The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of fine metal therein, in proportion to the total weight which includes and any impurity. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. 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 in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.
Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of per mil
Millesimal fineness
Millesimal fineness is a system of denoting the purity of
platinum,
gold and
silver by
Per mille 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 "14 k", "18 k", etc., which is used in the United States, and the United Kingdom prior to the 1970s.
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 and the most common terms associated with them.
Platinum
-
999.95: what most dealers would buy as if 100% pure; the most common purity for platinum bullion coins and bars
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999— three nines fine
-
950: the most common purity for platinum jewelry
-
900— one nine fine
-
850
-
750
Gold
-
999.999— six nines fine: The purest gold ever produced. Refined by the Perth Mint in 1957.
-
999.99— five nines fine: The purest type of gold currently produced; the Royal Canadian Mint regularly produces commemorative coins in this fineness, including the world's largest, at 100 kg.
-
999.9— four nines fine: Most popular. 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.
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995: The minimum allowed in Good Delivery gold bars.
-
990— two nines fine
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986— Ducat fineness: Formerly used by Venetian and Holy Roman Empire mints; still in use in Austria and Hungary.
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965: Thai standard for gold purity. Often considered equivalent to 23 karat in this context.
-
958— 23 karat
-
916— 22 karat: Crown gold. Historically common for bullion coins, and currently used for British Sovereigns, Krugerrand, and the modern (1986—present) American Gold Eagles. Standard for jewelry in some countries such as India.
-
900— one nine fine: American Eagle denominations for 1837–1933; currently used in Latin Monetary Union mintage (e.g. French and Swiss "Napoleon coin" 20 francs).
-
899—American Eagles briefly for 1834–1836.
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834— 20 karat
-
750— 18 karat: Typical fineness for modern jewelry in most of Europe.
-
625— 15 karat
-
585— 14 karat: Most common fineness for jewelry in the United States.
-
500— 12 karat
-
417— 10 karat: Historically, the minimum standard for gold in the US. As of August 2018, any marked karat is permissible.
-
375— 9 karat: Minimum standard for gold in some of the Commonwealth realms: Australia, Canada, New Zealand, UK, etc. It is also the minimum in Austria, Ireland, Portugal and France.
-
333— 8 karat: Minimum standard for gold in Germany after 1884.
-
042– 1 karat: Legal minimum for gold in the US since the revision of the FTC Guides of August 2018.
Silver
-
999.99— five nines fine: The purest silver ever produced. This was achieved by the Royal Silver Company of Bolivia.
-
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. Used in U.S. silver commemorative coins and silver starting in 2019.
[ U.S. Mint abandons 90 percent silver composition]
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980: common standard used in Mexico ca. 1930–1945
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958: () Britannia silver
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950: French 1st Standard
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947.9: 91 zolotnik Russian silver
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935: Swiss standard for watchcases after 1887, to meet the British Merchandise Marks Act and to be of equal grade to 925 sterling. Sometimes claimed to have arisen as a Swiss misunderstanding of the standard required for British sterling. Usually marked with three Swiss bears.
-
935: used in the Art Deco period in Austria and Germany. Scandinavian silver jewellers used 935 silver after the 2nd World War
-
925: () Sterling silver. The UK has used this alloy from the early 12th century. Equivalent to plata de primera ley in Spain (first law silver)
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917: a standard used for the minting of Indian silver (rupees), during the British raj and for some coins during the first Brazilian Republic.
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916: 88 zolotnik Russian silver
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900: one nine fine, coin silver, or 90% silver: e.g. Flowing Hair and 1837–1964 U.S. silver coins. Also used in U.S. silver commemorative coins and silver 1982–2018.
-
892.4: US coinage fine "standard silver" as defined by the Coinage Act of 1792: e.g. Draped Bust and Capped Bust U.S. silver coins (1795–1836)
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875: 84 zolotnik is the most common fineness for Russian silver. Swiss standard, commonly used for export watchcases (also 800 and later 935).
