidation the silver from the surface of the object leaving only gold. When looking through a microscope, one may clearly see the empty spots from where the original elements copper and silver were removed.
The "Tumbaga" Wreck
In 1992, approximately 200 silver "tumbaga" bars were recovered in wreckage off Grand BahamaGrand Bahama
Grand Bahama is one of the northernmost of the islands of the Bahamas, and the closest major island to the United States, lying off the state of Florida. Grand Bahama is the fifth largest island in the Bahamas island chain of approximately 700 islands and 2,400 cays...
Island. They were composed of mainly silver, copper, and gold plundered by the Spaniards during the conquests of Cortés
Hernán Cortés
Hernán Cortés de Monroy y Pizarro, 1st Marquis of the Valley of Oaxaca was a Spanish Conquistador who led an expedition that caused the fall of the Aztec Empire and brought large portions of mainland Mexico under the rule of the King of Castile in the early 16th century...
and hastily melted into bars of tumbaga for transport across the Atlantic. Because all the metals that reached Europe were melted back into their constituent metals in Spain, the bars found in the shipwreck are the only known bars of this type that remain.