- Tumbaga
Tumbaga was the name given by
Spaniards to a non-specificalloy ofgold andcopper which they found in widespread use inpre-Columbian Mesoamerica .Composition and properties
Tumbaga is an alloy composed mostly of gold and copper. It has a significantly lower
melting point thangold orcopper alone. It is harder thancopper , but maintainsmalleability after being pounded.Tumbaga can be treated with a simple
acid , likecitric 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 asdepletion gilding .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 tocopper 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.In
1992 , approximately 200 tumbaga bars were recovered in wreckage offGrand Bahama Island. They were composed of gold, copper, and silver plundered by theSpaniards during the conquests ofCortez andPizarro 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 tumbaga that remain.Fact|date=February 2007Some Mormon scholars suggest that the
Golden Plates from which the "Book of Mormon " was allegedly translated may have been made from tumbaga. [ [http://farms.byu.edu/display.php?table=jbms&id=393 "Of What Material Were the Plates?" article] from FARMS hosted by BYU]Orichalcum , the legendary metal of the island ofAtlantis , is commonly held to have been a gold-copper alloy, thus fitting the same description.Tumbaga objects were many times made by using the so called 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.
References
ee also
*
Tombac
*Corinthian bronze
*Shakudo External Links
* [http://www.sedwickcoins.com/shipwreck_histories/tumbaga.htm Shipwreck recovered right after the conquest of Cortés with tumbaga gold bars]
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