The 1943 copper-alloy cent is rare because, due to rationing for World War II, the vast majority of pennies struck that year were made of zinc-coated steel. The American Numismatic Association reports less than 50 of the 1943 copper-alloy cents are known to exist, according to the U.S. Mint.
The first recorded sale of a 1943 copper cent was for $40,000 in 1958, as reported by the U.S. Mint.
Although the exact origin of the coin has not been determined, the likeliest scenario is that copper-alloy 1-cent blanks remained in the press hopper when production began on the new steel pennies, which resulted in just a few pressings of the nonsteel pennies.
A magnet is used to verify if a 1943 penny is one of the rare copper-alloy cents. If the coin is attracted by the magnet, then it is made of zinc-coated steel and is not the rare penny.