Fineness

The fineness of a precious metal refers to the ratio by weight of the primary metal to any added base metals or impurities. 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. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5%, by mass, of other metals, usually copper.

Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of parts per 1,000^[1] and karats used only for gold. Karats measure the parts per 24, so that 18 karat = 18/24 = 75% and 24 karat gold is considered 100% gold.^[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 karat system of denoting the purity of gold by fractions of 24, such as "18 karat" 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.

Here are the most common millesimal finenesses used for precious metals and the most common terms associated with them.

Platinum

999.5: what most dealers would buy as if 100% pure; the most common purity for platinum bullion coins and bars
999—three nines fine
950: the most common purity for platinum jewelry
925
900—one nine fine
850
750

Gold

999.999—six nines fine: the purest gold ever produced. Refined by the Perth Mint in 1957.^[3]^[4]
999.99—five nines fine: the purest type of gold currently produced; the Royal Canadian Mint regularly produces commemorative coins in this fineness
999.9—four nines fine: e.g., ordinary Canadian Gold Maple Leaf and American Buffalo coins
999—24 karat, also occasionally known as three nines fine: e.g., Chinese Gold Panda coins
995: the minimum allowed in Good Delivery gold bars
990—two nines fine
986—Ducat fineness: formerly used by Venetian and Holy Roman Empire mints; still in use in Austria and Hungary
958.3—23 karat
916—22 karat: historically the most widely used fineness for gold bullion coins; currently used for British Sovereigns, South African Krugerrands and American Gold Eagles
900—one nine fine: mostly used in Latin Monetary Union mintage (e.g. French and Swiss "Napoleon coin" 20 francs)
834—20 karat
750—18 karat
625—15 karat
585—14 karat
417—10 karat
376—9 karat
333—8 karat: minimum standard for gold in Germany after 1884^[5]

Silver

999.99—five nines fine: The purest silver ever produced. This was achieved by the Royal Silver Company of Bolivia.^[6]
999.9—four nines fine: ultra-fine silver used by the Royal Canadian Mint for their Silver Maple Leaf and other silver coins
999—fine silver or three nines fine: used in Good Delivery bullion bars and most current silver bullion coins
980: common standard used in Mexico ca. 1930–45
958—Britannia silver
950—French 1st Standard
925—Sterling silver
917: a standard used for the minting of Indian silver (rupees), during the British raj
916.66—11/12: the standard established by Maryland state law in 1814 for all silver sold in Baltimore. Last used in 1843.
900—one nine fine or 90% silver: e.g., all 1792–1964 U.S. silver coins
835: a standard predominantly used in Germany after 1884, and for the minting of coins in countries of the Latin Monetary Union
833: a common standard for continental silver especially among the Dutch, Swedish, and Germans
830: a common standard used in older Scandinavian silver
800: the minimum standard for silver in Germany after 1884; Egyptian silver; Canadian silver circulating coinage
750: an uncommon silver standard found in older German, Swiss and Austro-Hungarian silver
720: e.g., many Mexican and Dutch silver coins
500: Standard used for making British coinage after 1920

Karat

The karat (not carat as a unit of mass) (symbol: K or kt) (US) or carat (symbol: C)^[7]^[8] is a unit of purity for gold alloys.

Measure

Karat 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 karat 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 pure (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.^[9]

In England, the karat 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 karat system is increasingly being complemented or superseded by the millesimal fineness system, described above.

Conversion between percentage of pure gold and karats:

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%)
99.95–100% = 24K (acclaimed 99.99%)

Volume

However, this system of calculation gives only the mass of pure gold contained in an alloy. The term 18-karat 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-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 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 centimeters or in milliliters 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 centimeters or in milliliters,

M_{\text{a}}

is the total mass of the alloy in grams, and

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 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] Error: {{Lang}}: text has italic markup (help), from Italian [carato] Error: {{Lang}}: text has italic markup (help), both which came from Greek [kerátion] Error: {{Lang}}: text has italic markup (help) (κεράτιον) meaning carob seed (literally "small horn")^[10]^[11]^[12] (diminutive of κέρας - keras, "horn"^[13]), also from Arabic [qīrāṭ] Error: {{Lang}}: text has italic markup (help) meaning "fruit of the carob tree", also "weight of 4 grains", (قيراط) and was a unit of mass^[14] though it was probably not used to measure gold in classical times.^[10]

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^[15] equal to a mass of 24 siliqua, where each siliqua (or carat) was 1⁄1728 of a libra.^[16] This is believed to be the origin of the value of the karat.^[17]

Fine weight

A piece of alloy metal containing a precious metal may also 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.

