Part VI. Striking Errors:

Excessive Striking Pressure:

Stretch Strikes (Die-Struck on Both Faces)

Definition: A stretch strike is an off-center strike with a very wide “slide zone”.  Uniface strikes (coins struck against another planchet) often take the form of a stretch strike because the double thickness greatly increases effective striking pressure.  Stretch strikes are rarer when only one planchet is involved.

A stretch strike that is die-struck on both faces owes its existence to an abnormally small minimum die clearance.  Minimum die clearance refers to the minimum distance between the dies at their closest approach in the absence of a planchet.  A stretch strike can also reflect elevated ram pressure, but this is hard to prove.  Ram pressure is the tonnage delivered to a planchet of normal thickness.  Elevated ram pressure without an accompanying reduction in minimum die clearance will not result in a stretch strike.

In addition to the wide slide zone, a stretch strike will also show exaggerated metal flow in peripheral design elements.

PART IV. Die Errors:

Collar Cuds: 

Retained Collar Cud

With this type of collar break, part of the collar breaks off but does not fall away. Instead,  it remains close to the intact part of the collar. It may be that the hardened working face of the collar breaks off and sinks into the surrounding softer metal.  Or it may be that one side of the collar breaks away but is held in place by bolts or clamps or whatever anchors the collar to the press frame.

Although it’s sometimes difficult to distinguish from a bilateral split collar, there are some telltale diagnostics. A bilateral split collar shows only horizontal spread. This creates a raised nib at both poles (see bilateral split collar),
but the curved outline of the coin is largely undisturbed except for the fact that the original circle is converted to a modest oval. With a retained collar break you look for evidence of vertical movement, horizontal offset, or pivoting – something that indicates unusual mobility in part of the collar. Diagnostics to look for are as follows:

1. Evidence of collar contact on both sides of the break at one or both endpoints. Collar contact will be seen along most of the edge that lay adjacent to the mobile side of the collar.
2. A step-up at one endpoint and a step-down at the other endpoint. This may indicate a pivoting movement of the detached portion of the collar or it could mean the presence of horizontal offset (a sliding movement in the direction of one endpoint). Both patterns of movement can of course be present.
3. A partial collar “step” that occupies a different height on either side of the break. This indicates vertical movement.
4. A partial collar that slopes down (or up) on one side of the break at a different angle from the other side of the break. This indicates the presence of tilt on the loose half of the collar

Depicted below is a 1973-D cent with a retained collar break on the right side. With diagnostics 1 and 2 present the endpoints are 180 degrees apart and can be seen at 1:00 and 7:00. There is clear evidence of collar contact on either side of the break at the upper endpoint, and clear evidence of collar contact along much of edge along the right side. There is a step-up at 1:00 and a step-down at the 7:00. It’s probably indicative of horizontal offset since expansion on the right side is symmetrical. Pivoting is associated with uneven expansion that’s greater toward one endpoint. A collar chip lies along the right side of the break at the 1:00 position. It extends from one rim to the other.

Part IV. Die Errors

Die Breaks:

Retained Cuds:

Retained Cuds of Hammer Die

Definition: A retained cud is a fragment that breaks off the edge of the die but is nevertheless held in place. Retained cuds are rarely found in connection with the hammer die.  That’s because gravity usually insures that the fragment falls out and is lost.  It’s been said that the fragment is held in place by the bolts or clamp that secure the hammer die in its recess within the die assembly.  But this cannot be the case because the die neck (where retained cuds form) is free.  It is the die shaft and base that are tightened down.  There must therefore be another mechanism responsible for retained cuds of the hammer die.

The vast majority of claimed retained cuds of the hammer die are probably invalid.  Most of these alleged retained cuds were probably still connected to the rest of the die neck.  Slight to moderate displacement is likely due to subsurface deformation beneath a cracked die face.

In cases of severe horizontal displacement, it’s possible that the die fragment breaks free, shifts position, and then fuses to the roof of the void during the next strike.

This cent represents a reasonably good candidate for a retained cud of the hammer die (in this case the obverse die).  The island of design at the base of Lincoln’s bust shows a great deal of lateral spread and horizontal offset.  The amount of vertical displacement is slight, however.  If this is a true retained cud, it’s likely that the die fragment fused to the roof of the void after breaking free and shifting position.  If not, then we can assign the movement to subsurface deformation.

Part IV. Die Errors:

Die Breaks:

Cuds:

Retained Cuds:

Retained Cud that Protrudes Beyond Die Face

PART IV. Die Errors:

Retained Interior Die Breaks: 

Connected to die crack or split

Definition: A retained interior die break occurs when a flake detaches from the die face but, instead of falling off, it
sinks into the surrounding metal.

