The American Gold Eagle, one of the most widely held investment coins in the world, isn’t pure gold. It’s 22 karat, which means it’s 91.7% gold with silver and copper alloy. That’s by design. Pure gold is soft, and a coin that can’t hold up to handling isn’t practical.
Here, we walk through what a gold alloy is, how the karat system measures purity, which metals are commonly used, and what alloy content means when you’re buying gold for investment.
What is a gold alloy?
A gold alloy is a mixture of gold and one or more other metals. The added metals are usually copper, silver, palladium, nickel, or zinc. They change the gold’s hardness, color, and reduce its purity.
Pure gold, also called 24 karat, is 99.9% gold with no other metals. It’s dense, bright yellow, and soft. That softness makes it impractical for most applications. When you add copper, the metal becomes harder and more durable. Add palladium, and it turns white. Add more copper, and it shifts toward rose.
How the karat system works
Karat measures how much of a gold alloy is gold. The scale runs from 1 to 24, with 24 karat being pure gold.
Here’s an overview of karat levels:
| Karat | Gold content | Purity stamp | Common use |
| 24k | 99.9% | 999 | Bullion gold bars, some coins |
| 22k | 91.7% | 916 | Investment coins |
| 18k | 75.0% | 750 | Fine jewelry |
| 14k | 58.3% | 585 | Everyday jewelry |
| 10k | 41.7% | 417 | Lower-cost jewelry |
The stamp on a gold product tells you the purity. A bar stamped 999 is 99.9% pure gold and a ring stamped 585 is 58.5% gold.
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What metals are used in gold alloys?
Different metals produce different results.
- Copper: This alloy adds hardness and durability. Higher copper content creates what people call rose gold. It’s the most common additive in gold alloys.
- Silver: Adds hardness while keeping the color close to yellow gold. It’s used alongside copper in many investment coins.
- Palladium: One of the white gold alloys without the allergy concerns that nickel can cause. It’s more expensive, which is why white gold varies in price.
- Nickel: This common alloy is a lower cost way to produce white gold.
- Zinc: This alloy adds hardness and helps with casting. It’s used in smaller amounts and rarely the primary additive.
Gold alloys in investment coins
Before the 1930s, gold alloy coins were commonly used in circulating currency, as pure gold was too soft for everyday transactions. Today, here’s how the most widely held investment coins compare:
| Coin | Karat | Gold content | Other metals |
| American Gold Eagle | 22k | 91.7% | Silver, copper |
| South African Krugerrand | 22k | 91.7% | Copper |
| Canadian Gold Maple Leaf | 24k | 99.99% | No intentional alloy metals |
| Austrian Gold Philharmonic | 24k | 99.99% | No intentional alloy metals |
| American Gold Buffalo | 24k | 99.99% | Non |
The American Gold Eagle uses a 22-karat alloy for durability. The added silver and copper make it harder and more resistant to scratching. The total gold content is still one troy ounce in a standard coin. The alloy metals are added on top, which is why a one-ounce Gold Eagle weighs slightly more than a troy ounce.
The Maple Leaf and Gold Buffalo are 24 karat with no added metals. They’re slightly more delicate because pure gold scratches more easily, but many investors prefer the higher purity level.
For Gold IRAs, the IRS requires gold to be at least 99.5% pure. That rules out 22-karat coins except the American Gold Eagle. The IRS approves it for Gold IRAs as a special exception because it’s a U.S. Mint coin.
Does alloy content matter for investors?
For physical gold investors, the most important number is the actual gold content, not the karat rating. A one-ounce Gold Eagle contains one troy ounce of gold regardless of the added metals.
Where karat matters more is in jewelry. A 14k gold ring is 58.3% gold. You’re paying for the full weight of the piece, but only a portion of it is gold. That’s why most investors stick to bullion coins and bars priced on their actual gold content.
Final thoughts on gold alloys
A 22-karat Gold Eagle and a 24-karat Maple Leaf both contain real gold, and both hold value as physical precious metals. The alloy content tells you how the coin was made. The gold content tells you what you own.
