PART VI. Striking Errors:

Struck Through Errors:

Struck Through “Grease”

Definition: The recesses of a die sometimes become clogged with compacted gunk generally composed of a mixture of lubricant, metal dust, and dirt.  This material is sometimes called “die fill” but is more commonly referred to as “grease”.  Die fill can be coarse or smooth, hard or viscous.  It can fill isolated design elements (a “filled die” error) or can coat the entire die face.  Coatings are sometimes so thick that the entire design is obscured.

The image below shows a 1984 Lincoln cent with the obverse and reverse design partly obscured by “grease”.

Here is another example of a Lincoln cent struck through grease fill which obscured both obverse and reverse of the coin. This coin is in the collection of Andrew Kezeli.

PART V. Planchet Errors:

Bonding / Bonding Mill Errors:

Struck Clad Layer:

Split Off After Strike

Definition: A clad layer will sometimes separate from a coin after the strike.  The detached clad layer will show a normal die-struck design on its outer face, and blurred incuse, mirror-image version of the same design on its inner face.

As a practical matter, it is almost impossible to distinguish this error type from clad layers that are struck together with a normal planchet.

An undated clad layer from a Roosevelt dime is shown below. It may have separated after the strike or it may have been fed into the striking chamber beneath a normal planchet.

PART V. Planchet Errors:

Wrong Planchet and Off-metal Errors:

Struck on Emery Discs

PART VI. Striking Errors:

Capped Die Strikes:

Struck Through a Late Stage Die Cap

Definition: A coin struck through a late-stage die cap will show a strong “ghost image” of the raised design (see Die Cap).  Most such errors involve die caps affixed to the hammer die, so we’ll focus on those.

A hammer die cap begins when a coin sticks to the hammer die.  That coin proceeds to strike a succession of planchets.  As it does so the coin expands and its margins grow upward to surround the die neck.  This phenomenonis called “cupping”.   Eventually the die cap assumes a thimble shape.  Any design originally present on the working face of the die cap grows progressively fainter and more distorted.  Eventually no design is left and all you have is a thin cap bottom that has molded itself to the recesses of the die face.

The blurred design seen on a coin struck through a late-stage die cap has bled through the thin floor of that die cap.  We refer to such coins as a “late-stage capped die strike” or a “generic capped die strike”.  The shorter term “capped die strike” is sometimes used.  However, this term is actually non-specific and can encompass any type of capped die strike, including those that feature brockages, counterbrockages, or a mixture of the two.

There’s no telling whether a late-stage die cap was originally striking brockages, counterbrockages, or started out with no design at all (a uniface die cap).  Therefore, calling a featureless capped die strike a “brockage” or a “late-stage brockage” is not accurate.

The images below show three coins struck through late-stage die caps. No  identifiable design elements have been transferred from the working face of the die cap.  Any design originally present on the working face of the cap would have long ago been erased by the numerous impacts against a succession of planchets.  The obverse design has bled through the thin floor of the cap to produce what has generally been referred to as a raised “ghost image”.  The raised design is muted, distorted, and somewhat incomplete.

The last coin to the right shows the results of being struck through the thinnest of die caps. Only wisps of deformation can be seen above the date and LIBERTY.

PART VI. Striking Errors:

Struck Through Errors: 

Struck Through Hardware

Definition: When it comes to foreign objects finding their way into a coinage press, almost anything goes. Bolts, screws, washers, and machine parts such as a feeder finger are occasional targets. Any coin trapped between a die and any of these objects is severely traumatized.

This off-center 1982 cent was struck through a threaded bolt on the left side. The left side of the coin was pinched off and lost as a result of the impact.

Coin courtesy of Sean Reynolds.

PART V. Planchet Errors:

Struck On ‘Aluminum’ Feeder Fingers

Definition: A coin that is struck on a feeder finger.  For U.S. coins, only aluminum or aluminum alloy feeder fingers are known to be involved.  World coins have been struck on feeder fingers of many different alloys.  U.S. coins are struck on “breakaway” feeder fingers that are designed to break off if struck by the dies.  Coins struck onfeeder fingers can represent a strike on what was an intact feeder finger or a strike on a feeder fingerfragment that broke off shortly before the strike was delivered

This 2007(?) John Madison dollar coin was struck twice on aluminum feeder fingers.

PART VI. Striking Errors:

Struck Through a Foreign Object:

Struck Through a Clad Layer

Definition: This error type occurs when a detached clad layer  and an intact planchet enter the striking chamber together. The ensuing strike leaves one face with a shallow indentation and blurred design details in the floor of the indentation.

The 1969 Kennedy half dollar pictured below was struck-through a clad layer that entered the striking chamber on top of the planchet represented by this coin. Coverage was incomplete, leaving the coin with a large, shallow indentation and blurred design details.

Images are courtesy of Heritage Auctions.

PART VI. Striking Errors:

Struck Through Foreign Objects:

Struck Through Dropped Filling:

Isolated Element (number, letter, etc.)

Definition: This error type occurs when compacted die fill (“grease”) falls out of a recess in the die face and onto a planchet.  The plug of hardened material is then struck into the planchet, leaving an incuse impression of whatever design element the plug had molded itself to.  Letters (“dropped letters”) and numbers (“dropped numbers”) are the most common elements duplicated in this fashion.  If the plug remains next to the same die it fell out of, and if it doesn’t flip over, the dropped letter/number is oriented the same way as its normal raised counterpart.  If, however, the filling falls against the opposite die or flips over, the impression is mirror-image.  Most dropped fillings are normally-oriented.

This 1965(P) Lincoln cent shows a dropped letter A near the right base of the Memorial (black arrow). This dropped filling is from one of the three As found on the reverse die.

A more unusual dropped filling is found on this 2006(P) Lincoln cent. One of the urns on either side of the steps of the Memorial filled up with hardened “grease” and then dropped out. It landed on the stairs upside down and was struck into the planchet (black arrow). This dropped filling was verified by the use of overlays.

PART VI. Striking Errors:

“Struck-Through” Errors:

Struck Through Miscellaneous Foreign Matter:

Struck through metal dust or shavings

Definition: A wide range of foreign objects, from large to microscopic can end up being struck into planchets and coins.  Metal dust is a common contaminant in coinage presses and generally leaves tiny, irregular pits in the coin’s surface.  However, if the metal is of a different composition and color, and if it’s retained, it can easily be seen under a microscope.  When it’s combined with lubricant and dirt, metal dust contributes to a compacted, hardened form of “grease” that is frequently struck into coins.

Metal shavings are also sometimes struck into coins.  These can be broken off rim burrs, many of which are produced a split second before the strike by the feeder mechanism.  Other metal shavings will have different origins from elsewhere in the press and from earlier stages in the minting process.  Impressions of metal shavings are generally curved and fang-like.

This 1945-P Lincoln cent was struck through an irregular foreign object which entered the striking chamber at the same time as the planchet that is represented by this coin. The object may have been a shaved-off rim burr.