An error coin is a coin that was not correctly made during its manufacture and is outside of acceptable tolerance limits. Error coins may have problems such as being struck off-center, having the wrong planchet type, having the planchets improperly produced so they are too thick, thin, improperly claded, or any number of other problems that occur during coin manufacturing.
Mint errors should not be confused with die varieties, which are coins that bear differences on their surfaces as a result of variations in the dies used to strike them, such as the way dates and mint marks were punched, or features that were doubled during die creation, etc. The major determining factor between error coins and die varieties is that die varieties are reproduced hundreds or thousands of times because the imperfection was on the coin die used to produce the coins.
Classification of Error Coins
There are three different classifications of error coins. Some error coins may have a combination of these problems.
Types of Mint Errors
- Die Cap - Occurs when a planchet is fed into the coining press, the previous planchet did not eject and the first planchet sticks to one of the coin dies. After repeated strikes, the first planchet starts taking the form of a bottle cap.
- Wrong Planchet - The incorrect planchet is fed into the coining press and does not match the dies that are loaded in the press.
- Off-Centers - The planchet is not centered between the two coin dies in the coining press.
- Broadstrikes - The coining collar that holds the coin between the two dyes is not fully engaged in the coin is struck anyway.
- Partial Collars - The coining collar is partially engaged in results in a malformed coin edge.
- Brockages - One coin is struck on top of another coin in the coining chamber.
- Double & Triple Struck - The coin is struck multiple times.
- Die Adjustment - The coin is struck with not enough pressure due to the coin press operator adjusting the machine.
- Bonded Coins - Two coins are struck together.
- Double Denominations - A coin is first struck with one denomination and then fed through a coining press that has coin dies for a different denomination.
- Coins Struck on Feeder Finger Tips - The coin press uses "feeder fingers" to feed the planchets into the coining press. Occasionally, the feeder finger gets struck with the coin design instead of the planchet.
- Struck Fragments - Metal fragments from various sources can end up in the coining press and get struck with the coin design.
- Proof Errors - Any proof coin that was not properly prepared according to proof coin standards.
- Transitional Errors - When the mint changes from one metallic composition to another and a previous planchet with the old composition ends up getting struck as a new dated coins.
- Fold-Over Strikes - A planchet is fed into the coining press in the vertical position and get struck on its edge instead of on its surface.
- Missing Edge Lettering - Coins that are supposed to have lettering on the edge is missing. This is most prevalent on Presidential Dollars.
The Official Price Guide to Mint Errors
Although error coins are very difficult to price and a definitive price guide for coin errors does not exist, Alan Herbert authored The Official Price Guide to Mint Errors. The seventh and last edition was published in 2007 before Herbert died in January 2013. The book does an excellent job of creating a cataloging system for mint errors.
In order to completely understand error coins, you must first understand the minting process. Herbert does an excellent job of presenting the minting process in Chapter 2. He dives deep into the minting process for modern coins as well as classic United States coins. The following chapters detail each and every category of error that can happen. This follows the PDS (Planchet, Die, Strike) system for cataloging the different types of coin errors that can occur.
For each type of coin error, Alan lists relative rarity level, a value between 1 and 8 (1 being very common and 8 being extremely rare), and a value range based upon current market conditions. He makes it very clear that the value of an error coin can only be determined when you go to sell it.
Edited by: James Bucki