Gold is a soft yellow metal, while other metals (except copper) are silvery in appearance. It is the most malleable and ductile of all metals. Gold foil can be prepared by hammering the metal into very thin sheets. 1 gram of gold can be drawn into a wire more than 3 km in length. Pure gold is too soft to be used for jewelry and coins. For such purposes it is always alloyed with copper, silver or some other metal. The purity of gold is expressed in karats, a designation that indicates the number of parts, by weight, of gold in 24 parts of alloy. Thus 24- karat gold is the pure metal, while a 10- karat alloy is 10/24 gold by weight. Red or yellow gold alloys contain copper, and white gold contains palladium, nickel or zinc.