Fineness

The fineness of a precious metal refers to the ratio by weight of the primary metal to any added base metals or impurities traditionally expressed as parts per 1,000.[1]

A piece of alloy metal containing a precious metal may have the weight of its precious component referred to as its fine weight. For example, 1 troy ounce of 18 karat gold (which is 75% gold) may be said to have a fine weight of 0.75 troy ounces.

Many precious metals are used in the form of alloys. Other metals are added to increase hardness, to make the metal more practical for use in such items as coins and jewelry, or to decrease the cost of the alloy. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry.

A traditional measure for the fineness of silver in Britain is the mass of the amount of silver in 12 troy ounces of the resulting alloy. Britannia silver has a fineness of 11 troy ounces, 10 pennyweights, or about 95.83% silver, whereas sterling silver has a fineness of 11 troy ounces, 2 pennyweights, or about 92.5% silver. In other locations fineness is measured in units of mass per thousand. In the United States, silver coins often had a fineness of 900, meaning 90% silver and 10% copper.

The fineness (or purity) of gold is commonly measured in carats or karats. The upper end of the scale is 24 carat for 100%. Thus 18 carat = 18/24 = 75%.[2]

Millesimal fineness

Millesimal fineness is a system of denoting the purity of platinum, gold and silver alloys by parts per thousand of pure metal by mass in the alloy. For example, an alloy containing 75% gold is denoted as "750". Many European countries use decimal hallmark stamps (i.e. '585', '750', etc.) rather than '14K', '18K', etc., which is used in the United Kingdom and United States.

It is an extension of the older carat (karat in North American spelling) system of denoting the purity of gold by fractions of 24, such as "18 carat" for an alloy with 75% (18 parts per 24) pure gold by mass.

The millesimal fineness is usually rounded to a three figure number, particularly where used as a hallmark, and the fineness may vary slightly from the traditional versions of purity.

The most common millesimal finenesses used for precious metals (and the most common terms associated with them):

Platinum

Gold

Silver

Carat

The carat or karat (symbol: K or kt) is a unit of purity for gold alloys.

Measure

Carat purity is measured as 24 times the pure mass divided by the total mass:

K = 24\,\frac{M_\text{g}}{M_\text{m}}

where

K is the carat rating of the material,
M_\text{g} is the mass of pure gold in the alloy, and
M_\text{m} is the total mass of the material.

Therefore, 24-karat gold is fine (also includes down to 99.95% gold by mass), 18-karat gold is 18 parts gold, 6 parts another metal (forming an alloy with 75% gold), 12-karat gold is 12 parts gold (12 parts another metal), and so forth.[6]

In England, the carat was divisible into four grains, and the grain was divisible into four quarts. For example, a gold alloy of \tfrac{381}{384} fineness (that is, 99.2% purity) could have been described as being 23-karat, 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; e.g. 18-karat gold, 75% Au, would be called 750.

Karat conversion:

58.33% - 62.50% = 14k (acclaimed 58.33%)
75.00% - 79.16% = 18k (acclaimed 75.00%)
91.66% - 95.83% = 22k (acclaimed 91.66%)
95.83% - 99.95% = 23k (acclaimed 95.83%)
99.95 and above = 24k (acclaimed 99.99%)

Volume

However, this system of calculation gives only the mass of pure gold contained in an alloy. The term 18-carat gold means that the alloy's mass consists of 75% of gold and 25% of alloy(s). The quantity of gold by volume in a less-than-24-carat gold alloy differs according to the alloy(s) used. For example, knowing that standard 18-carat yellow gold consists of 75% gold, 12.5% silver and the remaining 12.5% of copper (all by mass), the volume of pure gold in this alloy will be 60% since gold is much denser than the other metals 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 cubic centimetres or in millilitres in an alloy:

V_\text{Au} = \frac{M_\text{a} \times \tfrac{kt}{24}}{19.32}

where

V_\text{Au} is the volume of gold in cubic centimetres or in millilitres,
M_\text{a} is the total mass of the alloy in grams, and
kt is the carat purity of the alloy.

To have the percentage of the volume of gold in an alloy, divide the volume of gold in cubic centimetres or in millilitres by the total volume of the alloy in cubic centimetres or in millilitres.

For 10-carat gold, the gold volume in the alloy represents about 26% of the total volume for standard yellow gold. Talking about purity according to mass could lead to some misunderstandings; for many people, purity means volume.

Etymology

Karat is a variant of carat. First attested in English in the mid-15th century, the word carat came from Middle French carat, in turn from Italian carato, which came from Arabic qīrāṭ (قيراط), which came from Greek kerátion (κεράτιον) meaning carob seed (literally "small horn")[7][8][9] (diminutive of κέρας - keras, "horn"[10]) and was a unit of mass[11] though it was probably not used to measure gold in classical times.[7]

In 309 CE, Roman Emperor Constantine I began to mint a new gold coin solidus that was 1⁄72 of a libra (Roman pound) of gold[12] equal to a mass of 24 siliqua, where each siliqua (or carat) was 1⁄1728 of a libra.[13] This is believed to be the origin of the value of the karat.[14]

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 gold jewelry, and the second 22 signifies that after melting purity of the gold jewellery will be 22-karat, or 91.67% of pure gold. This system is used to show consistency in the quality of the gold.

