Proof coins are produced using special minting and processing techniques, resulting in coins with special finishes. They have been sold separately in the past, and since 1950, have been offered only in sets although Proof versions of recent commemorative coins, the American Ea...READ MORE
Proof coins are produced using special minting and processing techniques, resulting in coins with special finishes. They have been sold separately in the past, and since 1950, have been offered only in sets although Proof versions of recent commemorative coins, the American Eagle bullion coins, and the 1999 Anthony dollars have been offered individually.
While coins in Uncirculated Mint sets are little or no different from those struck for circulation, Proof coins are a special breed. A Proof coin is struck on specially prepared planchets, using special minting techniques, generally on a specialized coining press.
The term "Proof" means different things to many collectors, dealers and other hobbyists. Some believe Proof is the top level of preservation, or grade - it is not. Others believe Proof coins are particularly shiny coins destined for collectors rather than circulation - they are only partly correct.
"Proof" in numismatics refers to a special manufacturing process designed to result in coins of the highest quality produced especially for collectors. "Proof" is not a grade, as many beginning collectors think, although grading services, dealers and collectors may assign Proof coins numerical grades such as Proof 63 or Proof 65.
Proof coins result from the same basic processes used in producing the dies and planchets used in producing coins for circulation for use in commerce. However, Mint employees use special techniques in preparing the surfaces of the dies and planchets intended for Proof coins. Special presses and striking techniques are also used in the production of Proof coins.
Most of the Proof coins sold by the United States Mint today are Frosted Proofs. The flat fields are mirror-like, reflective and shiny. The frosting refers to the white, textured, non-reflective finish found on the raised devices, lettering and other points in relief. Both the frosted and mirror finishes are the results of the special techniques used in preparing the dies.
All dies are produced at the Philadelphia Mint and Denver Mint die shops, although the surfaces of Proof dies used at the San Francisco Mint are prepared in San Francisco. A die features a mirror image, incused version of the finished coins design. Points that are raised on the coin are incused on the die. Points incused on the coin are in relief on the die.
To prepare a Frosted Proof die, the die is first sandblasted with an aluminum oxide and glass bead compound. This imparts a rough, textured finish to the entire die. After the sandblasting is completed, cellophane tape is placed over the entire surface. The person preparing the die then removes the cellophane tape from around the incused areas in the die; in effect, the fields are uncovered and the cellophane protects the incused areas.
The uncovered surfaces are then polished to a high sheen while the textured finish on the incused areas is left intact. Once the polishing is completed, the die receives a light plating of chrome, two- to three-thousandths of an inch thick. The chrome is then buffed. The finished die now has mirror-like fields and textured relief, and will impart the same finishes to the coins it strikes.
The planchets used to strike the Proof coins also receive special treatment. The planchets are burnished in a process that tumbles them in a media of carbon steel balls, water and an alkaline soap. The process cleans and polishes the planchets. The burnished planchets are rinsed in clear water and towel-dried by hand, then go through another cleaning and hand-drying process. Compressed air is used to blow lint and dust from the planchets.
Proof coins are struck on special presses that operate at slower speeds than the high-speed presses used for striking circulating coinage. While the Proof coining presses, like all presses, impress the design from the dies onto the planchet, the product.