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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. 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 US 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, not the coins), 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.
See also Commemorative Coins
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