Proof coins are specially struck coins with special surfaces and strikes to bring out detail. Proofs can have a "matte" finish, achieved by sandblasting the dies and mirror-like finish by highly polishing the die. Early proof coins are rare as most were struck by special request or as presentation pieces. Regular production of proof sets began in 1936, although you can assemble sets of individual proof coins in prior years. Through the years, the number of coins has changed depending on which set you order. There some sets with silver quarters, some only presidential dollars. The United States Mint offers a dazzling array of proof sets in many different configurations.