The karat mark will tell you that the piece is real and how much pure gold it contains. Pure gold (24K) is rarely used because it is soft and damages easily. Gold is typically mixed with other metals, like silver, nickel, copper and zinc, which makes it more durable. Proportions of these alloys are adjusted to give the gold its green, rose or white tint.

Karats are different than "carats," the weight measure used for diamonds and other gems.
18K gold is 75%, 14K is 58.5%, and 10K is 41.6%. The more karats, the richer the color.

In the U.S. jewelry must be at least 10K to be legally considered and sold as real gold. (In Canada and Mexico, the minimum legal standard of karatage is 9K and 8K respectively.)

Imported gold jewelry is often stamped with a number which is the percentage of gold times 100. The European markings for 14 karat gold jewelry is 585 or 58.5% ,and for 18K is 750 or 75%.