Katherine Mullen's blogs on coin collecting basics.

3 minutes reading time (514 words)

How Do Coin Errors Occur during Minting?

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Those unfamiliar with the ins and outs of coin collecting may be surprised to learn that coin errors - mistakes made when coins are minted - often enhance rather than detract from the value of said coin. While flaws that decrease a coin’s attractiveness can also decrease its value, error coins, or flawed coins made in the mint during the coin-making process, are also rare. This is because minting defects happen rarely, particularly with the advent of modern technology. Additionally, most error coins are detected before they are issued into the coinage, and they are recycled and remade in their proper form.

In order to understand why errors occur, it’s useful to understand how coin minting has been done historically and is done now. Here’s a fun primer from the U.S. Mint. A problem in each step of the minting results in a different type of coin error. Here are some of the most common types:

Off center strike - Off center strikes are the most frequent type of coin error; they occur when the coin blank or planchet does not land correctly on the collar (a circular piece of steel that acts as the wall of the coining chamber) and the die only strikes part of it. Off center strikes can be off center by any percentage; coins that are 10% off center will show most of their design while coins that are 90% off center will hardly look like the coins they are supposed to be at all.

Broad strikes - Broad strike mint errors that happen when the coin is stuck without a collar. This means the metal is allowed to expand in diameter and they appear fatter than they should be. Broad struck coins can be centered or off center, but all the detail of the coin’s design must be present.

Double strikes - Double strikes are coins that did not eject from the collar when they were supposed to and so the die struck them more than once, creating a double impression of the coin on the planchet.

Partial collar strikes - Partial collar strikes occur when the collar does not fully hold the edge of the coin blank. This results in a malformed rim, the most common of which is a circular line that fades away on part of the coin, although if the coin has edge reeding, it can look more like railroad tracks.

Indents - Indented coin error happen when two planchets are placed in one collar and the one on top is improperly placed. When the die strikes, then it creates a depression the shape of the top planchet on the coin below it.

There are any number of coins errors, but how they occur isn’t difficult to understand once you have a grasp on how coins are minted. Whether because of mechanical or human error, mistakes do occur, but they are not always a bad thing for a coin collector with a preference for the out of the ordinary. In fact, for many a coin collector, error coins make for an exciting treasure hunt!

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