[Jewelry making - Article 00299] - Re: [Orchid] Tumbago alloy

[Rick Martin]

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    Tumbaga was used in pre-Columbian times (roughly from 600 A.D. on)
    from Central America to Peru and Chile as a generic term for any
    combination of gold and copper.  It could range from 95% copper to
    95% gold, although tumbaga or guanin gold was usually made by adding
    10 to 30% copper to gold. Tumbaga usually contains 5 to 10% silver as
    well, which occurred naturally in the gold and wasn't intentionally
    added.  That?s the definition given in "Sweat of the Sun, Tears of
    the Moon" and another source I have. 

    There were several reasons tumbaga was popular.  A primary one is
    that 70% gold/30%copper will melt at around 800 C., much lower than
    gold or copper separately.  That's important because melts were done
    in large clay pots using a team of men huffing on blowpipes. 
    (There?s an amazing Moche clay urn I've seen that shows this
    procedure in detail). Molten metal then flowed from a hole in the
    bottom of the vessel into open molds made from stone or clay.  These
    molds have been found archaeologically from Mexico to Chile. 

    The lost wax casting techniques of these peoples were very
    sophisticated as well. They routinely cast hollow objects and bimetal
    part silver-part gold objects using complex one-time molds made of
    ground charcoal, sand and clay. Depletion gilding was routinely used
    to decorate the surfaces of objects made from low-gold alloys. The
    amount of gold used in tumbaga depended on the metal?s availability. 
    Objects from gold-rich areas like Calima and Tolima in Colombia, for
    instance, were large and contained purer gold while most pieces from
    the Muisca and Tairona regions were smaller, less pure and depended
    on gilding for appearance. 

    Tumbaga had another interesting use as well.  Some cultures like the
    Moche placed small tumbaga ingots in the mouths of their high-ranking
    dead prior to burial.  I?ve encountered this same ritual using
    various metals while studying the burial practices of several other
    ancient cultures around the world but am not clear on its
    significance. 

    In the bibliography of "Sweat of the Sun, Tears of the Moon," the
    following sources are listed: 

    Coggins, Clemency Chase. "Artifacts from the Cenote of Sacrifice
    Chichen Itza, Yucatan." Ed. Clemency Chase Coggins Vol. 10/No. 3
    Cambridge, The President and Fellows at Harvard College, 1992. 

    Jones, Julie.  "The Art of Precolombian Gold: The Jan Mitchell
    Collection." Ed. Julie Jones.  Boston Little, Brown and Company,
    1985. 

    Nottebohm, Karl-Heinz.  "A Second Tlaloc Gold Plaque from Guatemala.
     Notes on Middle American Archaeology and Ethnography."  Vol. 2
    Numbers 31=60.  New York AMS Press, 1969. 

    Weaver, Muriel Porter.  "The Aztecs, Maya, and their Predecessors;
    Archaeology of Mesoamerica."  Third Ed.  San Diego, Academic Press,
    1993. 

    I have a wonderfully detailed article, "Gold of El Dorado:
    Technology of Ancient Colombian Gold" by Clemencia Plazas and Ana
    Maria Falchettie de Saenz that appeared in ?Natural History?
    (November 1979, Vol. 88, No. 9, pp. 36-46). 

    If it?s still in print, "Royal Tombs of Sipan" by Walter Alva and
    Christopher B. Donnan is a beautifully produced and illustrated
    showcase of Moche gold and silver work.  It was published in
    conjunction with a traveling exhibition from UCLA?s Fowler Museum. 
    The ISBN of my softbound (expensive enough!) is 0-930741-30-7. 

Rick Martin
MARTIN DESIGNS


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