Those earrings, necklaces, bracelets and rings you have accumulated over the years may be stamped with phrases such as 22K, 24K or .999 Gold. You may have wondered on occasion what those phrases mean. If you do see one of those terms inscribed on your jewelry, be happy. You are in possession of some very fine gold items.
Standard of Measurement
Gold marked 22K or 24K is measured using the carat (karat) measure of gold purity, while .999 gold is measured using the millesimal fineness system. The carat measure is actually represented by a formula that equals the ratio of the mass of pure gold in the object to the mass of the whole object. Then that ratio is multiplied by 24. The millesimal fineness system is different in that it reports purity as a decimal in ppt (parts per thousand).
Gold designated 24K is the purest gold commonly available. It indicates that an object contains 99 percent pure gold. All other carat measurements are essentially determined in comparison to the purity of 24K gold. For instance, 22K gold indicates 92.5 percent pure gold (because 22/24 has a decimal equivalence of .925) and .999 gold is considered by many experts to be equal to 24K gold, if not purer.
Each of these three gold measurements can be found in jewelry and gold bullion, but there are still other differences among the three in terms of how they are used. Because 24K, 22K and .999 gold contain such high quantities of pure gold, they are too soft to be used in jewelry. They are often combined with other metals to create an alloy for jewelry making. Generally, the purer the gold, the lower the amount of other metals found in the alloy. So only 24K and .999 gold jewelry can legally be called "pure gold." Also, 24K and .999 gold are seen more often in gold bullion (bars, coins and ingots) than 22K gold. which does not meet the purity standards for the finest bullion.
Certain gold measurements are standards in some countries and not in others; 22K gold is the standard and most commonly seen purity measurement in India and other central Asian countries. In China and some other southeast Asian countries, 24K gold is the standard.