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:''For other uses of the word "carat", see Carat.''
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 $frac\{1\}\{24\}$ purity by weight:
:
where
: $mathit\{X\}$ is the carat rating of the material,
: $M\_g$ is the mass of pure gold or platinum in the material, and
: $M\_m$ 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 $frac\{381\}\{384\}$ 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The karat system is increasingly being complemented or superseded by the millesimal fineness system in which the purity of precious metals is denoted by parts per thousand of pure metal in the alloy.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 karat (millesimal fineness 999)

★ 22 karat (millesimal fineness 916)

★ 20 karat (millesimal fineness 833)

★ 18 karat (millesimal fineness 750)

★ 15 karat (millesimal fineness 625)

★ 14 karat (millesimal fineness 585)

★ 10 karat (millesimal fineness 417)

★ 9 karat (millesimal fineness 375)

Contents

Derivation

Terminology

Volume

International Caratages of Gold Jewellery

Notes

References

See also

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 ^[1] 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'' ($frac\{1\}\{24\}$ 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 $frac\{1\}\{24\}$ of a golden solidus of Constantine; but was likely never used to measure the weight for gold.^[2]

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 allowed^[3][4]. 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
: $V\_mathit\{Au\}$ is the volume of gold in cm³ or in ml,
: $M\_a$ is the total mass of the alloy in grams, and
: $mathit\{kt\}$ 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

{|class="wikitable"
! width=40% | Region³
! width=40% | Typical Caratage (fineness)
|-
| Oriental East (China, Hong Kong, Taiwan) || 24 carat 'Chuk Kam' (99.0% min)
|-
| India & subcontinent || 22 carat (91.6%)
|-
| Arabic countries in Gulf region || 21 carat (87.5%), 18 carat (75.0%) in most Egypt
|-
| Europe - Southern / Mediterranean || 18 carat (75.0%)
|-
| Europe - Northern / USA etc || 8-18 carat (33.3 - 75.0%)
|-
| Russia / former USSR || 14 carat / old 583 and new 585 проба (58.5%)
|-

Notes

1. Turnbull ''et al.'' (2006)
2. Harper, (2001)
3. World Gold Council (2003)
4. Fallon, (2006)

References

★ Fallon, S. (2006) ''Hong Kong & Macau'', 12th ed., Melbourne ; London : Lonely Planet, ISBN 1-7405-9843-1

★ Harper, D. (2001) "Carat", in: ''Online Etymological Dictionary'', accessed 28 August 2007

★ New Scientist (2006) ''Did carob seeds allow shady diamond deals?'', New Scientist magazine, '2550' (09 May), p. 20

★ Turnbull, L.A., Santamaria, L., Martorell, T., Rallo, J. and Hector, A. (2006) "Seed size variability: from carob to carats", ''Biology Letters'', '2' (3: Sept. 22), p. 397–400, DOI 10.1098/rsbl.2006.0476

★ World Gold Council (2003) ''The Caratage (Karatage) System For Gold Jewellery'', Online article accessed 28 August 2007

See also

★ Gold as an investment

★ Gold bar

★ Gold coin

★ Platinum coin