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. Heightened consumer awareness made it a most sought-after stamp or quality mark.

This symbol or stamp can be found in such Asian countries as India, Sri Lanka, Pakistan, Bangladesh, Nepal, Yemen, and Persian Gulf countries.

Region[15] Typical caratage (fineness)
International caratages of gold jewellery
Arabic countries, Far East (China, Hong Kong, Taiwan), Malaysia, Indonesia 24-karat "Chuk Kam" (99.0% min)
Arabic countries, Bangladesh, India, Pakistan, Nepal, and Sri Lanka 22-karat (91.6%)
Arabic countries in the Persian Gulf region 21-carat (87.5%)
Europe - Southern / Portugal 19.2-karat (80.0%)
Europe - Southern / Mediterranean 18-karat (75.0%)
Europe - Northern Germany, Scandinavia 8 to 18-karat (33.3-75.0%)
Iran, Brazil, Egypt 18-karat (75.0%)
Russia and the rest of the former Soviet Union 9 (37.5%) and 14 (58.3%) karat/old and new 14.04-karat (58.5%) 585 проба
United Kingdom 9-carat to 22-carat (37.5-91.6%)
United States, Canada 10-karat to 18-karat (41.7-75%)
Turkey 14-karat to 22-karat (58.3-91.6%)

Chinese gold standards

Pure gold (足金, lit. "full gold") is known Zú jīn in Mandarin, and chuk kam in Cantonese. It is defined as 99.0% gold minimum with a 1.0% negative tolerance allowed.[15][16] The quality of gold is guaranteed with a "certificate of gold" upon purchases in Hong Kong and Macau. The related term "千足" and "万足" meaning "thousand exact" and "ten thousand exact" is also used for purity of 99.9% and 99.99% respectively. This is because the impurity is at most 1 in 1,000 in the case of 99.9% or 1 in 10,000 for 99.99%.

United States

The US Federal Trade Commission (FTC) has standardized the karat markings used within its boundaries since the 1940s. Under these regulations, items 10-karat 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 law in the United States. There are specific mandated consequences including fines, etc., based upon the severity of the infraction(s).

In addition, there is a set of tolerances to the required karat markings in the United States (designated with a "K" ) depending upon the use of various soldering requirements when setting stones, mounting crowns, or creating prongs, for example.[17]

See also

References

  1. ↑ London Bullion Market Association. "Glossary of Terms".
  2. ↑ Seyd, Ernest (1868). Bullion and foreign exchanges theoretically and practically considered. E. Wilson. p. 146. Retrieved 21 March 2012.
  3. ↑ "The Perth Mint :: History". Gold Corporation. Retrieved 2011-05-08.
  4. ↑ Thomas, Athol. 90 Golden Years, The story of the Perth Mint. Gold Corporation. p. 58.
  5. ↑ "Fineness of Gold". Gold Rate for Today. Retrieved 2013-08-15.
  6. ↑ Comprehensive Jewelry Precious Metals Overview International Gem Society (IGS), Retrieved 01-16-2015
  7. ↑ 7.0 7.1 Harper, Douglas. "carat". Online Etymology Dictionary.
  8. ↑ κεράτιον, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  9. ↑ Walter W. Skeat (1888), An Etymological Dictionary of the English Language
  10. ↑ κέρας, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  11. ↑ carat, Oxford Dictionaries
  12. ↑ Vagi, David L. (1999). Coinage and History of the Roman Empire. II: Coinage. Chicago: Fitzroy Dearborn. p. 100. ISBN 1-57958-316-4. Retrieved 18 November 2011.
  13. ↑ Grierson, Philip (1968). Catalogue of the Byzantine Coins in the Dumbarton Oaks Collection and in the Whittemore Collection. 2: pt. 1. Washington, DC: Dumbarton Oaks. p. 8. ISBN 0-88402-024-X. Retrieved 18 November 2011.
  14. ↑ Turnbull, L. A.; Santamaria, L.; Martorell, T.; Rallo, J.; Hector, A. (2006). "Seed size variability: From carob to carats". Biology Letters 2 (3): 397–400. doi:10.1098/rsbl.2006.0476. PMC 1686184. PMID 17148413.
  15. ↑ 15.0 15.1 "Gold Karatage - Gold Colours - Hallmarks". World Gold Council. Retrieved October 8, 2014.
  16. ↑ Fallon, Steve (2006). Hong Kong & Macau (12th ed.). Melbourne: Lonely Planet. ISBN 1-74059-843-1.
  17. ↑ Title 16: Commercial Practices: Part 23—Guides for the jewelry, precious metals, and pewter industries

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