Identifying Error Coins
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Identifying Error Coins

Steven Cochran
By Steven Cochran
Published June 01, 2010

Modern coin minting is a highly technological process. On occasion however, even the most advanced processes break down, and mistakes are made. These errors are usually caught at the Mint, and tossed into the scrap heap to be melted down.

When these error coins make it out into the world, however, they become sought-after prizes by coin collectors.

Error coins can be divided into three broad categories:

  1. Planchet Errors: where the coins blanks are made from defective material, or there were mistakes in cutting them out of the original metal strips;

  2. Die Errors: Mistakes or damage on the dies that are pressed into the coin blanks; and

  3. Striking Errors: Errors that occur during the coining process that are not a result of defective planchets or dies.

Planchet Errors: Coin blanks are cut from long metal strips that have been rolled to the correct thickness, then fed through the stamping press. After being stamped out, the blank metal disks are cleaned and run through the upsetting mill, which applies the rim. After this process, they are known as planchets, and are ready to be made into coins.

  • Clipped Planchets are created when the metal strip does not advance through the stamping press properly, leaving part of the hole of the previous punch in the striking area. This results in a blank with a crescent-shaped piece missing. If it gets through the entire coining process undetected, it is known as a "clipped coin".
  • Lamination and Cladding Errors: Cents, dimes and quarters are made from "clad" blanks. A copper core is sandwiched (clad) between two layers of copper-nickel alloy. Sometimes, impurities in the alloy can cause layers of the coin to delaminate, and begin peeling. Other times, the layers of copper-nickel alloy fail to bond with the copper core, and begin to separate.

Die Errors: Coin dies are the hardened steel cylinders that are engraved with the coin design in reverse relief. There are two dies: One with the design for the obverse (front) of the coin, and one with the design for the reverse (back) of the coin. The minting process involves these two dies being pressed together at high pressure, with a coin blank in the middle.

The extreme forces of the coining process can lead to die failure, especially during the 19th and early 20th centuries, when metallurgy was not as advanced.

  • Cracked Die: The first sign of die failure would be a crack in the die. The pressures of the coining process would force the metal of the coin blank into the crack, resulting in a raised ridge that followed the path of the crack. As the die damage increased,the crack would get larger, until there was a
  • Die Break: When a die finally failed, sometimes only a small piece of the die would break off. Because there was nothing in the gap to transfer a design, the area of a die break was a raised, flat area.

Other die errors aren't the result of mechanical failure. Rather, they were the product of the old, hands-on minting process of yesteryear.

  • Overdate: Coin dies were expensive and labor-intensive to make. Therefore, if there were dies that were still serviceable at the end of the year, the engraver would buff out the last digit of the year, and stamp a new digit over it for the new year. Sometimes, the old digit was not completely buffed out before the new one was hand-stamped over it. The old digit can still be faintly seen underneath the new digit on coins made from that die.
  • Repunched Mintmark: In the old days, all coin dies were made at the main US Mint in Philadelphia, then shipped to the branch Mints. The mintmark for the branch was hand-stamped onto the die. using a long punch. If the Mint employee didn't hit the punch hard enough, he had to repunch the mintmark. This never ended up in the exact same spot, which means that both strikes of the letter can be seen.
  • Overpunched Mintmark: Sometimes, the coin dies were sent to the wrong branch Mint, and the proper mintmark had to be punched over the old one. Unlike a repunched mintmark, there was usually some attempt to buff out the old mintmark before applying the new one. This makes many overpunched mintmarks nearly impossible to see without a magnifying glass.
  • Doubled Dies: The dies that are actually used to mint coins are known as "working dies". These are made by pressing a "hub" into heated steel. Sometimes the machinery would slip during this process, transferring the design onto the new die twice. Many times, it was hardly noticeable, but other times, such as the 1955 Doubled Die Obverse Lincoln Cent, it could be quite dramatic. Doubled Die error coins are some of the most expensive of all error coins. A doubled obverse die is abbreviated DDO for doubled die obverse; the reverse die is abbreviated DDR.

Strike Errors: Strike errors are caused by a flaw or malfunction in the coining procedure, instead of defects in either the dies or planchets. These types of errors usually self-correct or are caught sooner than die errors.

  • Broadstrike: This happens when the collar piece that surrounds the planchet during the striking process breaks or otherwise malfunctions. This allows the pressure from the obverse and reverse dies during the striking process to push metal beyond the normal diameter of the coin, making a "broader" coin.

  • Strike-Throughs: This occurs when debris is caught in the press during the coining process. A piece of cleaning rag caught between the dies might make a waffle texture on a portion of a coin. Hard items like nails and metal flakes will make sharp dents or valleys in a coin.

  • Brockage: Brockage errors usually result from a coin sticking to its die after the strike. When the next blank is fed into the press, one side is struck normally, but the stuck coin on the other side results in a concave, mirror image being struck on the other side. For example, if a coin sticks to the reverse die instead of being ejected from the coin press, the next coin will get the obverse struck as usual, but the obverse of the stuck coin is facing up from the reverse die and impresses a concave mirror image into the back of the coin.

  • Off-Center Strike: This occurs when the planchet fails to completely enter the striking area in the coining press. The part that isn't in the chamber has no design, obviously, and the design runs off the opposite edge. This is an obvious coin error, and can be quite dramatic.

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