Errors and Varieties
What counts as a genuine mint error versus a die variety versus post-mint damage, and a tour of the main types: off-center strikes, broadstrikes, clips, cuds, die cracks and clashes, doubled dies, repunched mintmarks, overdates, and the all-important doubled die vs. machine doubling.
Error or variety?
In plain English
An 'error' is a one-time machine mistake on a single coin. A 'variety' is a quirk cut into the die itself, so it shows up on every coin that die strikes. Same idea as a one-off slip versus a flaw in the mold.
Going deeper
The practical test: is the feature unique to this coin (error) or reproduced on others from the same die (variety)? Doubled dies, repunched mintmarks, and overdates are varieties; off-center strikes and broadstrikes are errors.
Sources: Professional Coin Grading Service (PCGS) · Numismatic Guaranty Company (NGC)
Error or just damage? (the crucial question)
In plain English
Before getting excited about an 'error,' make sure the oddity happened at the Mint and not afterward. Scratches, dents, and holes from later handling are post-mint damage, and they lower value rather than add it.
Going deeper
A mint error happens up to and including the final strike; anything after is post-mint damage (PMD). The strike leaves diagnostics, metal flow, luster, raised vs. incuse features, that reveal whether something is mint-made or later damage. PMD can even happen inside the Mint after striking, so 'made at the Mint' doesn't make it an error.
Sources: Professional Coin Grading Service (PCGS) · Numismatic Guaranty Company (NGC)
Striking and planchet errors
In plain English
Some errors come from how the coin was fed or struck, or from a bad blank: off-center strikes (design shoved to one side), broadstrikes (spread wide with no collar), clipped planchets (a piece missing), strike-throughs (an object blocked part of the design), laminations (metal peeling), and wrong-planchet coins (struck on the wrong blank).
Going deeper
Off-center vs. broadstrike turns on whether the full design is present; clips show the 'Blakesley effect' and struck edges that separate them from coins cut later; wrong-planchet coins are confirmed by weight, diameter, and composition.
Sources: Professional Coin Grading Service (PCGS) · Numismatic Guaranty Company (NGC) · Coin World
Evidence pages
Die errors: cracks, clashes, and cuds
In plain English
As dies fail they leave raised marks on coins: thin raised lines (die cracks), ghost images of the opposite side (die clashes), and blobs of metal where a piece of the die broke off at the rim (cuds).
Going deeper
These are repeatable within a die's run and are raised on the coin (because they fill voids in the die), which distinguishes them from incuse post-mint scratches. They also mark a die's state and help attribution.
Sources: Professional Coin Grading Service (PCGS) · Coin World
Evidence pages
Varieties: doubled dies, RPMs, and overdates
In plain English
Varieties are built into the die: doubled dies (doubled design from misaligned hubbing), repunched mintmarks (the same mintmark punched twice, offset), and overdates (a new date over an old one). Each appears identically on every coin from that die.
Going deeper
Famous examples include the 1955 doubled-die cent and the 1942/1 Mercury dime overdate. Because the feature is in the die, it is reproduced exactly, the hallmark of a variety, not a one-off error.
Sources: Professional Coin Grading Service (PCGS) · Numismatic Guaranty Company (NGC)
Doubled die vs. machine doubling (don't be fooled)
In plain English
The most common mix-up: a valuable 'doubled die' versus worthless 'machine doubling.' A true doubled die has rounded, notched, separated detail and appears on every coin from that die. Machine doubling looks flat and shelf-like and varies coin to coin.
Going deeper
Machine (strike) doubling is caused by die movement at the moment of striking, so it adds no premium; a doubled die is a die-manufacture feature. Telling them apart protects you from overpaying.
Sources: Numismatic Guaranty Company (NGC) · Coin World
Evidence pages
Key terms in this lesson
Mint Error vs. Variety · Mint Error vs. Post-Mint Damage (PMD) · Off-Center Strike · Broadstrike · Clipped Planchet (Clip) · Cud · Die Crack · Die Clash · Doubled Die · Repunched Mintmark (RPM) · Overdate · Wrong Planchet / Off-Metal Error · Lamination Error · Strike-Through Error · Machine Doubling