Mint-made errors

The punched disks are first known as "type-1" blanks (or planchets). After an upending mill adds uniform rounded rims, the disks are called "type-2" blanks (or planchets). Occasionally, Type-1 and Type-2 blanks aren't further processed, ‘escape’ the mint facility and enter circulation. Type-2 blanks may also be considered striking errors as they are prepared correctly, but are released without having been struck.

Clipped planchet

A misfeed can occur when the metal strip is fed through the blanking machine. The punches sometimes overlap the leading edge of the metal producing a straight clip. Sometimes, the punches strike an area of the strip which overlaps the hole left by the previous strike producing a curved clip.[4] On such curved-clip coins, often the rim opposite the clip shows a distinctive distortion and loss of detail called Blakesley Effect. (See the photo with an example of a clipped planchet nickel: the odd look of the rim near the word LIBERTY is from Blakesley Effect. Sometimes punches strike the irregular trailing edge of the metal strip producing irregular clips.

Coins are sometimes struck on planchets that are either too thin or too thick producing underweight or overweight coins. This can be because the equipment settings cause the metal strip to be rolled to an incorrect thickness or because the metal strip was intended for another coin denomination such as a quarter planchet cut from a metal roll intended for dimes.

Lamination crack on a Jefferson nickel

A lamination flaw is a planchet defect that results from metal impurities or internal stresses. Lamination flaws cause discoloration, uneven surfaces, peeling, and splitting.

A 1963 Lincoln Cent struck before split planchet error. Note the weakly struck obverse (left) and striations on the reverse (right).

A 1963-D Lincoln Cent struck after split planchet error. Note the normal strike on the obverse (left) and lack of design on the reverse (right).

A split planchet coin error occurs when, during the preparation of the planchet strip, impurities such as gas, dirt, or grease become trapped under the surface of the metal blank, creating a weakness or lamination defect. This area of the metal will be weaker and may flake, peel, or split because the adhesion is poor where the foreign material is.[5]

Split planchet errors are normally restricted to planchets composed of a solid alloy, such as U.S. cents and nickels,[6] and the Australian fifty-cent coin.[5] Split planchet errors should not be confused with "separation errors", which only affect clad and plated coins. Separation errors are bonding errors, not alloy errors.[6]

A split can occur either before or after the coin is struck. The descriptive terms split before strike and split after strike are used to distinguish the respective types. A "split before strike" will show design on both sides of the coin, have coarse to fine striations, and will usually be weakly struck. A "split after strike" will show a normal strike on one side, but will have a rough, design-free surface on the other side[7] and will always weigh less than a normal planchet.[8]

Peeled cladding on a Roosevelt dime

Many modern coins are made of layers of different metals known as clads. These cladding layers sometimes peel, fold, or completely separate.

A fundamental die-setting error occurs when the die is not set as the producers intended. For example, in April 2013 the Central Bank of Ireland issued a silver €10 commemorative coin in honor of James Joyce that misquoted a famous line from his masterwork Ulysses[9] despite being warned on at least two occasions by the Department of Finance over difficulties with copyright and design.[10]

Partial date likely caused by filled die

Missing mintmarks, dates, and other design elements are not distinct errors, but rather are what the observer sees when viewing other error types. A design element that is missing from the die when it is made is a fundamental error. Missing design elements that occur because dies are tilted and do not strike the planchet face-on are known as misaligned dies. A design element may be missing because foreign matter such as grease plugs the cavity into which the planchet's metal would normally flow under the striking pressure. This error is also known as a filled die and as a strike through. Although this does involve a die, it is typically thought of as a striking error, but is included here so as to provide a more complete list.

Doubling on LIBERTY from the 1995 doubled die Lincoln cent

A doubled die occurs when a die receives an additional, misaligned impression from the hub. Overdate coins such as the 1942/1 Mercury dime and 1918/7 buffalo nickel are also doubled dies. They are both listed in the CONECA files as class III doubled dies. Class III means the die was hubbed with different "designs" (or hubs that had different dates). They are not repunched dates, since the dates were punched onto the hub.

A die crack is seen to the left of Lincoln's head

Broken die resulting in a "cud" atop Jefferson's head

Dies can crack during use producing jaggeds, raised lines on the surface of subsequently struck coins. In U.S. coinage, many Morgan dollar coins show slight die cracks. Dies with cracks, especially those with cracks near the edge, sometimes break. The broken piece may be retained in position or fall away. Die cracks and retained die breaks can be difficult to distinguish. Retained die breaks cross the coin's face from rim to rim with the area to one side of the break being slightly higher than the other. Coins struck after the break falls away have a raised, rounded, unstruck area along the edge. These coins are known to collectors as cuds. Sometimes, an area of a die will chip out of the center. These so-called die chips appear on subsequently struck coins as raised, rounded, unstruck areas called die chips.