-
868: 83 zolotnik. Imperial Russian coinage between 1797
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835: A standard predominantly used in Germany after 1884, and for some Dutch silver; 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; the French 2nd standard for silver; "plata de segunda ley" in Spain (second law silver); Egyptian silver; Canadian silver circulating coinage from 1920 to 1966/7
-
750: An uncommon silver standard found in older German, Swiss and Austro-Hungarian silver
-
720: Decoplata:
-
600: Used in some examples of postwar coins, such as the 1957-1966 100 yen coin
-
500: Standard used for making British coinage 1920–1946 as well as Canadian coins from 1967 to 1968, and some coins from Colombia and Brazil.
-
350: Standard used for US Jefferson nickel minted between 1942 and 1945.
Carat
The
carat (UK spelling, symbol
c or
Ct) or
karat (US spelling, symbol
k or
Kt)
is a fractional measure of purity for
gold alloys, in parts fine per 24 parts whole. The carat system is a standard adopted by US federal law.
Mass
- C = 24 × ( Mg / Mm)
where
- C is the carat rating of the material,
- Mg is the mass of pure gold in the alloy, and
- Mm is the total mass of the material.
24-carat gold is pure (while 100% purity is very difficult to attain, 24-carat as a designation is permitted in commerce for a minimum of 99.95% purity), 18-carat gold is 18 parts gold, 6 parts another metal (forming an alloy with 75% gold), 12-carat gold is 12 parts gold (12 parts another metal), and so forth.[ Comprehensive Jewelry Precious Metals Overview International Gem Society (IGS), Retrieved 01-16-2015]
In Britain, 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 fractional system is increasingly being complemented or superseded by the millesimal system, described above for bullion, though jewelry generally tends to still use the carat system.
Conversion between percentage of pure gold and karats:
-
58.33–62.50% = 14 c (acclaimed 58.33%)
-
75.00–79.16% = 18 c (acclaimed 75.00%)
-
91.66–95.83% = 22 c (acclaimed 91.66%)
-
95.83–99.95% = 23 c (acclaimed 95.83%)
-
99.95–100% = 24 c (acclaimed 99.95%)
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 other metals. The quantity of gold
by volume in a less-than-24-carat gold alloy differs according to the alloys 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/cm
3 for gold, 10.49 g/cm
3 for silver and 8.96 g/cm
3 for copper.
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 derived either from Italian carato or Medieval Latin carratus. These were borrowed into Medieval Europe from the
Arabic language qīrāṭ meaning "fruit of the carob tree", also "weight of 5 grains", (rtl=yes) and was a unit of mass
[ carat , Oxford Dictionaries] though it was probably not used to measure gold in classical times.
[ The Arabic term ultimately originates from the Greek language kerátion (κεράτιον) meaning carob seed (literally "small horn")][ κεράτιον , Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus][Walter W. Skeat (1888), An Etymological Dictionary of the English Language] (diminutive of κέρας – kéras, "horn"[ κέρας , Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus]).
In 309AD, Roman Emperor Constantine I began to mint a new gold coin, the solidus, that was of a libra (Roman pound) of gold
Verifying fineness
While there are many methods of detecting fake precious metals, there are realistically only two options available for verifying the marked fineness of metal as being reasonably accurate: assaying the metal (which requires destroying it), or using X-ray fluorescence (XRF). XRF will measure only the outermost portion of the piece of metal and so may get misled by thick plating.
That becomes a concern because it would be possible for an unscrupulous refiner to produce precious metals bars that are slightly less pure than marked on the bar. A refiner doing $1 billion of business each year that marked .980 pure bars as .999 fine would make about an extra $20 million in profit. In the United States, the actual purity of gold articles must be no more than .003 less than the marked purity (e.g. .996 fine for gold marked .999 fine), and the actual purity of silver articles must be no more than .004 less than the marked purity.
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 750 ‰ gold) may be said to have a fine weight of 0.75 troy ounces.
Most modern government-issued bullion coins specify their fine weight. For example, the American Gold Eagle is embossed One Oz. Fine Gold and weighs 1.091 troy oz.
Troy mass of silver content
Fineness of silver in Britain was traditionally expressed as the mass of silver expressed in Troy weight and pennyweights ( troy ounce) in one troy pound (12 troy ounces) of the resulting alloy. Britannia silver has a fineness of 11 ounces, 10 pennyweights, or about silver, whereas sterling silver has a fineness of 11 ounces, 2 pennyweights, or exactly silver.
See also
External links
