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.