Walk into any jewelry store, including ours, and chances are you won't find one even piece of jewelry made from pure gold! It's true. Pure gold is slightly reddish yellow in color and is 24 karat by definition. 18K gold is 75% pure gold. 14K gold is 58.5% pure gold. And 10K gold is 41.7% pure gold.
Pure gold is soft and pliable -- and thus usually considered undesirable for use in rings and other items of jewelry. Other metals called alloys are used to strengthen gold. And to change its color!
Yellow gold alloys
Yellow gold is a combination of metals including gold, copper, and silver. Yellow gold is the only color of gold that can be described as 24 karat; the other commonly seen golds, white gold and rose gold, require other metals to create their colors. (White and rose golds do not occur naturally.)
While you may occasionally see 24K and 22K yellow gold jewelry, these karatages aren't commonly used in the United States. You will most often see 18K, 14K, and 10K yellow gold.
Wondering what else, then, is in that gold band you are wearing?
- 18K yellow gold: 75% fine gold, 15% copper, 10% fine silver
- 14K yellow gold: 58.5% fine gold, 29% copper, 12.5% fine silver
- 10K yellow gold: 37.5% fine gold, 52% silver, 4.9% copper, 4.2% zinc and 1.4% nickel
White gold alloys
White gold is an alloy of gold and one or more white metals. The most commonly used white metals are silver, zinc, nickel, manganese, and palladium. There are numerous recipes for white gold and because each metal has its own qualities, there are always advantages and disadvantages to a particular combination. So while there is no standard white gold alloy, remember there will always be the same amount of pure gold in the mix. Like yellow gold, the most frequently seen pieces of white gold jewelry will come in 14K or 18K. Here are some common formulas:
- 18K white gold: 75% fine gold, 10% copper, 8% nickel, 4.5% zinc
- 14K white gold: 58.5% fine gold, 12% copper, 8% nickel, 6% zinc, 4.5% fine silver
Very likely, you've heard of -- or experienced yourself -- nickel allergies. People with nickel allergies have to be careful when choosing white gold. As you can see from above, nickel is a pretty standard ingredient in white gold. But some white gold is created with palladium instead. Palladium is awesome because it's hypoallergenic. It's also a strong, durable metal with a bright white hue -- and less likely to show a yellow cast like nickel. But because it's part of the platinum family, it's also more expensive.
The other really important thing to keep in mind about white gold is that, despite its name, it isn't actually white! White gold is usually a grayish-yellow color but can also show tinges of brown or rose. This is normal (if disappointing). Jewelers often counter this effect by rhodium plating white gold jewelry. This makes the piece a bright, sparkling white! Rhodium plating is part of routine jewelry maintenance and a white gold ring will have to be re-plated from time to time.
Rose gold alloys
Rose gold is a mixture of gold and copper. And the more copper in the mix, the darker "red" the rose gold will be. You will generally have 14K and 18K rose gold to choose from. Remember 14K gold has less pure gold than 18K gold, so when we're talking about rose gold there is more room for copper in 14K gold than 18K gold. 14K rose gold tends be warm and rosy while 18K rose gold is a softer color, like rose-tinged champagne.
Here are some examples of the metal content in rose gold:
- 18K rose gold: 75% fine gold, 22% copper, 1% zinc and 1% fine silver
- 14K rose gold: 58.5% fine gold, 36% copper, 2.5% fine silver, and 1% zinc
Green gold alloys
Green gold has been known since Antiquity by the name electrum. Electrum is a naturally-occurring alloy of silver and gold -- and is more of a greenish-yellow rather than green.
Usually you will see, if you see it at all, green gold used to create a color contrast with other gold alloys in multicolored jewelry pieces, such as pendants and so on. The greenish tinge is just perceptible. Most green gold alloys are based on a traditional gold-silver-copper system, and typically contain high concentrations of silver. These green golds are fairly soft. Recently, zinc has been used in the mix and apparently results in an acceptable color with improved hardness:
18K green gold: 75.0% pure gold, 6-7% fine silver, 9-11.7% copper, and 6.5-9% zinc
Purple gold alloy
Believe it or not! Purple gold is not only for extraterrestrials, we have it here on Earth. Purple gold is an intermetallic compound. These are a special group of materials with properties very different from the individual metals that constitute them. They are usually brittle, which make their use in jewelry not exactly desirable. Intermetallic metals, like purple gold, can, however, be faceted and used as gemstones or inlays. Purple gold is formed from 79% gold and 21% aluminum.
A new Purple Gold™ has been invented by Dr. Low Peng Chum, a Singaporean metallurgist. It is being promoted as the world's first malleable purple gold and described as 80% pure gold and 20% of other metal components.
Blue gold alloy
Blue gold is another intermetallic compound. It is composed of 46% gold (about 12 karat) and 54% indium -- and has a slight bluish cast.
Some artists also veneer jewelry with blue gold alloys. For example, a deep sapphire blue colored gold can be created by alloying pure gold with ruthenium, rhodium, and other elements.
Direct contact of blue and purple gold elements with skin is something to avoid as exposure to sweat may result in metal leaching and discoloration of the metal surface.
Black gold alloy
There are many methods for creating black gold such as electroplating using rhodium or ruthenium, oxidation, and patination (think patina!). Pure gold can be mixed with cobalt and when it's heated to a certain temperature will form a black oxide layer. Other recipes add chromium to the recipe. Black gold is always used as a surface treatment or a veneer -- as we described with the blue gold.