Gold has been used in jewelry making for thousands of years and is the most popular jewelry metal today. Because of its high malleability (among metals, only silver is more malleable), gold can be manipulated into intricate designs. It does not fade, rust, or corrode, and it is very resistant to tarnishing. As you know, gold is also expensive. Only one other metal, platinum, is pricier than gold.

Gold Content in Jewelry - Karats

Because gold is very soft, it's usually alloyed with other, harder metals. Alloyed gold is less prone to scratching and deformation over time, making jewelry more durable. The amount of pure gold in a piece of jewelry is measured by the "karatage" system. Every piece of gold jewelry should be labeled with a small metal stamp indicating its karatage. These stamps are called "karat marks." They typically depict a number followed by the letter "k."

Karat marks indicate the amount of pure gold in 24ths. Pure gold is described as 24 karat (or "24k"). If you divided a 24-karat piece of jewelry into 24 equal units, all 24 would be pure gold. A 10 karat piece of jewelry divided into 24 equal units would contain 10 units of pure gold and 14 units of other, nonprecious metals.

Here are the most common karat marks used today in the United States and Europe:

In the United States, all gold jewelry is required by law to contain a karat mark, and the minimum legal karatage for jewelry sold in the U.S. is 10 karat. Gold content may be as low as 9 karat in the United Kingdom, and as low as 8 karat in Germany. Twenty-four karat gold jewelry is rare in the U.S. and Europe, but is a traditional wedding gift in China and Hong Kong.

Gold Colors

In its pure (24 karat) form, gold is deep yellow-orange with a slightly dull finish. When gold is alloyed with other metals, its color changes subtly or dramatically, depending on the alloy. It also becomes shinier. Yellow gold typically contains copper and silver. White gold contains copper, nickel, and zinc. (This is important to remember if you're allergic to nickel.) Gold can even be colored "rose," green, or "red" when alloyed with various amounts of copper, zinc, and/or aluminum.

Editor's pick:

These 14 karat yellow gold hoops are a bestsellers on Amazon.com for their simplicity, style (hoops are back!), and affordability.

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Stay tuned for the next three articles in this series:

Gold Jewelry - Prices

Gold Jewelry - Care and Storage