Proof coins were initially used for checking the quality of the dies used for minting. The process of creating the proof coin involves highly polished dies that are chemically treated to help bring out a frosted finish. The coins are double struck to create a highly detailed coin with a mirror finish and sharper rims. When grading these coins the quality of the strike, the centering of the image, and other aspects that show the quality or deficiency of the coin is considered. The highest grade possible for a proof coin is PR70. Watch the video on this page to see how the process of making these coins.