Proof Sets

Proof coinage means special early samples of a coin issue, historically made for checking the dies and for archival purposes, but nowadays often struck in greater numbers specially for coin collectors (numismatists). more...

They can usually be distinguished from normal circulation coins by their sharper rims and design, as well as much smoother fields.

Preparation of a proof striking usually involved polishing of the dies. Modern U.S. proof coins are often treated with chemicals to make certain parts of the design take on a frosted appearance, and the fields taking on a mirror finish. Several other methods have been used in the past to achieve this effect, including sand blasting the dies, and matte proofs. Proof coins of the early 1800s even appear to be scratched, but it was part of the production process.

Most proof coins are double struck. This does not normally result in doubling that is readily observable, but does result in the devices being struck fully.

Beginning in 1936, the U.S Mint began producing proof sets. Sets struck from 1936 through 1972 include the cent, nickel, dime, quarter, and half dollar. From 1973 through 1981 the dollar was also included, and also from 2000 on. Regular proof sets from 1982 to 1998 contain the cent through the half dollar. Other sets, called Special Prestige sets, also contain commemorative coins. These sets were sold from 1983 to 1997 at an additional premium. Beginning in 1999, proof sets also contain five different statehood quarters.

Read more at Wikipedia.org