Learn Grading: What Is a Mint Error? — Part 1

Every year, mints for major countries produce billions of coins. Despite sophisticated technology and comprehensive quality control efforts, some mistakes are made. Coins with mistakes are called “mint errors” and are among the most popular segments of numismatics.

In this series, NGC will explore mint errors and their causes. Part I focuses on the mint errors primarily caused by the dies used to strike the coins. Future articles will cover mint errors primarily related to the planchet and the strike.

Die-related Mint Errors

There are five types of mint errors that primarily relate to the die: Die Breaks, Misaligned Dies, Clashed Dies, Rotated Dies and Mules.

Die Breaks / Cuds: A die break occurs when a piece of the die breaks or chips off. This leaves a void in the die into which metal from the planchet flows during striking. As a result, there is a raised area without a design on the struck coin (called a “cud”). With die breaks, bigger is definitely better, and large cuds can be extremely valuable. Weakness can often be seen on the opposite side of a cud since the metal flowed into the void (instead of into the die as it normally would).

1985 India 10 Paise, Reverse Die Break, graded NGC Mint Error MS 65. (The die break is visible at 3 o’clock on the reverse, right.) Click images to enlarge.

Misaligned Dies: This error occurs when the dies are not properly aligned in the press. The result is a coin with one side that appears to be off center. However, the opposite side will be properly aligned.

1921-S Morgan Dollar with an Obverse Misaligned Die, graded NGC Mint Error XF 40. The obverse misalignment can be seen as the denticles nearly vanish on the left side of the coin, an issue not present on the reverse. Click images to enlarge.

Clashed Dies: Die clashes occur when the dies come together without a planchet between them. If the dies are incorrectly spaced, they can hit each other, transferring design elements from the obverse die to the reverse die and vice versa. This results in clash marks being struck onto coins that are subsequently minted by the die pair. These clash marks must be quite pronounced and unusual to be considered a mint error by NGC.

2017 Silver Eagle with heavy clash marks, most visible on the obverse. Click images to enlarge.

Rotated dies: All US Mint coins are struck with coin alignment. That is, when the coin is flipped from top to bottom, the reverse will be properly oriented. This is the opposite of medallic alignment, which has both the obverse and reverse oriented the same way. Rotated die errors tend to occur when a die is installed improperly or is loose and rotates on its own. It is much more common on early US Mint coinage. NGC will recognize rotated die mint errors only if there is at least 15 degrees of rotation.

2015-W High Relief Gold $100 graded NGC Mint Error MS 70. The notation on the label of MEDALLIC ALIGNMENT indicates the reverse of this coin is rotated about 180 degrees from where it should be. Click images to enlarge.

Mules: Mules are extremely rare and occur when two dies not meant to be paired together are used to strike a coin. If this mistake happens, the error coins are usually caught before they can leave the mint. The most famous and valuable recent mules feature a Washington Quarter obverse and a Sacagawea Dollar reverse (struck on a Sacagawea Dollar planchet in 2000). Examples sell for tens of thousands of dollars.

2000-P Sacagawea Dollar Muled With a Washington Quarter, Die Pair #1, graded NGC Mint Error MS 67. Click images to enlarge.

NGC attributes major mint errors under its Mint Error service for an additional fee. For more information about NGC Services & Fees, click here.

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