Part VII. Post-Strike Mint Modifications:

Embedded Matter:

Lettering Die Inclusion

Definition: Foreign matter that is forced into the edge of a manganese-brass clad dollar coin by the lettering die.  Such errors may be difficult to distinguish from foreign matter forced into the edge of a planchet during the upsetting process.  The main difference is that a lettering die inclusion will protrude from the coin’s edge while an upset mill inclusion will be flush with the edge.

This 2007-P Jefferson dollar has a spiral metal shaving embedded in its edge.  Strongly attracted to a magnet, it’s probably composed of steel.  The right arm of the U of PLURIBUS is deeply impressed into the metal shaving because of the latter’s tight fit against the lettering die.  Discovered by Troy Shoopman.

Part IV. Die Errors:

Die Damage:

Accidental Die Abrasion

Definition: Abrasion to the die face that occurs by accident.  The abrasion can occur in a single incident or may be the result of continual scraping of the die face against a machine part (like a feeder).  As with intentional die abrasion, the chief result is a localized lowering of the die face which may remove shallowly recessed design elements.  Accidental die abrasion is often accompanied by die scratches or die scrapes.  These are generally straight, relatively wide, and rather uniform in appearance.  Die scratches caused by intentional die abrasion are much finer and often point in many different directions, although there are exceptions, especially among recent issues like Sacagawea dollars.

This 1998-P quarter dollar shows accidental die abrasion affecting the area around Washington’s eye and nose.  Areas of shallow relief, like the medial corner of the eye, have been lost.  Coarse, straight, parallel die scrapes run through the affected area.  The damage was most likely inflicted by a mis-timed feeder.

The reverse face of this 1944 cent shows an area of accidental die abrasion that approximates the shape of a right triangle.  Enough metal was removed from the die face to create a distinct rise on the coin’s surface which almost swallows up the letters LURI of PLURIBUS.  Die damage of this type — both unilateral and bilateral — occurs in the same area in Lincoln cents that date from 1917 to 1945.  The repetitive nature and consistent appearance of the damage strongly indicates a machine part is responsible.  While a feeder is a likely candidate, the theory has yet to be proven.  Damage in this area can take the form of abrasion, a die dent, or a combination of both types of errors.

Part IV. Die Errors:

Die Deterioration/Deformation Errors:

Die Subsidence Errors:

Recurring Die Subsidence Errors:

Definition: Die subsidence (sunken die) errors are usually one-off events.  In other words, the error will only affect one die.  When die subsidence errors affect several dies, it’s usually the periphery of the die face.  This makes sense as differences in hardness would be expected to develop during flawed heat treatment (annealing, tempering, quenching).  These processes cool or heat up a die from the outside in, and circular or semicircular zones of weakness can develop in the case of heat-treatment that is too rapid, too slow, or that is interrupted in some fashion.

The real mystery arises when you end up with highly localized, repetitive die subsidence errors in the same location well within the die face.

The most widespread epidemic of repeated interior die subsidence errors occurs among 1973-D cent.  Only the reverse die is affected and at least 8 dies are represented.  The defect is always found on the left side of the Lincoln Memorial, between columns 1 – 3.  The outline and height of the zone of subsidence is slightly different from die to die, but the location is quite consistent.  Why only the reverse die is affected, and why the abnormally soft patch of steel is restricted to this area, is a profound mystery.  These defects are often mistaken for clash marks.

Another group of repetitive die subsidence errors is found among 1988-P nickels.  At least two obverse dies are affected.  The top of Jefferson’s head develops a smooth swelling.

These three 1973-D reverse dies display a repetitive die subsidence error on the left side of the Memorial.  The columns, roof, and base of the Memorial are often visibly distorted as they cross the zone of subsidence.

This 1988-P nickel displays a smooth swelling at the top of Jefferson’s head.  At least one other die suffers from the same defect, which is where the die steel sank in.

Part III. Die Installation Errors:

Use of Canceled and Defaced Dies

Definition: When a die is pulled from service it is first defaced before being sent out to be recycled.  When a design is retired, the remaining dies are canceled or defaced so that no further coins can be struck.  Installation of a canceled or defaced die is unlikely to be an accident and the coins struck by them must be considered intentional errors.

A coin struck by canceled dies will still show most of the design, but the surface will be crossed by one or more thick ridges that may run in parallel or may intersect.  These ridges represent grooves cut into the die face.

A coin struck by defaced dies will show little of the design. Surface details are replaced by a coarsely textured or lumpy surface.

