Ron Guth:
The 121 Quarter Eagle in Proof condition is a great rarity, with only about four or five examples known. Since 1980, only five auctions contained a Proof 1821 Quarter Eagle, and at least one of those is a confirmed duplication. The last time one of these Proofs appeared at auction was in 2007, when a PCGS PR64CAM sold for $241,500.
The difference in appearance between Proof and Mint State versions of this date is dramatic, particularly in the area of strike. Most of the coins made for use in circulation have flatness on the stars, the high points, Liberty's hair, and on some of the eagle's feathers. Not so with the Proofs, which all show sharp star, hair, and feather detail. No documentation exists to explain the reason for striking Proof Quarter Eagles in 1821.