Includes all proof coins for 2006; the cent, nickel, dime, quarter, half dollar, and dollar. 2006 also comes with all 5 state quarters minted that year. Your purchase comes packaged in the original US Mint Proof Set Packaging complete with a certificate of authenticity.

Proof Coins are extraordinarily brilliant with sharp relief and a mirror-like background. The proofing process results in coins that feature frosted, sculpted foregrounds, giving them a "cameo" appearance. Proof blanks are specially treated, polished and cleaned to ensure high-quality strikes. The blanks are then fed into presses fitted with hand-polished dies and struck at least two times to ensure sharp, high relief. The coins are then packaged in presentation cases to showcase and maintain their exceptional finish.

History of 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). Many countries now issue them.

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.

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.

The U.S. largely stopped striking proof coins in 1916, although a few later specimens exist. Beginning in 1936, the U.S Mint began producing proof sets. Sets struck from 1936-42 and, when resumed, from 1950-72 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.
source: wikipedia

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