What is an overstrike error on a 1941 or 1942 mercury dime?

Answer 1

An overstrike occurs when a coin that has already been minted is again impressed with dies bearing the features of a different coin. This practice took place in the years of the Roman Empire and also in Britain when silver became in short supply. The British took silver Spanish coins and stamped them with the image of the king and other features of the British coin. The US dime which bears both dates, 1941 and 1942, was not produced in this manner. A master die, called a hub, is used to make the actual dies which are placed in the presses to strike the coins. During the manufacture of these actual dies the design is stamped into them twice. After being stamped once they are then heat treated by a process called annealing. They are then returned to have the design of the coin stamped into them for the second time. In the case of the 1941 over 1942 dime, the dies were accidently switched and then stamped the second time with the master die [hub]. One master die was dated 1941, the other was dated 1942 so when the dies were finished they bore the dates of both master dies and the result was the 1941 over 1942 dime. The error was not noted right away at the mints and dimes bearing the error were placed into circulation. These dimes bearing no mint mark indicates they were struck at the Philadelphia mint but others carry the letter "D" indicating they were from the Denver mint.