In 1968, the San Francisco Mint issued its first dazzling U.S. proof set, launching a magnificent new era in American coinage. U.S. proof sets had been briefly discontinued after the last Philadelphia issue of 1964. But since 1968 the exclusive San Francisco Mint U.S. proof sets have come to be regarded as the finest in American minting history. Each proof has double-struck, deep-sculpted engravings and mirror fields. Included are the cent, nickel, dime, quarter and half dollar in superlative proof quality. U.S. Mint case.