The cameo effect on a proof coin is produced by the field having a mirror-like surface and the coin's devices having a frosted surface. Proof coins minted before 1971 were made using a technique so that only the first hundred coins had a cameo contrast effect. If there is a dramatic contrast between the field and the devices, this is referred to as deep cameo.
Minting of Proof Coins
Some people think that "Proof" is a coin grade. Actually, Proof is a method of manufacturing high-quality coins for collectors. However, the amount of cameo contrast is graded. In order for a coin to qualify as Proof it must meet three basic criteria:
- The planchet must be specially prepared (cleaned and polished/burnished)
- The die that manufactures the proof coin receives special treatment in order to create high-quality coins
- When the coin is struck in the coining press, it must receive two or more blows to bring up the finest details of the coin's design.
Up until the mid-1970s, not all proof coins that were minted had a cameo contrast. The technology available to the mint at that time only allowed for the first 30 to 50 proof coins produced from a new set of dies to possess the deep cameo contrast. As the dies continued to be used to produce proof coins, the frosted surfaces of the devices became more mirror-like with each proof coin struck.
In the mid-1970s the United States Mint began experimenting with new technology that would enable every proof coin to receive a cameo contrast. After the proof die received its special treatment but before it was put into production, a coating was applied to the surface of the die that strengthened its surface and preserved the cameo contrast throughout its entire production run.
Some coins have an average contrast between the mirror-like surface of the field and a subdued frosted surface on its devices. Other proof coins have a dramatic contrast between the coin's highly mirrored field and the deep frosted relief on the devices. When the contrast between the field and the devices is so dramatic the coin is classified as a "deep cameo".
The production of coins involves metal dies striking metal planchets using several tons of force. Every time a coin is struck the die wears down and some of its detail worn away. As more and more proof coins are produced from a given set of dies the delicate frosted details on the dies start to wear off. This results in a less than dramatic cameo contrast.
Reverse Proof Coins
Most proof coins made for collectors have a cameo contrast where the fields of the coins have a mirror-like surface and the devices are frosted. Some proof coins have the mirror and the frosted surfaces reversed. In other words, the devices are mirror-like and the field of the coin is frosted.
The United States Mint made its first reverse proof coins and 2006. This included a $50 American Gold Eagle minted at the West Point mint and an American Silver Eagle minted at the Philadelphia mint facility. These were specifically made to commemorate the 20th Anniversary of the American Eagle Bullion Coin program.
Proof coins that have a cameo effect are highly prized by collectors.