Gold is usually mixed with copper, zinc or silver to create an alloy suitable for use in jewelry. The ratio of gold to other elements varies, depending on the karat and the gold color.
According to Zales, 24-karat gold is 99.9 percent pure gold, and so, while the most valuable, is also the softest, making it prone to damage like scratching and bending. Nine-, 14- and 18-karat gold are all harder and more durable than 24-karat, but they have less gold. Rose gold has a high concentration of copper and some silver alloyed with the gold, red gold is a mixture of gold and copper, and white gold alloys gold with platinum or palladium.