Most gold jewelry isn’t made of pure gold.
The amount of gold in a necklace or ring is measured on the karat scale. Pure gold is 24 karats. Bars of gold kept in Fort Knox and elsewhere around the world are considered to be 99.95 percent pure, 24-karat gold.
As metals are added to gold during jewelry making, the gold becomes less fine and the number of karats drops. For example, 12 karat gold contains 50 percent gold and 50 percent alloys by weight.
The word karat comes from the carob seed. In ancient Asian bazaars, the seeds were used to balance scales that measured the weight of gold.