No examples exist of coins struck by canceled or defaced dies within the U.S. Mint.  Several examples are known from other countries. These include a bimetallic 1994 Hong Kong 10 dollar coin with two parallel ridges on each face.  We also have the unique Egyptian coin described below.

This Egyptian 25 piastres planchet was first struck 80% off-center by 25 piastres dies.  It was then struck within a 50 piastres collar by a pair of 2010 Egypt 50 piastres dies that had most of the design ground off.  The defaced 50 piastres dies only contacted the unstruck portion of the off-center 25 piastres coin.  The struck tongue was left untouched by the second strike because its reduced thickness was apparently less than the minimum die clearance of the 50 piastres press.

The 50 piastres reverse die was rotated approximately 120 degrees counterclockwise relative to the obverse die (medal rotation is normal).

The 25 piastres denomination is struck on a planchet composed of nickel-plated steel while the 50 piastres design is normally struck on a planchet composed of brass-plated steel.  We therefore have in this double-denomination error the rare trifecta of a planchet error (off-metal/wrong planchet), a die error (defaced), and a striking error (off-center first strike and rotated die error on second strike).

Part IV. Striking Errors:

Foreign Object Chain Strike

Definition:  A conventional chain strike occurs when the expanding edges of two adjacent discs of coin metal (2 planchets, 2 coins, or one of each) meet and flow together.  A foreign object chain strike occurs when the edge of a coin metal disc and the edge of a foreign object meet and flow together.  Right now, the only recognized foreign object chain strikes involve one member of a pair of feeder/ejection fingers that extend from the same feeder arm.  These errors can therefore also be classified as a form of machine part impingement. Foreign object chain strikes involving other intrusive elements would be hard to recognize, unless they left a tell-tale residue on the edge of the coin or if they left the chain-struck edge with a very peculiar shape and/or texture.

The vast majority of foreign object chain strikes co-occur with a form of intra-strike damage at the opposite pole produced when the protruding portion of the off-center coin is pushed into the other feeder/ejection finger.

Most foreign object chain strikes are seen in multi-struck coins.  These are invariably struck by inverted dies installed in the high-speed Schuler press.

This off-center dime shows a foreign object chain strike on the right side.  Here the edge of the dime and the internal edge of a feeder/ejection finger met and flowed together.  The edge of the dime is slightly convex and bears a 13 millimeter long contact facet.  The opposite pole was pushed in when the protruding portion of the off-center coin was pushed into the other feeder/ejection finger. This form of intra-strike damage almost always accompanies a foreign object chain strike.  The two together form a pattern of bilateral machine part impingement.

This quadruple-struck nickel shows a foreign object chain strike on the right side.  Here the expanding edge of the nickel met the expanding edge of a feeder/ejection finger, leaving the former with a relatively straight edge.  At the opposite pole we again see impact damage from the other feeder/ejection finger.

Part VI. Striking Errors:

Machine Part Impingement

Definition: This error occurs when a coin is pinned and pinched between two machine parts during the strike.  For modern US coins struck with inverted dies in a high-speed Schuler press, the two machine parts are paired feeder/ejector fingers that form the arms of a notch that cradle the planchet and (subsequently) the newly-struck coin.  The feeder/ejection fingers lie at the expanded tip of feeder/ejector arm that looks like a wrench.  Each “wrench” is one of many that fit into a rotating plate that fits the definition of a rotary or dial feeder.

Machine part impingement errors are associated with off-center strikes and with double- and multi-struck coins in which most of the strikes are off-center.  When the dies strike the off-center planchet or coin and the off-center feeder that cradles it, the two elements expand radially.  The facing edges flow together, leaving the coin with a convex facet we call a “foreign object chain strike”.  The portion of the planchet or coin that projects outside the striking chamber is pushed laterally by the expanding coin metal and expanding feeder metal.  The pole opposite the convex facet collides with the other arm of the feeder/ejector, leaving the edge of the coin with a dent and often a warped surface.

This off-center dime was pinned and pinched between two machine parts.  The right side of the coin shows a gently convex foreign object chain strike.  Here the expanding edge of the dime collided with the expanding internal edge of the feeder/ejection finger.   At the opposite pole, the unstruck portion of the dime was pushed laterally into the other feeder/ejection finger.  This collision pushed in the planchet’s edge, warping the unstruck portion of the dime.  This is an example of intra-strike damage.

This quadruple-struck nickel was pinned and pinched between two feeder/ejection fingers during the last three strikes.  After a normal first strike, the nickel received three closely-spaced off-center strikes that are well-separated from the initial strike.  This is a typical pattern for multi-strikes suffering from machine part impingement.  It’s almost certain that the misplaced and mistimed feeder/ejection arm prevents the coin from leaving the striking chamber entirely.

