The purity or fineness of silver alloys is now described using the Millesimal System in most countries. This system uses a number to represent the purity of the alloy. The number described purity in parts per thousand.
Previous to the Millesimal System, the fineness of silver was expressed in carats. While the fineness of silver alloys must be stamped or hallmarked into pieces, the Millesimal value is generally compulsory and the carat value now optional.
Pure silver is typically very soft and malleable, hence it is commonly alloyed to increase its hardness and durability for applications such as Jewelry. It is typically alloyed with copper in this instance, with sterling silver being one of the most popular alloys, containing 7.5% copper. Copper is used as it is a hardening agent and does not discolor the silver.
Weighing Precious Metals
The weight of a piece of gold jewelry is a factor that helps to determine its value. It is important because it is an indication of the amount of fine gold in an item of jewelry. Grams (g) and pennyweights (dwt) are the units of weight most commonly used in weighing gold. Gold and silver are almost always weighted in the troy system of weights where one pound troy equals twelve troy ounces and twenty pennyweights equals one troy ounce. The Avoirdupois weight system, where one pound equals 16 ounces, is used in the United States for most everything except precious metals.
grams (g); pennyweight (dwt); troy ounce (oz t); ounce avoirdupois (oz av)