Yellow gold is gold mixed with smaller amounts of silver, copper and sometimes zinc. Pure gold is too soft for most jewelry, so jewelers add these metals for strength and to adjust the color. The karat number on a piece tells you how much of it is gold, from 24K (pure) down to 9K or 10K, depending on the country.
Gold as a metal
Gold is one of the noble metals. It does not rust, tarnish or corrode in air or water, and it dissolves only in unusual chemicals such as aqua regia. It is the most malleable metal known: a single gram can be beaten into a sheet covering about a square meter. It is also dense, at about 19.3 g/cm³, which is why gold jewelry feels heavy in the hand.
Pure gold has a warm, deep yellow color. Every other shade of gold in jewelry comes from mixing it with other metals. Add more copper and the alloy turns pink or red, as in rose gold. Add nickel or palladium and it turns pale gray, as in white gold. Yellow gold stays closest to the natural color.
The karat system
Gold purity is measured in karats, with 24 karats meaning pure gold. Each karat is one twenty-fourth of the total weight. The word comes from the carob seed, once used as a small weight, and the same root gives the carat used to weigh gemstones. The two units are different: a gemstone carat is 0.2 grams, while a karat is a share of purity.
Many countries also mark gold in parts per thousand, called millesimal fineness. The table shows the common standards.
| Karat | Gold content | Fineness mark | Where it is common |
|---|---|---|---|
| 24K | 99.9 percent (pure for trade purposes) | 999 | China, bullion, some Asian jewelry |
| 22K | 91.6 percent | 916 | India, the Middle East, British sovereigns |
| 18K | 75 percent | 750 | Europe, fine jewelry worldwide |
| 14K | 58.5 percent | 585 | United States, Germany |
| 10K | 41.7 percent | 417 | United States (lowest legal "gold") |
| 9K | 37.5 percent | 375 | United Kingdom, Ireland, Australia |
In the United States, an item must be at least 10K to be sold as gold. The United Kingdom allows 9K as its lowest hallmarking standard. Some countries also accept 8K (333). Buyers in India, China and parts of the Middle East have long preferred 22K and 24K gold, where jewelry has also been a way to hold savings in metal.
What goes into a yellow gold alloy
The metals mixed with gold are called the alloy. In yellow gold they are mainly silver and copper, often with a little zinc. Silver pushes the color toward greenish yellow. Copper pushes it toward orange and red. Zinc lightens the color, helps the metal flow during casting and reduces oxide on the surface.
At 18K, a balanced mix of silver and copper gives the familiar rich yellow. With a lot of silver and no copper, the result is the pale "green gold" used in some antique jewelry. At 14K and 10K, more of the piece is alloy, so the color is paler and less saturated than 18K or 22K. Standard yellow alloys differ between manufacturers, so two 14K pieces can show slightly different shades.
Hardness versus purity
Pure 24K gold is soft. It bends easily, scratches quickly and cannot hold a small stone securely in a thin prong. Copper and silver atoms of a different size from gold's distort the crystal lattice and make the alloy harder. That is why a 14K ring usually resists dents and scratches better than an 18K ring of the same design, and both outlast a 22K band in daily wear.
Lower karat gold has trade-offs too. It contains more base metal, so it can tarnish slightly over many years, especially in contact with chlorine or sulfur compounds. Some low-karat alloys can also crack under stress if the metal is exposed to harsh chemicals while it is under tension, such as a tightly bent prong in a swimming pool. A goldsmith working with gold also hardens it by hammering and softens it again by heating, a process covered on the annealing gold page.
For engagement rings and other pieces worn daily, 14K and 18K are the usual choices. 14K gives more resistance to wear. 18K gives a richer color and contains more gold. 22K and 24K suit pieces that see little abrasion, such as pendants and earrings, and bands made in cultures that prefer high purity.
Weight and price factors
Since gold is denser than its usual alloy metals, an 18K piece weighs more than a 14K piece of the same size, and a 22K piece more again. Jewelry made in higher karats costs more for two reasons: it contains a higher share of gold, and it has more gold by weight. The final price of a gold piece also includes design, labor, stones and the seller's margin, so the metal value alone rarely explains the tag.
Solid gold, gold-filled and gold-plated
Yellow gold color can sit on top of other metals. Under the US Federal Trade Commission's jewelry guides:
- Gold-filled (GF) or rolled gold plate (RGP) describes a layer of at least 10K gold mechanically bonded to a base metal. Gold-filled must have gold equal to at least one-twentieth of the item's weight, often marked "1/20 14K GF."
- Gold electroplate (GEP) and gold-plated (GP) describe a very thin layer applied by electroplating.
- Vermeil describes sterling silver coated with gold of at least 10K and a minimum thickness of about 2.5 microns.
Plating and fill wear through with time, exposing the metal underneath. A mark such as "14K GP" or "18KGE" describes a plated item and should not be read as solid gold. The hallmarks guide covers these stamps along with the karat marks.
Hallmarks and stamps
Solid gold jewelry usually carries a karat mark (14K, 18K) or a fineness number (585, 750). In the United Kingdom, Ireland and other hallmarking countries, an independent assay office tests the metal before marking it. In the United States, the maker or seller applies the mark, which must be accompanied by the maker's trademark. Older American pieces sometimes say "14K plumb," meaning the gold meets the full stated karat.
Care and pairing with gemstones
Yellow gold needs little care beyond cleaning. Warm water, mild soap and a soft brush remove skin oils and lotion residue. Keep gold away from chlorinated pools and hot tubs, which can attack the alloy metals in lower karats. The jewelry cleaning guide covers which gemstones tolerate ultrasonic cleaners.
Yellow gold flatters warm-colored gems such as citrine, ruby and emerald. It can make a near-colorless diamond look slightly warmer, which is why many yellow gold rings use white metal prongs to hold the diamond. The overview of jewelry metals compares gold with platinum, palladium and silver.
Frequently asked questions
Is 24K gold good for rings?
Pure gold is soft and scratches and bends with daily wear. A 24K band will show marks quickly, so most rings are made in 14K or 18K for durability.
Why does my 10K gold look paler than 18K?
10K gold is less than half gold, and the rest is alloy metal. That dilutes the yellow color, so lower karats look paler and less saturated.
What does 585 mean on gold jewelry?
It is the fineness mark for 14K gold, meaning 585 parts per thousand of the metal is gold. Some makers mark 583 for the same standard.
Does yellow gold tarnish?
High-karat gold does not tarnish. Lower karats such as 9K and 10K contain more silver and copper and can darken slightly over years of exposure to sulfur or chlorine.