The physical specifications of U.S. coins—metallic content, weights, diameters—have been ever changing. Changes were in response to increases and decreases in metal prices, public rejection of large-diameter coins, and other factors.
Even before the first copper coins were struck in 1793, their weights were reduced under the Act of May 8, 1792. The modified weights are 6.74 grams for the half cent and 13.48 grams for the cent (weights are given in grams for modern convenience; the early coinage laws specified the weights in grains). Weights for both copper coins were reduced in 1795, to 5.44 grams for the half cent and to 10.89 grams for the cent. The 1794 and 1795 silver coinage was struck in a composition of 90 percent silver and 10 percent copper, according to some sources. When additional silver denominations were added in 1796, the composition for all five coins was changed to 89.2427 percent silver and 10.7572 percent copper, until additional change came in 1836 and 1837.
Composition of the first gold coins is 91.6667 percent gold and 8.3333 percent copper and silver.
The only changes made to U.S. coins from the first decade of the 19th century to 1834 were to the designs. Then, on June 28, 1834, the weight of gold coins was reduced and the alloy changed for two years to 89.9225 percent gold and 10.0775 percent copper and silver. In 1836, the gold alloy was changed again, to 90 percent gold and 10 percent copper and silver, an alloy unchanged until 1873. Changes were made to silver coins in 1836 as well, when the silver content was changed to 90 percent silver and 10 percent copper, an alloy used until the mid-1960s.
The rising price of silver resulted in a reduction in weights for the silver coins during 1853 (except for the silver dollar). Arrows were added to both sides of the dates on the reduced weight half dimes, dimes, quarter dollars and half dollars, a design feature used for 1853 and 1854. The arrows were removed in 1855 although the weights of the coins remained the same.
Major changes were made to the country’s copper coinage in 1857. The half cent was eliminated and the large copper cent was replaced with a smaller cent composed of 88 percent copper and 12 percent nickel (Act of Feb. 21, 1857). Diameter of the old cent is approximately 29 millimeters; the new cent has a diameter of 19 millimeters. A bronze cent and 2-cent coin were introduced in 1864.
The weights of the Seated Liberty silver coinage were increased in 1873, and once again arrows were placed at either side of the date to signify the increased weight. Also, silver was dropped from the gold-coin alloy, which was changed to 90 percent gold and 10 percent copper.
The next major compositional changes in U.S. coins were made during World War II. At the beginning of the United States’ entry into World War II, several metals used in coinage became strategically important to the war effort. The first to be affected was the 5-cent coin, which had nickel removed starting Oct. 8, 1942, when 5-cent coins in a new composition—56 percent copper, 35 percent silver and 9 percent manganese—went into production. Use of the copper-nickel alloy was resumed in 1946.
Also during the war, the cent composition was changed. First, tin was removed sometime late in 1942. Then, in 1943, a zinc-coated steel cent was introduced to conserve copper. The brass alloy of 95 percent copper and 5 percent zinc resumed in 1944 through 1946. The 95 percent copper, 5 percent tin and zinc composition resumed in 1947 and continued until late 1962 when, once again, tin was removed from the bronze alloy, returning the alloy to the same composition, called brass, used in 1944 to 1946.
The 175-year-old history of United States coinage was changed with the stroke of a pen on July 23, 1965. On that day President Lyndon Johnson signed into law the Coinage Act of 1965, representing the most sweeping changes to the U.S. coinage system since the Mint Act of 1873. The 1965 act eliminated silver in dimes and quarter dollars and reduced the silver content of the half dollars to 40 percent.
Special congressional hearings relative to the nationwide coin shortage were first held in 1964. Coin shortages had continually worsened in the decade prior to 1965 as a result of the population growth, expanding vending machine businesses, popularity of Kennedy half dollars and the worldwide silver shortage. In the face of the silver shortage, it was essential that dependence on silver for coinage be reduced. Otherwise the country would be faced with a chronic coin shortage.
As a result of studies conducted by both the Treasury and the Battelle Memorial Institute, a clad metal composed of three bonded layers of metal was selected for the new composition. Battelle tested various alloys to determine their suitability for coinage. (Battelle is a Columbus, Ohio-based company that specializes in high-tech experimentation and research.) The dimes and quarter dollars were composed of two layers of 75 percent copper and 25 percent nickel bonded to a core of pure copper. The half dollars were composed of two layers of 80 percent silver and 20 percent copper bonded to a core of approximately 20 percent silver and 80 percent copper; the entire coin is composed of 40 percent silver.
The combination of copper-nickel and copper gave the new dimes and quarter dollars the required electrical conductivity, a necessary property for vending machines. The copper-nickel surfaces also continued the traditional silvery color of the coins.
The legal weights of the coins were affected by the change in alloy. The new dime weight is 2.27 grams, the quarter dollar weighs 5.67 grams and the 40 percent silver half dollar weighs 11.5 grams. With the elimination of silver from half dollars in 1971 and the introduction of a copper-nickel clad version, the weight was changed to 11.34 grams. The cladding of all coins constitutes approximately 30 percent of the coin by weight.
In an effort to maximize coin production during the transition to the new alloys, 1964-dated silver coins were struck into 1965. The Coinage Act of 1965 also made it mandatory that clad coins be dated no earlier than 1965. All clad coins actually made in 1965 bear that date. The first copper-nickel clad dimes were struck in late December 1965 and were released March 8, 1966. The first copper-nickel clad quarter dollars were struck Aug. 23, 1965, and released Nov. 1, 1965. The first silver-clad half dollars were released March 8, 1966, but were struck starting Dec. 30, 1965. The 1965 date was retained until July 31, 1966, when the date was changed to 1966. Normal dating resumed Jan. 1, 1967.
Another great compositional change to U.S. circulating coinage came in mid-1982, when the brass cent was replaced with a cent of nearly pure zinc, plated with a thin layer of pure copper to retain its copper appearance, in reaction to rising copper prices.
When the American Eagle bullion coins were introduced in 1986, some numismatists were critical of the .9167 gold content, a composition they deemed “nontraditional”; there was some preference for a .900 gold content. However, the chosen composition is virtually identical to the alloy first used for U.S. gold coins, from 1795 to 1834. A new silver composition was introduced with the production of the .999 fine silver American Eagle dollar.
The Treasury secretary now has authority under a change in the law in 1992 to change the composition of the American Eagle gold coin without seeking congressional approval. The 2009 Saint-Gaudens, Ultra High Relief $20 gold double eagle, composed of .9999 fine gold, was issued under this authority. The American Buffalo .9999 fine gold bullion coins were ordered into production by Congress, however.
The platinum American Eagle bullion coins, introduced in 1997, are .9995 fine.
Mint officials experimented with ringed-bimetallic pieces in early 1993. The coins—consisting of an outer ring of one metal bonded to an inner ring of another, different-colored metal—are being used in circulation by many countries.
The introduction of the 2000 “golden” dollar depicting Sacagawea resulted in another new alloy. U.S. Mint officials selected a composition that has two outer layers composed of manganese-bronze (77 percent copper, 12 percent zinc, 7 manganese and 4 percent nickel) bonded to an inner core of pure copper. Overall, the total composition is 88.5 percent copper, 6 percent zinc, 3.5 percent manganese and 2 percent nickel. The same alloy is used in the Presidential dollars and Native American dollars.
The American Eagle 1-ounce .999 fine silver bullion coin was joined in 2010 by the America the Beautiful 5-ounce .9999 fine silver bullion coin. The America the Beautiful 5-ounce coin is 3 inches in diameter and is both the heaviest and largest-diameter U.S. coin ever issued.