Proof coinage

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). Nearly all countries have issued proof coinage.

Preparation of a proof striking usually involved polishing of the dies. They can usually be distinguished from normal circulation coins by their sharper rims and design, as well as much smoother "fields" – the blank areas not part of the coin's design.

The dies for making modern proof coins are often treated with chemicals to make certain parts of the design take on a frosted appearance, with the polished 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 19th century even appear to be scratched, but it was part of the production process. The term "proof" refers to the process by which the coins are made and not to the condition of the coin. Certification agencies can grade and assign numerical ratings for proof coins. A PR70 coin is the highest grade possible for a proof coin and indicates a perfect example, with PR69 and lower grades reflecting some deficiency in the strike, centering, details, or other aspect of the coin.

Most proof coins are double struck under higher pressure. This does not normally result in doubling that is readily observable, but does result in the devices being struck fully. After being struck, they are separately and individually handled, in contrast to normal coins which are thrown into bins.

The U.S. had largely stopped striking proof coins in 1916, although a few later specimens exist. Beginning in 1936, the U.S. Mint began producing proof coins again. Proof coins through 1942 could be ordered individually from the mint. Because of this the lowest mintage for any denomination (cent through half dollar) determines the total number of complete sets that can exist. Consequently, this number is used to indicate the mintages of proof sets for the years 1936 through 1942. Beginning in 1950 customers could order proofs coins only as complete sets, although coins were packaged as sets rather than individual coins beginning only in 1955, when the U.S. Mint sold both individually packaged coins in boxes and sealed "flat pack" sets of coins.

Sets struck from 1936 to 1942 (1942 offered a five-coin and a six-coin version, the latter included the silver wartime nickel) and, when resumed, from 1950 to 72 include the cent, nickel, dime, quarter, and half dollar. From 1973 through 1981 the dollar was also included, and also from 2000 on. From 1950 to 1955, proof sets were packaged in a box and each of the five coins was sealed in a cellophane bag. 1955 saw both the original "box" packaging and introduced the flat-pack, where the coins were sealed in cellophane and presented in an envelope. The flat-pack packaging continued through 1964, after which the coins were sealed in various styles of hard plasticized cases. (From 1965 to 1967 the production of proof sets was suspended and Special Mint Sets were made in their place. They were made at the San Francisco Assay Office but bore no "S" mintmark.)

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