A proof coin is one that is struck with specially constructed dies. These coins are struck more than once to produce a high level of detail. When the coin is struck with these highly-polished dies, under significantly greater pressure than normal, the metal is forced into all the crevices of the mold creating the intricate design. At the same time the coin is struck, an acid is applied to the die that creates a satin finish to parts of the coin. Usually, the high relief of the coin is satin or matte finish and the background of the coin is shiny. The finished proofs are removed from the dies with tongs or by hand with gloves. After striking, the proofs are usually packaged in clear hard acid-free plastic. These cases assure that the coins are safe from handling and moisture, and will retain their value.
The United States mints these proof coins for collectors and usually sells them in sets. They are generally eagerly anticipated by collectors. A typical proof set might include an example of each coin made for general circulation for a given year. This would include a penny, nickel, dime, quarter and half-dollar. Some specialty proof sets have also been minted over the years. One such set is of the Statehood Quarters set, with one state's quarter minted during a certain year. These sets were minted in clad metal and also in 90% silver versions. The state quarters program has proven to be very popular with casual collectors, as well as more experienced coin buffs. Other specialty sets include dollar coins and half-dollar coins.
The first proof sets were available from the U.S. Mint in 1936. Although these coins contain the same amount of precious metal as circulated coins, they are sold at a higher price to help cover the added time and care of their production. Many collectors feel that these specially created set are well worth the extra cost, and take great pains to collect and preserve these proof sets.
During World War II, in the years 1943 through 1949, no proof sets were minted. The metals were needed in the war efforts instead. Again in 1965, 1966 and 1967 no proof sets were produced, although Special Mint Sets were sold.
Mint sets can be confused with proof sets. Both are uncirculated, but the mint set does not have the high sheen and great detail of the proof set. Mint sets are generally much more affordable than proof sets, and a great way for beginners to get involved in collecting uncirculated sets.
To start on your proof or mint set collections, a great resource is the website for the Washington Mint. Here you can find a catalog of current sets available for sale, as well as specifics on US proof sets, US mint sets, US state quarter sets, US silver dollars, and a range of other US and foreign coins.
Some of the more popular proof sets in recent years are the Sacagawea Dollar, the Westward Journey Nickel Series, and the annual Mint Silver proof sets from the Washington Mint. The Washington Mint site also offers an online registration to put your name on the waiting list for upcoming proof sets. This is a great way to be assured that you will get the proof sets you want, and at the fair market price.
You can also find proof sets at online or local coin dealers, or visit a coin convention or trade show. Be sure to do your homework before you buy, so you know what you are looking for and how much you should expect to pay.