By Coins Magazine posted on Numismaster
Grades listed are based on the following standards established by the American Numismatic Association. For more detailed descriptions, see Official ANA Grading Standards for United States Coins, by Ken Bressett and A. Kosoff (American Numismatic Association, 818 N. Cascade Ave., Colorado Springs, CO 80903-3279.

Proof Coins

The term “proof” refers to a manufacturing process that results in a special surface or finish on coins made for collectors. Most familiar are modern brilliant proofs. These coins are struck at the Mint by a special process. Carefully prepared dies, sharp in all features are made. Then the flat surfaces of the dies are given a high, mirrorlike polish. Specially prepared planchets are fed into low-speed coining presses. Each proof coin is slowly and carefully struck more than once to accentuate details. When striking is completed, the coin is taken from the dies with care and not allowed to come into contact with other pieces. The result is a coin with a mirrorlike surface. The piece is then grouped together with other denominations in a set and offered for sale to collectors.

From 1817 through 1857, proof coins were made only on special occasions and not for general sale to collectors. They were made available to visiting foreign dignitaries, government officials, and those with connections at the Mint. Earlier (pre-1817) U.S. coins may have prooflike surfaces and many proof characteristics (1796 silver coins are good examples), but they were not specifically or intentionally struck as proofs. These are sometimes designated as “specimen strikings.” Read Full Article