White gold is an alloy of gold and at least one white metal, such as silver or palladium. Like yellow gold, white gold is measured in karats. Its properties vary depending on the metals and proportions used. As a result, white gold alloys can be used for different purposes; while a nickel alloy is hard, strong and therefore good for rings and pins, white gold-palladium alloys are soft, pliable and good for white gold gemstone settings. The highest quality white gold is usually at least 17 karat, and made up of gold and palladium, and sometimes even trace levels of platinum for weight and durability, although this often requires specialized goldsmiths.