Charles R. writes: My friend told me my 1979-D Washington quarter looks like it may be a double die. What does that mean?
There are many working dies that are made for each year’s coinage. Each die has a life of about 100,000 coins and there are many coin presses working at once. About one billion quarters or more are minted each year requiring quite a few working dies.
Doubled dies are created when in the process of manufacture, the potential working die rotates during one or more blows from the master hub. In reality, tiny but detectable amounts of doubling are common. Collectors are looking for obvious doubling where a good deal of rotation occured in the manufacture of that specific die. Usually, gross errors are caught by the Mint workmen but not always. Look at the severe die error in the 1955 doubled die cent. These even escaped detection after they were struck and many of these spectacular errors ended up in circulation before anyone at the Mint detected the error.
Note that every coin stuck with the defective die exhibits the exact same error. Don’t confuse double die errors with mechanical errors such as “shelf” doubling caused by a loose collar that hold a coin blank in place as it is struck. Each of these is unique and though doubling is present, has a different “look” than those from a doubled die.