United States Mint Proof sets have extraordinary brilliant coins that have sharp relief and mirror-like backgrounds. The term Proof refers to the method of manufacture and not the condition of a coin. Proof coins have frosted sculpted foregrounds that give them a special cameo effect. Proof coins are struck on blanks that have been specially treated, polished and cleaned to ensure a high quality strike. The blanks are fed into presses fitted with hand-polished dies and are struck at least twice under intense pressure to ensure a sharp proof finish. These Proof sets are then packed in presentation cases to showcase and maintain their exceptional finish. Many valuable treasures and important coins can still be found in proof sets.