Depicted below is a large, retained interior die break straddling a split die in an uncirculated 1973-D nickel. Part of Monticello (the building, not the motto) is raised up on a pedestal, and there is an abrupt step-down to the rest of the design. Essentially, the split diverged around the flake at one end, and reunited at the other end. Of course, deep to the flake, the split would have to have been continuous. The flake would probably have been somewhat wedge-shaped if sectioned vertically from north to south. After breaking free, the flake sank into softer surrounding metal, leaving a corresponding raised area on the coin.

PART V. Planchet Errors:

Alloy Errors:

Lamination: 

Retained Lamination

Definition: A lamination error occurs when metal flakes off the surface of a coin or planchet.  It is generally believed that the flaking, peeling, and cracking is due to impurities in the alloy which causes metal to separate along horizontal planes of weakness.

A retained lamination error is a flake that remains attached to the main body of the coin.

Part IV. Die Errors:

Die Breaks:

Cuds:

Rim-to-Rim Cuds

Definition:  A large flake spalls off the die face, connecting two points on the rim.  This is the rarest type of cud.

PART VI. Striking Errors:

Machine Doubling:

Push Doubling:

Definition: Push doubling occurs when a die bounces off the surface of the coin, shifts position, and lands lightly in a different spot.  A diagnostic feature is marginal shelving at the edges of design elements.  Interior features often show rounded doubling that is easily mistaken for the effects of a double strike or a doubled die.  Push doubling can occur on either face, although its most dramatic expressions tend to appear on the face struck by the hammer die. Cases of push doubling can involve up to three closely-spaced sets of accessory design elements.  Push doubling can occur on both faces simultaneously and often in different directions.  Up to three different doubling directions can be represented on a single face.

Forms of machine doubling combining elements of both push doubling and slide doubling do occur.

Classic machine doubling can be seen on this 1991 Lincoln cent.  The doubling occurs on both faces.  The obverse face shows doubling in three different directions — east-to-west, south-to-north, and north-to-south.

The illustration first shows shows a in collar rotated double strike on a token where the black arrows show the first strike of CA, subsequently flattened, the hammer die retracted then struck a second time and the red arrows show the CA from from that strike. The red arrows show areas from the first strike that were not impacted from the second. At the bottom is push doubling where the green arrows show the RTY and then the violet arrows where die rebounded and flattened part of the devices.

PART IV: Die Errors

Die Deterioration/Deformation Errors:

Reciprocally Deformed Convexo-Concavo Dies

Definition: This rare error occurs when one die face sinks in and the other bulges out in a complementary fashion.  The effect can affect the center of the die face or the edge of the die face.  The affect can be global (affecting the entire die face) or local.

The only known case among domestic coins is found in a production run of 2001-P half dollars.  The dies show a pattern of global, centralized deformation.  The reverse die sank in while the obverse die bulged out.

The images below show one of these half dollars.  The reverse face bulges out noticeably, and the coin spins effortlessly around the highest point of that bulge, which lies in the center of the reverse face.  Semicircular die cracks run through the ring of stars and the clouds that lie above the eagle.  These cracks probably mark the edge of the zone of subsidence.

The obverse face is more concave than normal, although the effect is subtle.

A second case of reciprocal die deformation has been recorded in an off-center 2007 India 2 rupee coin (see photos below).  Here the deformation is restricted to the right side of the reverse (hammer) die and the corresponding left side of the obverse (anvil) die.  The periphery of the reverse die assumed a concave cross-sectional profile, leaving the reverse face of the coin with a convex surface on the right side.  The periphery of the obverse die assumed a convex cross-sectional profile, leaving the obverse face with a concave surface on the left side.

The downwardly inflected edge of the reverse die cut deeply into the planchet.  The upswept perimeter of the obverse face meets the unstruck portion of the planchet in a more gentle fashion.  The unstruck crescent on the left side of the obverse face has a very deep, very irregular collar scar, indicating that the collar was damaged.  This coin also shows a horizontal misalignment of the obverse (anvil) die.  This indicates that either the collar broke free of its moorings or that it broke apart, freeing the anvil die of its embrace.

PART II. Die Varieties:

Repunched Mintmark (RPM)

Definition: A repunched mintmark variety is generated when the letter punch that is used to punch the mintmark into the working die leaves two or more offset impressions.  The impressions almost always overlap.  A totally separate secondary mintmark is a rarity.

The secondary mintmark is usually thinner and smaller than the normal mintmark.  This is due to the fact that the apex of the raised letter on the letter punch is narrower than the base.  In other words, the raised letter on the letter punch tapers in vertical cross-section.

Repunched mintmarks can reflect any of the following mishaps: