1955 Double Die Cent
In 1955 something unusual happened at the Philadelphia Mint. During the process of preparing the working dies that were to be used for striking Lincoln cents, an error occurred. Working dies are made from steel blanks that receive several impressions from a master die (or hub as it is called). During one of these impressions, a slight misalignment occurred causing the die with Lincoln's portrait to have a doubling of the numbers and letters.
The error was discovered by mint employees after about 40,000 pieces were produced. Since about 24,000 pieces were already mixed in with normal cents, it was decided that these would be released. The remaining error coins were destroyed. Mint employees assumed that the error would never be noticed.
The double-dies first appeared in Upstate New York near the end of 1955 and caused quite a sensation. At first they traded for around 25c, but as news of their existence got around, prices went up quickly to $10 and more. Usually, an error coin will not cause such a stir, but the doubled impression on these coins was obvious, and they became very popular with collectors. Soon the variety was listed in the The Official Red Book: A Guide Book of U.S. Coins and its continued popularity was assured.
A 1955 Double Die cent is worth at least $500, and in uncirculated condition it could be worth from $1000 to $15,000.