Fineness


The fineness of a precious metal object represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. 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 silver coins 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 parts per 1,000 and karats or carats used only for gold. Karats measure the parts per 24, so that 18 karat = = 75% gold and 24 karat gold is considered 100% gold.

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 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% 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 for them are:

Platinum

  • 999.95: 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
  • 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 in production; 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.
  • 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.
  • 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, South African Krugerrands, and the modern American Gold Eagles. Standard for jewelry in some countries such as India.
  • 900—one nine fine: American Eagle denominations for 1837–1933; used in Latin Monetary Union mintage.
  • 899—American Eagles briefly for 1834–1836.
  • 834—20 karat
  • 750—18 karat: Typical fineness for modern jewelry in most of Europe. Even in regions where higher purities are common, this is the maximum fineness used for gemstone-set jewelry, as the metal must be hard enough to robustly hold the stone in place.
  • 625—15 karat
  • 585—14 karat: Most common fineness for jewelry in the United States. While 14 karat is more precisely 583.3 fine, this level is not generally used in decimal fineness.
  • 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. It is also the minimum for Denmark, Greece and Mexico.
  • 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 silver bullion coins. Used in U.S. silver commemorative coins and silver proof coins starting in 2019.
  • 980: common standard used in Mexico ca. 1930–1945
  • 958: Britannia silver
  • 950: French 1st Standard
  • 947.9: 91 zolotnik Russian silver
  • 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. The standard used for English coinage from the time of Edward I until 1920. Widely used in the manufacture of silver items, including flatware, jewelry, musical instruments, home decor, etc.
  • 917: a standard used for minting Indian silver, during the British raj and for some coins during the first Brazilian Republic.
  • 916: 88 zolotnik Russian silver
  • 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 proof coins 1982–2018. Also used in coins from Spain, Russia, China, Argentina, Germany, Switzerland, Italy, Yugoslavia, Czechoslovakia, Hungary, Japan, Egypt, Turkey, Lebanon, Israel, and Panama. Commonly used in American cutlery before about 1870
  • 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
  • 875: 84 zolotnik is the most common fineness for Russian silver. Swiss standard, commonly used for export watchcases. Also used in silver from the Baltic States, Finland, Poland, Switzerland, and Romania. Commonly found in jewelry and other silver items produced in the Soviet Union.
  • 868: 83 zolotnik. Imperial Russian coinage between 1797 and 1885.
  • 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 ; Egyptian silver; Canadian silver circulating coinage from 1920 to 1966/7 Used for the outer cladding of US half dollars between 1965 and 1970, and commemorative issue Eisenhower dollars between 1971 and 1978
  • 750: An uncommon silver standard found in older German, Swiss and Austro-Hungarian silver
  • 720: Decoplata: many Mexican and Dutch silver coins use this standard, as well as some coins from Portugal's former colonies, Japan, Uruguay, Ecuador, Egypt, and Morocco.
  • 600: Used in some examples of postwar Japanese coins, such as the 1957-1966 100 yen coin
  • 500: Standard used for British coinage 1920–1946 as well as Canadian circulating coins from 1967 to 1968 and commemoratives from 1971 to 1991 and some coins from Colombia and Brazil. Also used on some Peruvian and Soviet coins of the 1920s and 30s. Large Panamanian 20 balboas coins were also minted at this fineness from 1980 to 1985
  • 350: Standard used for US Jefferson "war nickels" minted between 1942 and 1945.
  • 100: Used for Mexican pesos 1957-1967

    Carat

The carat or karat 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

where
24-carat gold is pure, 18-carat gold is 18 parts gold, 6 parts another metal, 12-carat gold is 12 parts gold, and so forth.
In Britain, the carat was divisible into four grains, and the grain was divisible into four quarts. For example, a gold alloy of fineness 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
  • 75.00–79.16% = 18 c
  • 91.66–95.83% = 22 c
  • 95.83–99.95% = 23 c
  • 99.95–100% = 24 c

    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, 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.