Have you ever heard of tumbaga? This intriguing precious metal alloy played a unique role in the Age of Exploration, and continues making a splash today in modern science. The term “tumbaga” is Spanish, referring to a gold-copper alloy widely used in pre-Columbian Mesoamerica and South America. It was coined by Spanish conquistadors who discovered heaps of the metal on their quest to find riches throughout the Americas in the 16th century.
Ancient Alloys
“Tumbaga” likely originates from the Malay word tembaga, meaning copper or brass. The alloy is comprised of gold and copper, sometimes with silver mixed in too. The proportions of each metal vary significantly with different objects and uses. Tumbaga is valued because it is harder than pure copper yet malleable like gold, making it ideal for crafting.
While some gold alloys occur often in nature, such as the gold-silver alloy known as electrum, native gold-copper is less common. This is why tumbaga primarily refers to a human-made alloy.
Ancient cultures in Central and South America used tumbaga to craft decorative pieces, religious objects, musical instruments, jewelry and more. Its relatively low melting point made it easier to work with than pure gold or copper.
A Surprising Discovery
The conquistadors who encountered tumbaga were searching for pure gold, not gold-copper alloys. One particularly misleading discovery took place in Panama around 1519 AD. A fleet of conquistadors had promised the Spanish court a mass of gold in exchange for investing in their dangerous transatlantic voyage. The explorers had expected the region to be rich in gold mines – but to their disappointment, the mines eluded them. They sadly resorted to looting gold items from the indigenous people, some even robbing grave goods from cemeteries.
Once the Spaniards began to melt down their hoard, they realized that barely any of it was made of pure gold. It was actually tumbaga! Many of the items contained large amounts of copper, some with as little as 20% gold.
One would think that an alloy with so much copper would have a reddish tint, giving the looters a clue about its composition – but on the outside, the objects looked very much like pure gold. It was later discovered that this effect was achieved through a process called depletion gilding.
Ancient Techniques: Depletion Gilding
Depletion gilding is a fascinating process that historians believe was developed among the cultures of ancient Peru as early as 400 BC. It was likely used throughout Mesoamerica at least a millennium before the conquistadors arrived. The technique involved treating a tumbaga alloy with a simple acid (like citric acid), essentially dissolving the copper from the surface, leaving behind a paper-thin outer layer of pure gold.
Tumbaga Today
Gold-copper alloys have been used by artisans for centuries and are still popular today, especially in jewelry-making. Rose gold, for example, is technically a modern-day form of tumbaga – it’s a gold-copper alloy that’s valued for its unique color and durability.
Beyond that, Au–Cu alloys have gained prominence in nanoscience, mostly for catalysis – they catalyze a wide range of chemical reactions from carbon monoxide oxidationto selective oxidation of alcohols. Gold nanoparticles also show exciting promise in medicine, including cancer treatments and diagnostic testing.
The “Tumbaga” Shipwreck
Throughout history, many shipwrecks have revealed treasures of precious metals, gemstones, and artifacts. In 1992 about 200 silver bars were recovered from a shipwreck near Grand Bahama Island. These bars weren’t pure silver, but rather a mixture of silver, copper, and gold: tumbaga.
The conquistadors had melted these metals into tumbaga bars during Hernán Cortés’ conquests, making them easier to transport across the Atlantic. Once back in Spain, the bars were typically melted again to separate and purify the metals. This process – refining – is exactly what we specialize in here at Garfield Refining.
Precious Metal Alloys
Tumbaga’s rich history continues to influence modern science and craftsmanship. Even alloys high in copper could potentially hold significant value if they contain enough gold – especially with today’s record-breaking prices, which recently surpassed $3,600 per troy ounce!
If you have unwanted rose gold jewelry, 14k jewelry, or other gold items that you’re looking to monetize, a trusted refinery like Garfield can help you maximize their value. We specialize in refining precious metals like gold, silver, platinum and palladium, providing industry-leading payouts and award-winning customer service. If you have precious metal items that you think may be worth refining, reach out today to discuss your options!
If you enjoyed this post, check out other articles like ‘Unexpected Uses of Precious Metals’ or ‘How is Gold Used in Space Exploration?’
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