What an error coin is, and what it is not
A mint error is a coin that left the mint with a defect introduced during manufacture. The defect happened before the coin entered circulation, at one of three points: when the die was made or while it was in use, when the blank metal disc was prepared, or when the die struck the planchet. Everything else — every scratch, dent, gouge, bend, chemical stain, and vise job that happened after the coin left the press — is post-mint damage, and it is not an error.
That distinction is the entire discipline. Damage is unlimited in variety because anything can happen to a coin in a pocket, a drawer, or a garage. Errors are limited because the mint's processes are limited. A genuine error always corresponds to a specific mechanical cause, and learning those causes is how you learn to identify the coins. If you cannot name the process that produced the feature you are looking at, you have not identified an error yet.
This site is built around four families. Three of them are errors. The fourth is the category that catches the majority of coins people bring to a dealer or post online: things that look like errors and are not. Read that fourth family as carefully as the first three. The not-an-error hub exists because it is where most of the traffic on this subject actually belongs.
The three error families
Die errors originate in the die. The design on the die is wrong or the die is damaged, so every coin it strikes carries the defect until the die is replaced. Doubled dies, repunched mint marks, die cracks, cuds, die chips, and die clashes belong here. Die errors are the most collected family because they repeat: a doubled die produces thousands of identical coins, which makes them cataloged, attributable, and comparable. Doubled dies have their own hub.
Planchet errors originate in the blank. The disc of metal that goes into the press is the wrong size, the wrong alloy, incomplete, or internally flawed. Clipped planchets, laminations, split planchets, wrong-metal and wrong-denomination planchets, and unplated cents belong here. Planchet errors are unique to each coin, not repeated, so they are attributed by type rather than by catalog number.
Striking errors originate in the press. The planchet is in the wrong position, the collar is missing, the dies are misaligned, something is between the die and the planchet, or the coin is struck more than once. Off-center strikes, broadstrikes, brockages, capped dies, struck-throughs, double strikes, and die-adjustment strikes belong here. Like planchet errors, each is unique. Mint error types explained is the hub for the planchet and striking families together, organized by the mechanical cause of each.
Every suspect coin belongs to exactly one family. Sort first, identify second, value last.
The triage method
Start every examination the same way, regardless of what you think the coin might be. The order matters, because the early steps eliminate the common explanations before you spend time on the rare ones.
- Write down what you see before you decide what it is. Describe the feature in plain words: raised or incuse, sharp or mushy, on one side or both, near the rim or in the field. Observations before attribution explains why this step prevents most misidentifications.
- Ask whether the feature is raised or incuse. Anything struck by a die is raised on the coin, because the die is incuse. A feature that is cut into the coin — a scratch, a gouge, a punch mark — was made after striking, with a tool. This single test eliminates most damage.
- Look at the edge. Off-center strikes, broadstrikes, clips, and wrong-planchet errors all show on the edge. Damage rarely does. Photograph the full edge before you go further.
- Weigh the coin. Wrong-metal and wrong-planchet errors are confirmed by weight, and so is the 1943 copper cent. Nothing else settles those questions. Calibrate your scale first; an uncalibrated scale is worse than none.
- Check for doubling of the right kind. If the feature is doubled lettering or a doubled device, decide whether it is die doubling, machine doubling, or die deterioration. The tests are specific and covered in machine doubling versus doubled die and die deterioration vs true doubling.
- Name the process. If you can state which mint process produced the feature, you have a candidate error. If you cannot, you have damage or a die state, and the not-an-error hub will tell you which.
- Only then look up value. Search completed sold listings for certified examples of the same error type on the same denomination. Asking prices are not evidence; sold prices are.
Die errors in brief
A doubled die is a die on which the design was impressed more than once, misaligned, during the die's manufacture. Every coin struck from it shows the same doubling in the same place. Doubled dies are attributed by catalog number, and the famous ones are famous because they are dramatic; most are minor and worth little. The identifying features are separation between the two images, rounded secondary images at the same height as the primary, and notching at the corners of letters where the two images overlap.
A repunched mint mark occurs on coins from the era when mint marks were punched into each die by hand. If the punch was applied more than once in slightly different positions, the coin shows a mint mark with a second, partial image beside or beneath it. Repunched and over-mint-marks are cataloged like doubled dies and are common on some dates.
Die cracks, die chips, and cuds are progressive damage to a die in use. A crack shows as a thin raised line on the coin; a chip is a small raised blob where a piece of the die surface broke away; a cud is a raised, featureless area at the rim where a piece of the die broke off entirely. They are related and often confused, and the comparison sorts them out. Their value depends almost entirely on size and drama; tiny die chips are the most overpriced items in the error market.
A die clash occurs when the dies strike each other with no planchet between them, transferring a faint incuse image of one die to the other. Coins struck afterward show a ghost of the opposite side's design in the fields. Clashes are common, usually minor, and occasionally spectacular.
Planchet errors in brief
A clipped planchet is a blank punched from the strip where the punch overlapped a previous hole, the strip edge, or a defect. The coin is missing a piece with a characteristic shape: curved for an overlapped hole, straight for the strip edge, ragged for an unfinished strip end. Genuine clips are confirmed by the Blakesley effect, a weakness in the rim directly opposite the clip caused by uneven pressure in the upsetting mill. Photographing the Blakesley effect is the confirmation test.
A lamination is a flaw in the metal where a layer separates and peels, before or after striking. It appears as a thin flap or a shallow, irregular missing area with a distinctive layered edge. Laminations are common on some alloys and dates and are frequently confused with environmental damage; the damage comparison covers the tell.
