Earlier this month error dealer Jon Sullivan published a nice article on the PCGS site about double-struck error coins. Here's an excerpt - see the complete article online.
A very popular mint error type is the double-strike. It is dramatic in appearance and easily understood. Some of the most valuable mint errors are double-struck coins. Double-strikes are found on the earliest ancient coins all the way up to the modern-day coinage. Because of how coins are made, being
struck with dies, it's an error type which will likely always be with us (and that's a good thing!)
As the name would suggest, a double-strike is a coin that is struck
twice. The double-struck coin typically will be struck correctly on the first strike, but then will be struck again either on-center or off-center. A double-struck coin is one that has just been struck twice, but the number of times a coin can be struck is infinite, and some coins are known with over 100 strikes on them.
Let's talk about the four primary double-struck types: the double-struck off-center, the double-struck on-center, the multi-struck, and the flip-over double-struck.
A double-struck off-center coin is one of the most common types of double-struck errors
The double-struck off-center occurs when a coin is struck and then fails to be fully ejected from between the dies before being struck a second time with the strike off-center. Above, we see an example of a double-strike with the second strike off-center. This is the most common of the double-strike types.
The double-struck on center shows the second strike virtually on top of the primary strike
Double-strikes on-center generally occur when a coin is struck, fails to be ejected from the collar die, and is struck again with the second strike directly on top of the first strike. Oftentimes, double-strikes on-center will be rotated between strikes, with the first strike not perfectly aligned with the second strike.
A multi-strike is a coin with three or more strikes. Multi-strikes can be either on-center or they can be off-center, but in order to qualify as a multi-strike, the coin must have at least three strikes present. It is not uncommon for a coin to be struck four or five or more times, although generally the more strikes a coin has the scarcer it will be.
Why do double-strikes occur at all? Usually, it's because there is something not working correctly with the coin press' ejection system, and the feeder finger (which is what puts planchets between the dies and ejects them from the die) is not working correctly; it fails to eject the struck coin from between the dies. When this happens, the dies strike the coin a second, third, or more times until either the coin is ejected or a mint employee notices the press is not functioning properly, stops the press, and fixes whatever the issue is.
To read the complete article, see:
Double-Struck Mint Errors
Wayne Homren, Editor
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