A coin is worth more as an error only when the mistake happened at the Mint while the coin was being struck. Doubled dies, off-center strikes, clipped planchets, wrong-planchet strikes, die cracks and cuds all count. Most coins brought to us as errors are damage, wear, plating trouble or machine doubling, and those sell for face value or for their metal.
Struck that way or changed later
A genuine error left the Mint already wrong. The die, the blank or the press slipped during striking, and the coin came out of the press with the flaw. Damage is anything that happened after that, in a pocket, a parking lot, a coffee can, a garden bed or a garage workshop.
One home test is to ask where the metal went. During a strike, metal flows up into the die, so real errors tend to show raised features with smooth, rounded edges and the same luster as the rest of the coin. Post-mint damage usually pushes metal down or scrapes it away. Dents and gouges sink into the surface, and the metal beside them often gets shoved up into a little ridge.
Color and surface give clues too. A mark that is brighter, duller or a different shade from the metal around it usually came later. So does anything with tool marks, file lines or a shine that looks rubbed in.
Coins squeezed in a vise, hammered thin or flattened on a railroad track can look strange enough to pass for errors. The design on those coins is stretched or squashed but still all there, and the rim is crushed instead of missing. Lettering that leans or smears in one direction is another sign of pressure applied after striking.
Doubled dies versus machine doubling
Doubling is the error we get asked about most, and the one most often misread. A true doubled die starts with the die itself. When the die was made, the design was pressed into it more than once and slightly out of line, so every coin struck from that die shows the same doubled letters or numbers.
On a doubled die, the extra image is raised and rounded, often close to the full height of the first one. Look for small notches at the corners of letters where the two outlines meet. The doubling repeats in the same pattern on every coin from that die, which is how collectors catalog them.
Machine doubling, also called strike doubling, happens when the die bounces or shifts a hair during the strike. It leaves a flat step beside letters and numbers, like a shelf, as if the design had been smeared sideways. The second image is low with squared edges. Machine doubling is common, and collectors pay little or nothing extra for it.
A worn die causes a third look-alike. Late in a die's life the edges of the design go soft and puffy, and coins struck then show a blurry halo around the lettering. That is die wear, and nobody catalogs it as a doubled die.
| What you see | Likely cause | Collector interest |
|---|---|---|
| Rounded second image with notches at letter corners | Doubled die | Can be strong, depending on the coin and how clear the doubling is |
| Flat, shelf-like step beside letters | Machine doubling | Little or none |
| Soft, blurry halo around the design | Worn die | Little or none |
| Doubled letters with tool marks cut around them | Altered after it left the Mint | None |
Plating bubbles, corrosion and other look-alikes
Cents made since 1982 are copper-plated zinc. When moisture gets under that thin copper skin, the zinc swells and corrodes, and the cent grows blisters, bubbles or bald patches of gray metal. These are some of the most common pieces people bring us as errors. They are environmental damage, and a bubbled cent is worth one cent.
Environmental damage covers anything the world did to a coin after it left the Mint. Coins dug out of yards, left in damp basements, wrapped in rubber bands or stored against old paper can pick up green crust, black spots, pitting or odd rainbow colors. Coins that sat through a house fire can come out discolored or rough.
Color fools a lot of people. A silver-colored cent from any year other than 1943 almost always got its color later, from plating or chemicals. The 1943 cents really are zinc-coated steel, which is why they look gray. A gold-colored nickel or dime usually means someone plated it at home or a novelty shop did.
A soft or missing letter often comes from grease or debris that filled part of the die. Collectors list these struck-through and filled-die coins as minor errors, and most add little to a coin's price.
Error types collectors look for
Collectors pay for errors they can see plainly. A buyer looking at a true off-center strike or a wrong-planchet coin does not need to squint or argue about it.
Size and placement count for every type. A bold error on the face of the coin draws more interest than a faint one near the edge, and errors on older or silver coins have their own following. These are the types worth setting aside for a closer look.