A wrong planchet error is a coin struck on a blank intended for another denomination or another country, or on the wrong alloy. These are confirmed by weight and diameter, never by color; color does not prove wrong metal because plating, toning, and chemical exposure all change color. Genuine wrong-planchet errors are rare and valuable, which is why fakes are common.
A split planchet separates into two thin halves along an internal flaw, either before striking, producing a thin coin with a rough face, or after, producing two halves that were once one coin.
Striking errors in brief
An off-center strike occurs when the planchet is not fully within the collar when the dies come down. Part of the design is missing and the coin has a blank, crescent-shaped area. Off-centers are valued by percentage and by whether the date is visible; estimating the percentage is a skill in itself. A broadstrike is struck without the collar at all: the full design is present but the coin spread wider and thinner than normal. A misaligned die strike has one die off-center while the other is normal. The three compared is the reference for telling them apart.
A brockage is a coin struck against another coin that stuck to the die, producing a mirror-image incuse impression of that coin's design on one side. A capped die is what happens when a coin stays stuck to the die through many strikes, deforming into a cap. A struck-through is a coin struck with a foreign object between die and planchet — grease, cloth, wire, a fragment — leaving a weak, missing, or textured area. A double strike is a coin struck twice, with the second strike offset, rotated, or flipped.
The fourth family: not an error
Post-mint damage is anything done to a coin after it left the mint. Scratches, gouges, dents, bends, holes, vise and roller marks, acid and chemical damage, heat damage, and deliberate alterations. Damage is incuse or displaces metal in ways a die cannot; it has sharp, bright edges on an otherwise worn coin; and it has no mechanical explanation from the minting process. It is by far the most common thing brought to an error dealer.
Machine doubling is a flat, shelf-like doubling caused by die movement during or after the strike. It is common, it is not a doubled die, and it has essentially no value. It is the most common misidentification in the hobby. Die deterioration doubling is a mushy, swollen doubling near the rim from a worn die; it is also common and also not a doubled die. A missing mint mark on most series is not an error because Philadelphia coins did not carry one for most of US history.
Every one of these has its own page, and the not-an-error hub organizes them. If you take one thing from this guide, take this: check the fourth family first.
Attribution, certification, and value
Attribution is the assignment of a specific catalog identity to a die error — this doubled die, this repunched mint mark — by comparison to a reference listing. The references are CONECA's files, the Wexler listings, the Cherrypickers' Guide, and for Morgan dollars the VAM system. Attribution is a specialist skill, and the major grading services offer it as an add-on service. Planchet and striking errors are not attributed by number; they are described by type and certified as genuine.
Certification puts the error in a holder with the grading service's opinion that it is genuine, its type, and its grade. For any error of meaningful value, certification is close to mandatory, because the market for raw errors is small and skeptical. Error coin grading and certification covers the services, the fees, and what to submit.
Value is set by three things: the dramatic visibility of the error, its rarity for that denomination and date, and its grade. A large off-center on a modern cent is common and cheap; the same percentage on a silver dollar is scarce and expensive. A famous doubled die in high grade is a trophy; a minor one is a curiosity. In every case the reference is sold prices for certified examples, found by searching the error type and denomination and filtering to sold. This site never quotes values because they change and because the honest answer to what a coin is worth is always the same: look at what people paid last week.
Equipment and habits
You need magnification, light, and a scale. A loupe at moderate power and a raking light source — a light held low and to the side — reveal doubling, die cracks, and surface texture that overhead light hides. A USB microscope with the right settings lets you photograph what you see. A digital scale reading to hundredths of a gram, calibrated, settles planchet questions. A reference for standard weights and diameters by denomination and date completes the kit.
The habits matter more than the equipment. Describe before you attribute. Check the fourth family before the first three. Look at the edge. Weigh anything that might be a wrong planchet. Compare to certified examples before you believe your own eyes. And never clean a coin: cleaning destroys surfaces, destroys value, and turns a possible error into a certain Details grade.
Where this guide leads
- For doubled dies, repunched mint marks, and the doubling tests: Doubled die identification.
- For every planchet and striking error by mechanical cause: Mint error types explained.
- For everything that is not an error, and why: The not-an-error hub.
- For getting a confirmed error certified: Error coin grading and certification.
- For the specific confusions, the comparison series: machine doubling vs doubled die, error vs damage, off-center vs broadstrike vs MAD, cud vs crack vs chip, the 1943 copper cent.
For grading services in general, the sister site GradedCoins.co covers slabs, labels, and submission. For the coins themselves, VintageCoins.co covers pre-1965 US coinage.
The fastest education in error coins is looking at certified ones. Search by error type and study what the graders confirmed.
Frequently asked questions
How do I know if my coin is an error or just damaged?
Ask whether the feature is raised (struck by a die) or incuse (cut in afterward), look at the edge, and ask which mint process could have produced it. If no process explains it, it is damage. The not-an-error hub covers the common cases.
Are error coins valuable?
Some are. Value depends on how dramatic and visible the error is, how rare it is for that denomination and date, and the grade. Most minor errors are worth little. Check sold prices for certified examples of the same type.
Should I get an error coin certified?
For anything of meaningful value, yes. The raw error market is small and skeptical, and certification is what makes the coin sellable. For minor errors the fee may exceed the value.
What is the most commonly misidentified error?
Machine doubling mistaken for a doubled die. It is flat and shelf-like, it is common, and it is not an error.
Can I clean an error coin to see it better?
No. Cleaning destroys the surfaces and the value, and it guarantees a Details grade at certification. Use light and magnification instead.