Proof issues are minted to the highest standard using highly polished dyes to strike the coin. They are usually limited in edition, and often they are more costly than a standard strike. Proof coins are sometimes issued individually or as a set. Some of the older issues have vastly increased in value since their release. The more modern proof coins /sets come certificated, and often have a mirrored finish with a frosted portrait and reverse design. These exibit the ultimate strike and the best possible detail and they make fantastic collectors items.