What tumbaga is
Tumbaga is a gold and copper alloy. Metalsmiths in pre-Columbian Central and South America used it from about 500 BCE to the 1500s. Gold content in surviving pieces runs from 5 percent to 95 percent. The balance is copper, with small amounts of silver. A frequent mix is 70 to 80 percent gold and 20 to 30 percent copper. Workers heated the finished object in acid to dissolve copper at the surface. That left a gold-rich skin. The method is called mise en couleur, or depletion gilding.
Tumbaga is not a Cartier term. Cartier has not sold a tumbaga watch.
How the word is used in the replica trade
Sellers use "tumbaga" for gold-color replica Cartier cases made from a gold and copper alloy instead of solid 18K gold or plating over steel. The mix in these cases sits near 75 percent gold and 25 percent copper, which copies the color of 18K yellow gold. Some cases are cast from a lower gold mix, then given an acid dip to raise the gold content at the surface.
Models sold under this label include the Santos, Tank, Ballon Bleu, and Panthere in yellow gold finish. Case sizes copy the genuine range, from 27 mm to 43 mm.
Density numbers
- Fine gold: 19.3 g/cm3
- 18K yellow gold: about 15.5 g/cm3
- 75/25 gold-copper alloy: about 14.6 g/cm3
- Brass: about 8.5 g/cm3
- Gold-plated steel: about 7.9 g/cm3
A tumbaga case weighs less than a solid 18K case of the same size. The gap runs 5 to 8 percent by volume. On a 40 mm watch that is several grams.
Tests you can run
- Magnet. Gold, copper, and brass do not pull a magnet. A steel core does.
- Weight. Put the watch on a gram scale and compare with a published weight for the same reference.
- Acid. Nitric acid attacks copper and leaves 18K gold. Test an inside surface, not the dial side.
- X-ray fluorescence. Reports gold, copper, and silver percentages. A jeweler charges $20 to $50.
- Hallmarks. Genuine Cartier gold cases carry 750 or 18K plus a maker mark and a case number. Shallow laser marks with no depth point to a replica.
- Wear points. Copper-rich alloys darken at the crown, lugs, and caseback edges within months of daily wear.
What tumbaga does not do
Copper reacts with sweat and skin acids. Green or black marks on the wrist appear after a few weeks. Polishing strips the gold-rich skin and exposes a darker alloy underneath. Cartier service centers decline these watches, so no parts and no repair. Resale value is near zero.
Legal status in the US
Selling a watch as Cartier when Cartier did not make it is trademark infringement. The FTC Jewelry Guides bar gold claims on base metal. Customs can seize shipments. Personal ownership is a separate matter from sale, but the item still carries no warranty and no service support.
Bottom line
Tumbaga is a real historic alloy, not a Cartier material. A gold-color replica case stamped with a Cartier name is a copy part, whatever the seller calls the metal. Density, magnet, acid, and XRF results give a clear answer in under an hour.