The primary types of gold contain different purities, which are measured in karats. Gold overlay refers to items that are made from a non-gold metal that is permanently coated with gold. To be considered gold overlay, the gold weight must equal at least 10 percent of the total weight. Gold is available in yellow, white and rose colors, which are created by mixing it with other metals.
Pure gold is 24-karat gold, which is very pliable and, therefore, unsuitable for jewelry. Eighteen-karat gold is 75 percent gold and 25 percent alloy metals, while 14 karat gold is at least 58.3 percent gold. Ten-karat gold is the lowest standard measure and is at least 41.7 percent gold. The higher karat numbers indicate a higher gold weight. Gold-plated items are made through the same process as gold overlay, but these items only need to contain 5 percent of at least 10-karat gold. Yellow gold is the most traditional color for jewelry and is made of gold blended with copper, zinc and silver. White gold is gold alloyed with copper zinc and nickel. It looks similar to sterling silver, but it does not tarnish like silver. Rose gold is gold mixed with copper and sometimes silver. It is a warm, pink color.