The marks seen above the word LIBERTY were caused by the obverse die clashing with elements on the reverse die intended to impress the space between the memorial columns

A die clash occurs when the obverse and reverse dies are damaged upon striking each other without a planchet between them. Due to the tremendous pressure used, parts of the image of one die may be impressed on the other. Planchets subsequently struck by the clashed dies receive the distorted image. A well-known example is the "Bugs Bunny" Franklin half dollar of 1955, where part of the eagle's wing from the reverse gives Franklin the image of protruding teeth.[11]

1993 MAD clash mark on a U.S. cent

A MAD clash occurs when an obverse and reverse die strike each other while misaligned in relation to each other. Additional misalignment errors are discussed below. MAD is short for "misaligned dies."

Double punched mintmark

Historically, some design elements near the outer perimeter of a die were added by punching because technology made it difficult to press both the central and perimeter design elements at the same time. Also, some dies were made without mintmarks or dates to permit their use at different mints and in later years. A die technician added missing elements by positioning a punch, a small steel rod with the mirror image of a letter or number on it, and striking the punch with a hammer pressing the image into the die. If the image is not strong enough, the technician will punch it a second time. Punches placed in a different position between strikes will produce a doubled image which is called a repunch.[12] Dual punches occur when punching is repeated in a second location. Sometimes technicians use a punch with the wrong or incorrectly sized letter or number. A well known example of a small mint mark is 1945-S "Micro S" Mercury dime, when the mint used an old puncheon intended for Philippines coins.[13] A much rarer example is the 1892-O "Micro O" Barber half dollar, which may have come about from the brief use of a mintmark puncheon intended for the quarter.[14] Exactly the same error occurred with the 1905-O Barber dime, although numerous examples are known of this mistake. Modern equipment virtually eliminates the need to design elements by punching.

In the past, mints used dies until they broke. At the beginning of the year, mints punched a new date over the old on dies that were in use. For 19th-century coins, it is difficult to call an overdate an "error", as it resulted from intentional recycling of the die. An overmintmark occurs when a second mintmark is punched over an earlier mintmark following the transfer of a die from one mint to another. A well-known example is the 1900 Morgan silver dollar, when reverse dies with "CC" below the eagle were sent from the Carson City Mint to the New Orleans Mint, where they were given an "O". A similar case occurred in 1938, when a reverse die for the buffalo nickel was made for the San Francisco Mint, because that year only, the Denver Mint made these coins with a "D" punched over the "S".

Lines, called trails, transfer to coins from dies made using the modern high pressure "single pressing" process. When images are impressed into dies using the process, the displaced metal moves out into fields leaving visible lines on the dies. The dies themselves are called trail dies. Coins on which the lines appear are simply called trails. Trails were first noted on Lincoln Memorial steps found on the reverse of one cent coins minted from 1959 to 2008. The trails gave the steps the appearance of being wavy. The term wavy steps is still used to refer to trails found on the memorial steps, but the term trails is more commonly used to refer to lines found elsewhere.

Great Britain dateless double obverse "mule" halfpenny Edward VII 1902 to 1910, well circulated obverse. What looks like a mint error is actually a cleverly made up double headed coin, just slightly under weight.

The reverse of that same coin was also minted with an obverse die, but on a different flan. The two obverse parts were cleverly put together from two different coins. This manipulated coin was found in Australia where it was legal tender. It could have been used in the very popular Australian Two-up game in a fraudulent way.

A coin struck using dies never intended for use together is called a "mule". An example is a coin struck with dies designed for different coin denominations, or a coin struck with two dies that both lack a minting year on them, resulting in a 'dateless' coin.

Because of misalignment, the obverse of this coin is off-center but the reverse is centered

Dies must be properly aligned in presses for coins to be struck correctly. Errors occur when dies are offset, tilted, or rotated. Offset errors occur when the hammer die is not centered over the anvil die typically resulting in an off-centered obverse, but centered reverse. Tilting errors occur when die surfaces are not parallel producing coins that are thinner along one edge, and sometimes causing missing design elements along the opposite edge because of insufficient pressure being exerted on that edge. Rotation errors occur when the images on the obverse and reverse dies are turned from the normal positions such as when the reverse image is at a right angle to the obverse.

Broadstrike errors are produced when the collar die (the circular die surrounding the lower die) malfunctions. The collar prevents the metal of the blank from flowing outside the confines of the die. All denominations of U.S. coins with a broadstrike have plain edges.

A "strike-through" coin is made when another object comes between a blank and a die at the time of striking. That object's outline is pressed into the blank's surface. Common examples include hard objects such as staples, metal shavings, and other coins as well as soft objects such as cloth and grease. Hard objects leave sharp outlines and, on occasion, adhere to the blank producing a coin called a "retained strike-through". A planchet "struck-through" a coin is left with an impression of the coin called brockage (discussed below). When the "strike-through object is a blank planchet the result is a uni-face coin with one struck side and one blank side (see below). When the "struck-through" object is another coin, and that coin adheres to a die(as opposed to the other coin), the adhered coin is called a "die cap" (discussed below). Two coins which adhere to one another are called "bonded pairs". Softer objects, such as grease, can fill crevices in a die, producing a weak strike with a smudged appearance. These errors are often called "missing element coins" (discussed above and as "filled dies"). (A great example of such an error occurred in 1922, when only the Denver mint struck Lincoln cents. As a result of the mint attempting to speed up production, such a large amount of excessive grease was applied to the dies that the mintmark was obscured and therefore either nonexistent or weakened on the 1922 cents. These are very popular with collectors.)[15]

Uni-face coin (blank reverse)

A uni-face coin results when two planchets are stacked one atop the other at the time of striking. This produces two coins: one with only an obverse image, and a second with only the reverse image. The planchets may be centered over the die producing one complete image on each coin or off-centered producing partial images on each side. In the accompanying image of the blank reverse, the shadow or outline of Lincoln's profile from the obverse side of the coin is visible.

