What does 10k, 14k or 18k gold mean and how is it tested?

Karat tells you how much of the metal is pure gold, measured in 24ths. Pure gold is 24k. 18k is 75% gold, 14k is 58.3% gold, and 10k is 41.7% gold, with the rest being metals like copper, silver and zinc that add hardness and color. European pieces are often stamped with numbers instead: 750 for 18k, 585 for 14k and 417 for 10k.

A stamp is a good start but not proof. Fake and misleading stamps exist, so buyers test. The traditional method is the acid test: the piece is rubbed on a black touchstone and acids of different strengths are applied to the streak to see which ones dissolve it. Many shops also use electronic testers, and some use X-ray fluorescence (XRF) machines that read the metal content without damaging the piece.

If a piece has no stamp, it may still be gold, especially older or handmade jewelry. Ask a gold buyer to test it while you watch, and ask what karat they found.