A coin can carry more than one of these at once, such as a clipped planchet that was also struck off center. Those pieces get noted line by line, since each flaw adds to the story.
- Off-center strike: the design sits shifted to one side and part of the blank is smooth. Collectors care how far off center it is and whether the date still shows.
- Clipped planchet: a curved or straight bite is missing from the edge because the blank was cut short. On a real clip the raised rim fades out near the missing piece. A clip made with snips leaves a sharp cut with the rim running right to it.
- Wrong-planchet strike: the coin was struck on a blank meant for another denomination or metal. Color, size and weight all look off, and part of the design may run past the edge.
- Die crack: a thin raised line that wanders across the design, left where metal filled a crack in the die. A scratch cuts into the coin and sits below the surface.
- Cud: a raised, shapeless blob of metal joined to the rim, where a piece of the die broke away.
- Doubled die: rounded, full-height doubling that repeats on every coin from the same die.
Storing and showing a suspected error
How you handle a possible error before a sale protects what it can bring. Never clean it, polish it, scrub off corrosion or dip it in anything. A cleaned coin grades lower, and on an error it can also blur the detail a buyer needs to see.
Hold coins by the edges, over a towel or a soft surface. Put each suspected error in its own small paper envelope and write on the outside what you think it is and where it came from, such as a bank roll, a jar or change from a store. Keep those envelopes apart from the rest of the coins so nothing rubs.
A few notes help us move faster at the appointment: the year and mint mark, what caught your eye, and whether more coins came from the same roll or bag. A phone photo under good light is handy, though we evaluate the coin itself.
At the appointment we look at each piece under a magnifier in front of you, check the metal with non-destructive testing and weigh it on a calibrated scale. Weight helps separate a wrong-planchet coin from one that was plated. Your written, item-by-item list says which pieces are mint errors, which are damage, and which deserve a look from a grading service.
When grading an error is worth the cost
PCGS and NGC both grade error coins. Each one goes into a sealed plastic slab with the error type printed on the label. A slab tells a future buyer that the error is real and what grade the coin is. For a clear, sought-after error in good condition, that can widen the pool of buyers and make the coin easier to sell.
Grading costs money and the coin is gone for weeks or longer. It rarely makes sense for machine doubling, small die cracks, minor clips on modern cents or anything with post-mint damage, since collectors will not add enough to cover the fee.
Our written list flags the pieces where grading could pay off and the ones where it would not. You can keep a coin and send it to a grader yourself, sell it to us raw, or sell it to us after it comes back in a slab. We buy graded and ungraded error coins.
Error coins from Denver change and Denver jars
The Denver Mint on West Colfax Avenue began striking coins in 1906, and its coins carry a D mint mark. Plenty of the errors that turn up around the metro came out of that building, so a D is a good thing to note on any suspect. Denver cents carry the D under the date, which is also where people tend to spot doubling first.
Most of the error hunting we hear about starts with bank rolls, a jar that sat in a closet in Englewood or Arvada for decades, or a father's coin album from a Park Hill or Wash Park house. Older jars often mix copper-plated zinc cents with bubbled plating in among wheat cents, and sorting the two is the first job. Coins dug from yards and gardens in older parts of the city, from the Highlands to Platt Park, usually carry pitting and green or black spots from the soil. That is ground damage, even when the coin looks odd enough to be an error. Cents pulled from bank rolls deserve a look under a lamp before they go back into circulation.
We look at suspected error coins by private appointment anywhere in the Denver metro and Boulder. There is no counter and no audience, so you can lay out a whole roll of suspects and ask about each one without feeling rushed. Bring the coins as they are, uncleaned and in their envelopes, and have a government-issued photo ID with you if selling is on the table. Call 303-401-0104 for a callback the same business day. For a box of rolls or a large accumulation from an estate, ask about a home visit.