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Carat (purity)
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The carat (abbreviation ct or kt) is a measure of the purity of gold alloys. In the United States and Canada, the spelling karat is used, while the spelling carat is used to refer to the measure of mass for gemstones (see Carat (mass)).
measure of purity, one carat is purity by mass:
-
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 fine (99.9% 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.
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The carat (abbreviation ct or kt) is a measure of the purity of gold alloys. In the United States and Canada, the spelling karat is used, while the spelling carat is used to refer to the measure of mass for gemstones (see Carat (mass)).
Measure
As a measure of purity, one carat is purity by mass:
-
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 fine (99.9% 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The carat system is increasingly being complemented or superseded by the millesimal fineness system in which the purity of precious metals is denoted by parts per thousand of pure metal in the alloy.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:
- 24 carat (millesimal fineness 999)
- 22 carat (millesimal fineness 916)
- 20 carat (millesimal fineness 833)
- 18 carat (millesimal fineness 750)
- 15 carat (millesimal fineness 625)
- 14 carat (millesimal fineness 585)
- 10 carat (millesimal fineness 417)
- 9 carat (millesimal fineness 375)
- 8 carat (millesimal fineness 333)
- 1 carat (millesimal fineness 042)
Derivation
The word carat is derived from the Greek kerátion (?e??t???), “fruit of the carob”, via Arabic qira? and Italian. Carob seeds were used as weights on precision scales because of their reputation for having a uniform weight. This was not the only reason. It is said that in order to keep regional buyers and sellers of gold honest, a potential customer could retrieve their OWN carob seeds on their way to the market, to check the tolerances of the seeds used by the merchant. If this precaution was not taken, the potential customer would be at the mercy of "2 sets of carob seeds". One set of "heavier" carob seeds would be used when buying from a customer (making the seller's gold appear to be less). Another, lighter set of carob seeds would be used when the merchant wanted to SELL to a customer.
However, a 2006 study by Lindsay Turnbull and others found this to not be the case – carob seeds have as much variation in their weights as other seeds. In the distant past, different countries each had their own carat, roughly equivalent to a carob seed. In the mid-16th century, the Karat 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.
Terminology
22/22K - a quality mark indicating the purity of gold most popularly used in India. This purity was adapted and practiced by the big jewellers and was later passed to jewel smiths. The first 22 signifies the "Skin purity", the purity of the top layer of the of gold jewelry, and the second 22 signifies that after melting purity of the gold jewellery will be 22-carat, or 91.67% of pure gold. This system is used to show consistency in the quality of the gold.
This symbol or stamp is very popular on the gold jewellery business in Asian countries like India, Sri Lanka, Pakistan, Bangladesh, Nepal, Yemen, and Persian 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
Chuk Kam in Cantonese (Chinese) means pure gold, literally "exact gold". It is defined as 99.0% gold minimum with a 1.0% negative tolerance allowed. The quality of gold is guaranteed with a "Certificate of Gold" upon purchases in Hong Kong and Macau.
In the United States of America
The USA Federal Trade Commission (FTC) has legislated and standardized the karat markings used within its boundaries for almost 7 decades now. Under these regulations, items 10K or greater are to be stamped with either "K" or "Kt." Decimal markings are also an option under the CFTC regulations.
Under karating is against the USA law. There are specific mandated consequences including fines, et al., based upon the severity of the infraction(s).
Additionally, there are a set of tolerances to the required karat markings in the USA (always designated with a "K" and never a "C") depending upon the use of various soldering requirements when setting stones, mounting crowns, or creating prongs for 3 examples.
Title 16: Commercial Practices
PART 23—GUIDES FOR THE JEWELRY, PRECIOUS METALS, AND PEWTER INDUSTRIES
§ 23.4 Misrepresentation as to gold content.
(a) It is unfair or deceptive to misrepresent the presence of gold or gold alloy in an industry product, or the quantity or karat fineness of gold or gold alloy contained in the product, or the karat fineness, thickness, weight ratio, or manner of application of any gold or gold alloy plating, covering, or coating on any surface of an industry product or part thereof.
(b) The following are examples of markings or descriptions that may be misleading:2
2 See §23.4(c) for examples of acceptable markings and descriptions.
(1) Use of the word “Gold” or any abbreviation, without qualification, to describe all or part of an industry product, which is not composed throughout of fine (24 karat) gold.
(2) Use of the word “Gold” or any abbreviation to describe all or part of an industry product composed throughout of an alloy of gold, unless a correct designation of the karat fineness of the alloy immediately precedes the word “Gold” or its abbreviation, and such fineness designation is of at least equal conspicuousness.
(3) Use of the word “Gold” or any abbreviation to describe all or part of an industry product that is not composed throughout of gold or a gold alloy, but is surface-plated or coated with gold alloy, unless the word “Gold” or its abbreviation is adequately qualified to indicate that the product or part is only surface-plated.
(4) Use of the term “Gold Plate,” “Gold Plated,” or any abbreviation to describe all or part of an industry product unless such product or part contains a surface-plating of gold alloy, applied by any process, which is of such thickness and extent of surface coverage that reasonable durability is assured.
(5) Use of the terms “Gold Filled,” “Rolled Gold Plate,” “Rolled Gold Plated,” “Gold Overlay,” or any abbreviation to describe all or part of an industry product unless such product or part contains a surface-plating of gold alloy applied by a mechanical process and of such thickness and extent of surface coverage that reasonable durability is assured, and unless the term is immediately preceded by a correct designation of the karat fineness of the alloy that is of at least equal conspicuousness as the term used.
(6) Use of the terms “Gold Plate,” “Gold Plated,” “Gold Filled,” “Rolled Gold Plate,” “Rolled Gold Plated,” “Gold Overlay,” or any abbreviation to describe a product in which the layer of gold plating has been covered with a base metal (such as nickel), which is covered with a thin wash of gold, unless there is a disclosure that the primary gold coating is covered with a base metal, which is gold washed.
(7) Use of the term “Gold Electroplate,” “Gold Electroplated,” or any abbreviation to describe all or part of an industry product unless such product or part is electroplated with gold or a gold alloy and such electroplating is of such karat fineness, thickness, and extent of surface coverage that reasonable durability is assured.
(8) Use of any name, terminology, or other term to misrepresent that an industry product is equal or superior to, or different than, a known and established type of industry product with reference to its gold content or method of manufacture.
(9) Use of the word “Gold” or any abbreviation, or of a quality mark implying gold content (e.g., 9 karat), to describe all or part of an industry product that is composed throughout of an alloy of gold of less than 10 karat fineness.
Note to paragraph(b)§23.4: The provisions regarding the use of the word “Gold,” or any abbreviation, as described above, are applicable to “Duragold,” “Diragold,” “Noblegold,” “Goldine,” “Layered Gold,” or any words or terms of similar meaning.
(c) The following are examples of markings and descriptions that are consistent with the principles described above:
(1) An industry product or part thereof, composed throughout of an alloy of gold of not less than 10 karat fineness, may be marked and described as “Gold” when such word “Gold,” wherever appearing, is immediately preceded by a correct designation of the karat fineness of the alloy, and such karat designation is of equal conspicuousness as the word “Gold” (for example, “14 Karat Gold,” “14 K. Gold,” or “14 Kt. Gold”). Such product may also be marked and described by a designation of the karat fineness of the gold alloy unaccompanied by the word “Gold” (for example, “14 Karat,” “14 Kt.,” or “14 K.”).
Note to paragraph(c)(1): Use of the term “Gold” or any abbreviation to describe all or part of a product that is composed throughout of gold alloy, but contains a hollow center or interior, may mislead consumers, unless the fact that the product contains a hollow center is disclosed in immediate proximity to the term “Gold” or its abbreviation (for example, “14 Karat Gold-Hollow Center,” or “14 K. Gold Tubing,” when of a gold alloy tubing of such karat fineness). Such products should not be marked or described as “solid” or as being solidly of gold or of a gold alloy. For example, when the composition of such a product is 14 karat gold alloy, it should not be described or marked as either “14 Kt. Solid Gold” or as “Solid 14 Kt. Gold.”
