| Carat (purity) |
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The carat (abbreviation '''ct''' or '''K''') is a measure of the Purity of Gold and Platinum Alloys . In the United States and Canada , the spelling ''karat'' is now solely used for the measure of purity, while ''carat'' solely refers to the measure of mass weight (''see Carat (mass) ''). As a measure of purity, one karat is purity by weight: : where : is the carat rating of the material, : is the mass of pure gold or platinum in the material, and : is the total mass of the material. Therefore 24 carat gold is pure (100% Au w/w), 18-carat gold is 75% gold, 12-carat gold is 50% gold, and so forth. Historically, in England the carat was divisible into four grains, and the grain was divisible into four quarts. For example, a gold alloy of fineness (that is, 99.2% purity) could have been described as being ''23-carat, 3-grain, 1-quart gold''. The karat system is increasingly being complemented or superseded by the Millesimal Fineness system in which the purity of Precious Metal s is denoted by parts per thousand of pure metal in the alloy. The most common carats used for gold in Bullion , Jewellery making and by goldsmiths are:
DERIVATION The word ''carat'' is derived from the Greek ''kerátiōn'' (κεράτιων), “fruit of the Carob ”, via Arabic ''qīrāṭ'' (قيراط) and Italian . Carob seeds were used as weights on precision scales because of their reputation for having a uniform weight. However, a 2006 study Turnbull ''et al.'' (2006) by Lindsay Turnbull and others found this to not be the case – carob seeds have as much variation in their weights as other seeds.New Scientist (2006) — review of Turnbull ''et al.'' (2006). In the distant past, different countries each had their own carat, roughly equivalent to a carob seed. In the mid-16th century, the carat was adopted as a measure of gold purity, roughly equivalent to the Roman ''siliqua'' ( of a golden Solidus of Constantine I ). As a measure of diamond weight, from 1575, the Greek measure was the equivalent of the Roman siliqua, which was of a golden solidus of Constantine; but was likely never used to measure the weight for gold.Harper, (2001) TERMINOLOGY ''22/22K'' - a quality mark indicating the purity of Gold . The first 22 signifies the "Skin purity" of gold jewellery and the second 22 signifies that after melting purity of the gold jewellery will be 22K (22 Karat ) or 91.67% of pure gold. This symbol or stamp is very popular on the gold jewellery business in Asian countries like India , Pakistan , Bangladesh , Nepal , Yemen , and Gulf Countries. This practice was pioneered and introduced in the early mid-1980s by Nemichand Bamalwa & Sons of Kolkata, India , sparking a revolution in India as it forced jewellers to indicate correctly the after-melting purity, and heightened consumer awareness made it a most sought-after stamp or quality mark. ''Chuk Kam'' - In Chinese the term means pure gold. It is defined as 99.0% gold minimum with a 1.0% negative tolerance allowedWorld Gold Council (2003)Fallon, (2006). The quality of gold is guaranteed with a "Certificate of Gold" upon purchases in Hong Kong and Macau . VOLUME However, this system of calculation gives only the weight of pure gold contained in an alloy. The term ''18-karat gold'' means that the alloy's weight consists of 75% of gold and 25% of alloy(s). The quantity of gold by volume in a less than 24-karat gold alloy differs according to the alloy(s) used. For example, knowing that standard 18-karat yellow gold consists of 75% gold, 12.5% silver and the remaining 12.5% of copper (all by weight), the volume of pure gold in this alloy will be 60% since gold is much more dense than the alloys used: 19.32 g/cm³ for gold, 10.49 g/cm³ for silver and 8.96 g/cm³ for copper. This formula gives the amount of gold in cm³ or in ml in an alloy: : where : is the volume of gold in cm³ or in ml, : is the total mass of the alloy in grams, and : is the karat purity of the alloy. To have the percentage of the volume of gold in an alloy, divide the volume of gold in cm³ or in ml by the total volume of the alloy in cm³ or in ml. For 10-karat gold, the gold volume in the alloy represents about 26% of the total volume for standard yellow gold. One should be aware of this, since talking about purity according to weight could lead to some misunderstandings; for many people, purity means volume. INTERNATIONAL CARATAGES OF GOLD JEWELLERY NOTES REFERENCES
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