Troy mass of silver content

Fineness of silver in Britain was traditionally expressed as the mass of silver expressed in troy ounces and pennyweights (1/20th of a Troy ounce), in one troy pound (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.

References

^ London Bullion Market Association. "Definitions".
^ Seyd, Ernest (1868). Bullion and foreign exchanges theoretically and practically considered. E. Wilson. p. 146. Retrieved 21 March 2012.
^ "The Perth Mint :: History". Gold Corporation. Retrieved 2011-05-08.
^ Thomas, Athol. 90 Golden Years, The story of the Perth Mint. Gold Corporation. p. 58.
^ "Fineness of Gold". Gold Rate for Today. Archived from the original on August 7, 2013. Retrieved 2013-08-15. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ http://www.royalsilver.com/about_us/about_us.html
^ Melaragno, Michele. The VNR Dictionary of Engineering Units and Measures. Van Nostrand Reinhold. p. 114.
^ The VNR OXFORD Dictionary for Scientific Writers and Editors. Oxford University Press. p. 56.
^ Comprehensive Jewelry Precious Metals Overview International Gem Society (IGS), Retrieved 01-16-2015
^ ^a ^b Harper, Douglas. "carat". Online Etymology Dictionary.
^ κεράτιον, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
^ Walter W. Skeat (1888), An Etymological Dictionary of the English Language
^ κέρας, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
^ carat, Oxford Dictionaries
^ Vagi, David L. (1999). Coinage and History of the Roman Empire. Vol. II: Coinage. Chicago: Fitzroy Dearborn. p. 100. ISBN 1-57958-316-4. Retrieved 18 November 2011.
^ Grierson, Philip (1968). Catalogue of the Byzantine Coins in the Dumbarton Oaks Collection and in the Whittemore Collection. Vol. 2: pt. 1. Washington, DC: Dumbarton Oaks. p. 8. ISBN 0-88402-024-X. Retrieved 18 November 2011.
^ 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.

External links

"Did carob seeds allow shady diamond deals?", New Scientist, Issue 2550 (9 May 2006), p. 20 (subscription required)

[1] London Bullion Market Association. "Definitions".

[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. Archived from the original on August 7, 2013. Retrieved 2013-08-15. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[6] ttp://www.royalsilver.com/about_us/about_us.html

[7] Melaragno, Michele. The VNR Dictionary of Engineering Units and Measures. Van Nostrand Reinhold. p. 114.

[8] The VNR OXFORD Dictionary for Scientific Writers and Editors. Oxford University Press. p. 56.

[9] Comprehensive Jewelry Precious Metals Overview International Gem Society (IGS), Retrieved 01-16-2015

[harper-10] Harper, Douglas. "carat". Online Etymology Dictionary.

[11] κεράτιον, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus

[12] Walter W. Skeat (1888), An Etymological Dictionary of the English Language

[13] κέρας, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus

[14] rat, Oxford Dictionaries

[15] Vagi, David L. (1999). Coinage and History of the Roman Empire. Vol. II: Coinage. Chicago: Fitzroy Dearborn. p. 100. ISBN 1-57958-316-4. Retrieved 18 November 2011.

[16] Grierson, Philip (1968). Catalogue of the Byzantine Coins in the Dumbarton Oaks Collection and in the Whittemore Collection. Vol. 2: pt. 1. Washington, DC: Dumbarton Oaks. p. 8. ISBN 0-88402-024-X. Retrieved 18 November 2011.

[17] 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.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]