On the right side there is a long, relatively straight contact facet that represents a foreign object chain strike.  Once again, the culprit is one of the two feeder/ejection fingers that cradle the coin.  The left side of the coin was pushed in when the portion of the coin lying outside the striking chamber was pushed into the other feeder/ejection finger.

Part IV. Die Errors:

Clashed Dies:

Raised Clash Marks

Definition:  Clash marks are generated when dies collide in the absence of a planchet.  Each die transfers part of its design to the opposite die in the form of faint, raised, normally-oriented design elements.  Clash marks are generally confined to the field portion and shallowest devices of the die face.

While clash marks are expected to appear on a coin as incuse, mirror-image features, there are exceptions, both real and apparent.

Raised clash marks may occur in the event of a relatively light collision.  If, on the die face, a narrow strip of field is situated between two relatively broad elements, only that narrow strip will make an (incuse) impression on the opposite die.  The coin will therefore show a correspondingly raised, mirror-image design element.

Two “flames” erupt from the roof of Monticello on this 1983-P nickel.  They represent a pair of identical, offset, raised clash marks that depict the gap between Jefferson’s neck and queue (“ponytail”).

The reverse face of this 2001-P Vermont quarter dollar shows a raised clash mark that has been whimsically interpreted as a vapor cloud emerging from the maple-tapper’s mouth.  The “winter breath” clash mark is actually the area where Washington’s wig meets his neck.

Raised clash marks are also the inevitable result of a clash involving design elements intended to be incuse on a coin.  The corresponding features on the die face are therefore raised, and they will penetrate the opposing die in the event of a clash.  The resulting incuse, normally-oriented accessory design elements will be transferred to a coin as raised, mirror-image design elements.

The reverse design of the New Hampshire quarter contains the incuse legend OLD MAN OF THE MOUNTAIN.  When transferred to the obverse die, they appear on the coin as raised, mirror-image letters.  On this particular 2000-P New Hampshire quarter, behind Washington’s inverted head. we find the letters (OL)D MA(N) on the top line and (O)F TH(E) on the next line.

Part II. Die Varieties:

Deeply-Punched Mintmark

Face-on and oblique views of a high-standing mintmark in a 1987-D cent.

Part X. Wastebasket/Composite Categories

Embedded Matter:

Squeezed-In Debris

Definition:  There are numerous entry points inherent in the minting process that allow foreign material to embed itself into a blank, planchet or coin.  A relatively uncommon entry point occurs in the upset mill.  The grooves in the upset mill can trap material that is then transferred to the edge of a blank as it is transformed into a planchet.  There are two major forms of “squeezed-in” debris, discrete pellets and broad, thin sheets of metal.  In the case of the former, small bits of metal or other foreign matter are forced into the edge of the planchet. In the case of the latter, thin sheets of metal — often with a composition strikingly different from the coin itself — wrap around the edge of the planchet, and are eventually struck into one or both faces as well as the coin’s edge.

Embedded in the edge of this 1968-D cent is a small pellet of non-magnetic, nickel-colored metal.

Embedded in the edge of this 1998-P half dollar is a small piece of ferromagnetic metal (probably steel).

Part VI. Striking Errors:

Struck-Through Errors:

Filled Collar / Obstructed Collar

Definition: It’s very seldom that a collar will accumulate dirt or debris, as it’s largely self-scouring.  Each time a newly-struck coin is ejected, it tends to carry with it anything that might have settled against the working face of the collar.  Nevertheless, once in a great while material will remain behind, lodged against the collar.

 As you might expect, reeded issues are the only ones in which this error type is known.  The grooves in the working face of the collar are more likely to accumulate foreign matter than are the smooth collars used for cents and nickels.

If the foreign matter rises no higher than the ridges on the working face of the collar, the edge of the affected coin will lack reeding for several arc degrees.  This portion of the edge won’t extend out as far as the normal, reeded edge.

If the foreign matter extends past the ridges on the working face of the collar, then this material will stand in the way of any planchet forced down upon it by the impact of the hammer die.  This collision will push coin metal upward from the edge and prolong it into a vertical flange.  The opposite face will show distortion of the rim in the form of a rounded shoulder.

At the moment, obstructed collar errors are known only from a few Canadian specimens.  Here we see the affected portion of a 1999 Canadian dime struck within an obstructed collar.  Coin metal has been scraped from the edge and forced into a vertical flange that is triangular in shape.  The corresponding area on the obverse face (struck by the anvil die) lacks the design rim and instead shows a rounded shoulder