When Coin Making Goes Awry

During the coin minting process, errors can occur at every step in the process.  Often these error coins make it all the way to circulation where a person may be lucky enough to find one in their spare change.

There are several ways in which an error coin is produced.  Most error coins are the result of an accident or an equipment malfunction. Errors also occur  when the striking equipment begins to deteriorate, indicating it needs to be replaced. Finally, errors can occur if mint personnel make slight changes to the process in hopes of improving a coins quality. Sometimes this works and other times it fails, thus creating an error coin.

Here is a list of common errors:

  1. Blank Planchet:  Occurs after a coin blank has been turned into a planchet, but some how skips the striking process, resulting in a coin with no design. Blank_planchets
  2. Clipped Planchet: If the metal strip that is used to stamp out the coin blanks is misfed through the machine, it can cause the machine to punch down a second time on a blank.  This results in a chunk of the coin being cut out. Clipped_planchet
  3. Double Die: Sometimes an image is accidentally stamped twice on a coin, making part of it (usually the text) appear slightly blurry.  Double Die errors are arguably the most popular type of error coin. 1995_DDO_LIB_-_Copy
  4. Off Center Coins:  If a blank planchet gets out of place on its way through the striking process it is possible that it will only receive part of its image.  The other part of the coin will be blank, causing the image to appear off center. Off-center_strike
  5. Broad Strike: During the striking process coins are held in place using a collar which helps give the coin a nice, uniform rim.  If a coin does not get placed in a collar prior to being struck, it may spread out a bit and make the rim look funny.  This results in a coin that is wider than it should be and may or may not have a rim at all.   See how the below penny is just as big as the nickel beside it?  Broad_strike
  6. Overdate or over mint mark: Not everyone considers an overdate to be an error coin, but they are interesting. In the past, rather than creating new dies (stamps used to press the image on a coin), the mint just modified existing ones to include a new date or mint mark over the old one. If this modification was not done perfectly, it would result in the appearance of both dates or mint on the struck coin.

Depending on the type of error, these coins can be very valuable.  The 1955 Double Die Lincoln cent is worth up to $1000.  Many off center coins can be worth hundreds.  Broad strikes are also fairly valuable ranging in price from $20 to $200.  Value, like with all coins, is based on rarity and condition.

This list is only the tip of the iceberg when it comes to error coins.  Errors can occur at anytime and for a variety of reasons .  Although an error coin may be bad news to mint personnel, it is good news for collectors, proving once again that one man’s trash is another man’s treasure.



How Coins are Made

Coins are everywhere.  In fact, I’m willing to bet there are some hiding inside or under the couch or chair you are sitting in right now.  Have you ever stopped to think about how these round pieces of metal we absentmindedly set on top of our dresser , lose in the couch, or stash in a jar for a rainy day come to be?

The process can be explained in 7 steps:

  1. Blanking: In the United States, coins are minted in one of 4 cities (Denver, Philadelphia, San Francisco, and West Point).   Sheets of metal measuring 13 inches wide and 1500 feet long are rolled into coils.  These coils are fed through a blanking press, which is basically a large cookie cutter that punches out coin sized discs that are blank.


    Photo: Pat Loeb via CBS Loca

  2. Heating and Washing:  The blank coins are heated to 1500 degrees fahrenheit  in a furnace to make them soft.  They are then washed and dried.
  3. Riddling: The blanks get run through a “riddler” that pulls out any that are the wrong size.
  4. Upsetting: The coins that pass the size and shape test are run through an “upsetting” mill which gives each blank a raised rim.  Once a blank has made it to this point in the process, it is called a planchet. 

    By Dqfn13 (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], 

  5. Striking: The planchets are now are ready to become coins.  Large stamps  (called dies) give them the proper design and inscription to make them an official US coins. dies-for-gold-proof
  6. Inspection: The newly minted coins are spot checked for any blemishes or striking errors.  They are once again run through a sizer which gets rid of any bent or dented coins.
  7. Bagging and dispersing: The coins are counted (via machine) into large canvas bags, loaded onto pallets and shipped to the federal reserve. The reserve banks send them to your local banks where they are dispersed to local stores and eventually end up in your pocket or under your couch cushions.

Coins being counted and bagged

All the U.S Mint locations provide tours so you can see this process first hand. In the event that you are unable to make it to one of these facilities in your lifetime, do not worry!  The U.S mint has provided a virtual tour on their website.

Today, the equipment they use to make coins can pump out up to 75 million coins in a 24 hour period.  That’s a lot of coins and explains why they can be found almost everywhere! Next time you empty your pockets, or lift up your couch cushions take a closer look at those coins you find and consider all the work that went in to their creation.

Stay tuned next week when we talk about what happens when this process goes awry and error coins are produced!



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