(2) An industry product or part thereof, on which there has been affixed on all significant surfaces, by any process, a coating, electroplating, or deposition by any means, of gold or gold alloy of not less than 10 karat fineness that is of substantial thickness,3 and the minimum thickness throughout of which is equivalent to one-half micrometre (or approximately 20 millionths of an inch) of fine gold,4 may be marked or described as “Gold Plate” or “Gold Plated,” or abbreviated, as, for example, G.P. The exact thickness of the plate may be marked on the item, if it is immediately followed by a designation of the karat fineness of the plating which is of equal conspicuousness as the term used (as, for example, “2 micrometres 12 K. gold plate” or “2µ 12 K. G.P.” for an item plated with 2 micrometres of 12 karat gold.)
3 The term substantial thickness means that all areas of the plating are of such thickness as to assure a durable coverage of the base metal to which it has been affixed. Since industry products include items having surfaces and parts of surfaces that are subject to different degrees of wear, the thickness of plating for all items or for different areas of the surface of individual items does not necessarily have to be uniform.
4 A product containing 1 micrometre (otherwise known as 1µ) of 12 karat gold is equivalent to one-half micrometre of 24 karat gold.
Note to paragraph(c)(2): If an industry product has a thicker coating or electroplating of gold or gold alloy on some areas than others, the minimum thickness of the plate should be marked.
(3) An industry product or part thereof on which there has been affixed on all significant surfaces by soldering, brazing, welding, or other mechanical means, a plating of gold alloy of not less than 10 karat fineness and of substantial thickness5 may be marked or described as “Gold Filled,” “Gold Overlay,” “Rolled Gold Plate,” or an adequate abbreviation, when such plating constitutes at least1/20th of the weight of the metal in the entire article and when the term is immediately preceded by a designation of the karat fineness of the plating which is of equal conspicuousness as the term used (for example, “14 Karat Gold Filled,” “14 Kt. Gold Filled,” “14 Kt. G.F.,” “14 Kt. Gold Overlay,” or “14K. R.G.P.”). When conforming to all such requirements except the specified minimum of1/20th of the weight of the metal in the entire article, the terms “Gold Overlay” and “Rolled Gold Plate” may be used when the karat fineness designation is immediately preceded by a fraction accurately disclosing the portion of the weight of the metal in the entire article accounted for by the plating, and when such fraction is of equal conspicuousness as the term used (for example, “1/40th 12 Kt. Rolled Gold Plate” or “1/4012 Kt. R.G.P.”).
5 See footnote 3.
(4) An industry product or part thereof, on which there has been affixed on all significant surfaces by an electrolytic process, an electroplating of gold, or of a gold alloy of not less than 10 karat fineness, which has a minimum thickness throughout equivalent to .175 micrometres (approximately7 /1,000,000ths of an inch) of fine gold, may be marked or described as “Gold Electroplate” or “Gold Electroplated,” or abbreviated, as, for example, “G.E.P.” When the electroplating meets the minimum fineness but not the minimum thickness specified above, the marking or description may be “Gold Flashed” or “Gold Washed.” When the electroplating is of the minimum fineness specified above and of a minimum thickness throughout equivalent to two and one half (21/2) micrometres (or approximately100 /1,000,000ths of an inch) of fine gold, the marking or description may be “Heavy Gold Electroplate” or “Heavy Gold Electroplated.” When electroplatings qualify for the term “Gold Electroplate” (or “Gold Electroplated”), or the term “Heavy Gold Electroplate” (or “Heavy Gold Electroplated”), and have been applied by use of a particular kind of electrolytic process, the marking may be accompanied by identification of the process used, as for example, “Gold Electroplated (X Process)” or “Heavy Gold Electroplated (Y Process).”
(d) The provisions of this section relating to markings and descriptions of industry products and parts thereof are subject to the applicable tolerances of the National Stamping Act or any amendment thereof.6
6 Under the National Stamping Act, articles or parts made of gold or of gold alloy that contain no solder have a permissible tolerance of three parts per thousand. If the part tested contains solder, the permissible tolerance is seven parts per thousand. For full text, see 15 U.S.C. 295, et seq .
Note 4 to paragraph(d): Exemptions recognized in the assay of karat gold industry products and in the assay of gold filled, gold overlay, and rolled gold plate industry products, and not to be considered in any assay for quality, are listed in the appendix.
International caratages of gold jewellery
See also
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