Tumbaga
Alloys · Uncommon · Ancient
The Spanish name for the alloys of gold and copper, often with silver, that the peoples of pre-Columbian Central and South America cast, in proportions ranging from nearly all gold to nearly all copper. Treated with an oxidising solution, likely of salt and ferric sulfate, the surface loses its copper and a skin of gold is left over the alloy: depletion gilding.
Identity
- Source
- Pre-Columbian Mesoamerican and Andean civilizations
- Composition
- Gold, Copper, Silver
- Over time
- The proportions vary widely, from 97% gold to 97% copper; a usual cast alloy for depletion gilding was copper, silver and gold in about 80:15:5.
- Also known as
- Guanín
- Ores, before industry and since
- Gold (Gold), Sylvanite (Gold), Azurite (Copper), Chalcocite (Copper), Chalcopyrite (Copper), Copper (Copper), Malachite (Copper), Tetrahedrite (Copper), Acanthite (Silver), Chlorargyrite (Silver), Freibergite (Silver), Galena (Silver), Proustite (Silver), Pyrargyrite (Silver), Silver (Silver), Tetrahedrite (Silver)
- Ores of the industrial age
- Calaverite (Gold), Bornite (Copper), Chrysocolla (Copper), Covellite (Copper), Cuprite (Copper), Enargite (Copper)
Physical Properties
- Appearance
- Warm reddish-gold surface over a copper-rich core; acid-treated pieces show pure gold exteriors
- Luster
- Metallic
- Density
- 11 g/cm³
- Melting point
- 950 °C
- Boiling point
- 1800 °C
- Lighter
- Uru
- Denser
- Adamantium
- Magnetism
- Non-magnetic
- Electrical conductivity
- High
Mechanical Properties
- Mohs hardness
- 3.5
- Tensile strength
- 300 MPa
- Softer
- Shakudo
- Harder
- Hepatizon
- Workability
- Easy
- Brittleness
- Moderate
- Malleability
- Very High
- Ductility
- High
Chemical Properties
- Corrosion resistance
- Moderate
- Reactivity
- Low
Lore & Narrative
The Taíno called such an alloy guanín and prized it for its reddish lustre and its smell; Spanish assayers in 1498 found guanín of about 56% gold, 18% silver and 25% copper. The conquistadors melted the tumbaga they took back into its metals in Spain.
- Notable uses
- Pectorals, votive figures, jewellery
- Forge uses
- Masks, Figurines, Jewelry
- Worldbuilding traits
- Alchemical, Transformation, Sacred, Precolumbian
Sources
- Tumbaga, Wikipedia
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