Pure gold, or 24-karat, is generally considered too soft for use in jewelry, so gold is alloyed with other metals to increase its strength
Eighteen-karat gold is 18/24ths, or three-quarters, pure gold. Jewelry of this fineness is marked “18k” or “750”, the European designation meaning 75 percent gold. In the United States, 14-karat gold is used most commonly for jewelry. Fourteen-karat gold is 14/22ths, or slightly more than one-half, pure gold. Jewelry of this fineness is marked “14k” or “585”, the European designation meaning of 58.5 percent gold.
Because gold is alloyed with other metals to increase its strength, it can also be made in a variety of colors. For example, yellow gold is created by alloying the metal with copper and silver. Pricing is based on four factors: caratage, weight, design, and craftsmanship. The caratage and weight tell you how much gold is in a piece, but construction and design are also crucial factors in determining price.