The National Baseball Hall of Fame Commemorative $5 gold, $1 silver, and one-half dollar clad coins will have a shape such that the obverse is concave and the reverse is convex. While these will be the first curved coins ever minted by the United States Mint, it did produce the curved 1973 Roberto Walker Clemente Congressional Gold Medal in honor of the late Pittsburgh Pirates star right fielder.
The National Baseball Commemorative Coin Act specifically refers to modeling the coins after the convex/concave 2009 International Year of Astronomy Coins minted and issued by the Monnaie de Paris (French Mint). The United States Mint’s National Baseball Hall of Fame Commemorative $5 gold, the $1 silver and one-half dollar clad coins will also be closely modeled after the Royal Australian Mint’s Southern Cross curved coins.
Research and development on the curved National Baseball Hall of Fame Commemorative Coins is unprecedented in recent United States Mint history. It covered height of relief limitations; milling, turning and grinding operations; coinability issues; laser frosting and proof polishing; and proof, uncirculated and clad test strikes.
During the planning phase for the minting and production of its first-ever curved coins, the Royal Australian and Perth Mints provided valuable technical insight to the United States Mint.