Die cap

A struck coin remains on a die and leaves its slowly fading impression (called brockage) on subsequently struck coins[16] and, over time, changing shape to resemble a bottle cap.

The brockage image of the Lincoln memorial can be seen near the bottom of the coin

Brockage occurs when a mirror image of a coin is struck on a blank. After a struck coin fails to eject, a new blank is fed between the struck coin and the hammer die. The hammer die strikes the second blank leaving its image on one side while pressing the blank against the previously stuck coin which sinks its image into opposite side. Most brockages are off-center, but fully overlapping brockages are the most desirable.

There are two types of edge strikes. A standing edge strike occurs when a blank "bounces" so that it is standing on edge as it is struck. Striking pressure produces edge indentations where the dies strike, and sometimes bends the blank. Repeated strikes can produce a coin that is folded flat. . Chain edge strikes occur when two blanks are fed into the space between dies at the same time. The blanks expand when struck and press together leaving each with single indented edge. Two chain edge struck coins together are known as a matched pair.

Lincoln cent with second off-center strike

Flip-over multi-struck coin

A multiple strike, also referred to as a double exposure, occurs when the coin has additional images from being struck again, off center. The result is sometimes mistaken for being a "doubled die". On occasion, a coin will flip over between strikes so that the second image is that of the opposite side of the coin.

Lincoln cent struck off-center

An off-center coin is produced when the coin is struck once, albeit off center. Unlike a broadstrike, the punch is not in the center of the coin, but rather the edge. This results in a coin which is not circular. The coin gives a freakish appearance as a result, and various amounts of blank planchet space are visible. The coins can vary in value because of how far off center they are struck, although coins with full dates are more desirable than coins without a date or missing digits.[17]

A double denomination coin is one that has been struck twice between different denomination dies such as once between nickel dies and again between quarter dies. The term is sometimes used to refer to a coin struck on the wrong planchet (see below).

Nickel struck on one cent planchet

Sometimes planchets for one coin denomination are fed into a coin-stamping press equipped with dies of another denomination. This results in a coin that has been stamped with a design intended for a differently sized coin. The resulting errors are prized by collectors, though they are usually caught during the manufacturing process and destroyed. Such errors are sometimes called "double denomination" coins, but that term is also used to refer to coins struck a second time with dies of a different denomination.

Some examples include cents struck on dime planchets, nickels on cent planchets, or quarters on dime planchets. This type of error should not be confused with the much rarer mule which is a coin struck between dies that were never intended to be used together such as a coin with nickel obverse and a dime reverse.

Wrong-planchet errors may also occur when the composition of the coin changes. Such situations generally arise when the mint has decided to change the alloy or plating of the coin in the new coinage year, but a few planchets from the previous year—and thus of the previous composition—have yet to be struck. Should the dies be changed for the new year while the old planchets are awaiting striking and not removed, coins using the old composition will be struck with the new year's date. Such coins are rare and often highly valued by collectors, as with the 1943 copper cents and 1944 steel cents.

A much rarer error is a denomination struck on a foreign planchet. This did occur occasionally with United States (and before that American colonial) coinage in the 17th, 18th, and 19th centuries. In the 20th century, fewer errors on foreign planchets are discovered but they still occur when the US Mint is contracted by foreign governments to produce coinage for them. Recent encapsulations and sales at auctions reveal 1995 and 1996 examples of mintages on foreign planchet. A few 1996 Lincoln cents were struck on stock designated for Singapore. There are 1997-D, 1998 and 2000 dated Lincoln cents struck on foreign planchets, but not identified by PCGS or NGC as to the country the mintage was intended.

Blanks are surrounded by collars when struck to prevent the blank from flattening and spreading. Edge and rim errors occur when collars are either out of position or are deteriorated. A wire rim occurs when excessive pressure squeezes out metal between the collar and the edge of the die producing an extremely high thin rim. A partial collar occurs when an out-of-position collar leaves a line around the coin which is visible when looking at its edge. A partial collar is sometimes called a railroad rim when a reeded edge coin is involved as the line resembles a rail and the reeds resemble railroad ties.

A collection of two or more coins struck at the same time or during successive strikes on one or more dies, these coins with the resulting errors are related to one another, fitting together as a set.[18] All brockages, indents, chain edge strikes, and capped die strikes have a corresponding coin, but are rarely found together. A single coin of the set may be discovered by mint staff during quality control and removed, or the coins may be separated into different lots to be distributed separately into circulation.