Errors, Varieties & Special Issues

Mint errors occur during the manufacturing process at the mint, creating unique, physical deviations from the standard coin design. These errors are grouped into three main families: planchet errors (such as clipped planchets, where a crescent-shaped piece of metal is missing, or lamination flaws where the metal splits), die errors (such as doubled dies, where the die itself was stamped twice during manufacturing, creating doubled lettering, or die cracks and cuds), and striking errors (such as off-center strikes, where the planchet was not aligned with the dies, or brockages, where an already-struck coin sticks to a die and presses its design into the next blank coin).

Mule coins are another popular variety, created when the obverse die of one coin type is accidentally paired with the reverse die of another type. These errors are highly prized by collectors due to their visual uniqueness and extreme rarity, with values determined by the dramatic nature of the error and the popularity of the host coin.

A common mistake among beginner collectors is misidentifying post-mint damage (PMD) as a rare mint error. PMD includes any wear, cuts, chemical corrosion, or deliberate alterations that occur after a coin leaves the minting facility. For example, coins that have been flattened by trains, squeezed in vises, or exposed to acid can look like clipped planchets or broadstrikes but are actually worthless damaged pieces.

To identify a genuine error, verify the coin's weight and edge details. A genuine clipped planchet will show a characteristic 'Blakesley effect'—a slight weakness in the rim details directly opposite the clip, caused by uneven metal flow during striking. If the rim details opposite the clip are perfectly formed, the clip is likely a private alteration made after the minting process.