To learn more about investing in gold and other precious metals, connect with the Swiss America team today!
Gold alloy: FAQs
Is gold alloy real gold?
Yes. A gold alloy is real gold mixed with other metals. The added metals don’t replace the gold. Instead, they share space with it, which is why the karat rating tells you exactly how much gold is in any piece.
- How dealers treat it: Precious metals dealers and refiners value gold alloys based on their actual gold content. A 22 karat coin is bought and sold on the one troy ounce of gold it contains, not on its total weight including the alloy metals.
- What gold-plated means instead: Gold-plated jewelry is not a gold alloy. Plating puts a thin gold coating on a base metal core. A gold alloy contains gold throughout the entire piece, not just on the surface.
- How to confirm it’s genuine: Look for a purity stamp. Legitimate gold alloys are stamped with their fineness: 999 for 24 karat, 916 for 22 karat, 750 for 18 karat. No stamp, or a stamp that doesn’t match the stated karat, is a red flag.
What is the best gold purity for investing?
For most physical gold investors, 24 karat and 22 karat are the best choices. The decision usually comes down to if you’re buying coins or bars.
- Bars: Gold bars from recognized mints are 24 karat at .999 or .9999 fine.
- Coins: Gold Eagle and Krugerrand are 22 karat each and have been among the most traded investment coins in the world for decades.
What does .9999 fine gold mean?
It means the gold is 99.99% pure with four nines of fineness, compared to the three nines (99.9%) you see on most standard bullion.
- Diffrences: The Canadian Gold Maple Leaf is one of the few investment coins struck to .9999 fineness. Most bullion bars from LBMA-approved refiners are also .9999. Standard 24 karat products are typically .999, still considered pure gold but with a slightly higher trace-metal allowance.
- Impact: The difference in gold content between .999 and .9999 is less than one-tenth of a percent per ounce. For most investors holding a few ounces, this is negligible.
- Stamp: A product at .9999 fineness is stamped ‘9999’ rather than ‘999.’ Both stamps indicate 24 karat gold. The extra digit signals the higher refinement standard, not a different karat classification.
How do you know what karat your gold is?
The most reliable place to start is the purity stamp. Every legitimate gold product carries a hallmark that tells you its gold content.
- Reading the stamp: Fineness stamps read as parts per thousand: 999 means 99.9% gold (24 karat), 916 means 91.6% gold (22 karat), 750 means 75% gold (18 karat), 585 means 58.5% gold (14 karat).
- When there’s no stamp: A reputable jeweler or precious metals dealer can test gold using acid testing, electronic testing, or X-ray fluorescence (XRF). XRF reads the exact alloy composition without damaging the piece and is the most precise option.
- Older gold: Antique gold items may carry older hallmarking systems or stamps from foreign mints that don’t follow standard fineness notation. A professional assay is the safest way to confirm purity on any piece without a recognizable modern stamp.
Does higher gold purity mean higher value?
Per troy ounce of gold, the purity level doesn’t change the value. A one-ounce Gold Eagle and a one-ounce Maple Leaf both track the same gold spot price. What changes is how much of the total weight is gold.
- Where purity affects pricing: A 14-karat ring might weigh 10 grams, but only 5.85 of those grams are gold. You’d pay for all 10 grams at retail, but when you sell, you’re paid based on the gold content. The higher the karat, the closer those two numbers get.
- 24 karat coins with higher premiums: Coins like the Maple Leaf sometimes command a slightly higher dealer premium than 22 karat coins of the same gold weight. Part of that reflects demand, especially in Asian markets where buyers pay more for .999 or .9999 fine gold. The underlying gold value is identical.
- The resale implication: Investment-grade bullion at 22 karat or higher trades on its actual gold content, so purity differences between these tiers have minimal effect on what you receive when you sell. The bigger gap is between investment-grade bullion and retail jewelry, where gold content can be well below 22 karat.
The information in this post is for informational purposes only and should not be considered tax or legal advice. Please consult with your own tax professionals before making any decisions or taking action based on this information.
