lustre

OBS: Mint lustre or bloom is somewhat frosty in appearance as opposed to the mirror-like smoothness of the field of a proof. Since the lustre of a coin can vary considerably due to factors such as wear, polishing of dies or blanks, exposure to chemicals, humidity, or temperature extremes, etc., it is an important indicator of the condition or grade of a coin. The qualities of lustre are often described by such adjectives as fiery, frosty, light frost, heavy frost, satiny, flat looking, matte, semi-matte, and so on. Although normally brilliant, with time, lustre may become dull, spotted, or discoloured. Lustre is easily worn through with the slightest amount of circulation and strong chemical cleaners will destroy it. Once the mint lustre is gone it cannot be properly restored.