PART III. Die installation Errors:

Mules: 

Wrong anvil die

Definition: Mules are coins struck by mismatched dies. In this case the wrong anvil die was installed in a coin press.

This Malaysian 10 sen mule was struck on a 10 sen planchet in a reeded 10 sen collar and carries a normal 10 sen obverse. The reverse face was struck by a 1 sen reverse (anvil) die.

This dual denomination mule was struck in 1993 by the Denver mint. It had the correct hammer die (cent die) and the coin was struck on the correct planchet. However, the anvil die (dime die) was mistakenly installed in the coin press which resulted in this unique combination.

This dual denomination mule coin was struck in 1999 by the Philadelphia mint. It had the correct hammer die (cent die) and the coin was struck on the correct planchet. However, the anvil die (dime die) was mistakenly installed in the coin press which resulted in this unique combination.

Images courtesy of Heritage Auctions

PART III. Die Installation Errors:

Mules: 

Wrong hammer and anvil die

Definition: Mules are coins struck by mismatched dies. In this case both hammer and anvil dies were not correct.

This Malaysian mule would be classified as a “double mule” It was struck by a 1 sen obverse die and a 1 sen reverse die installed in a 10 sen press. The coin was struck on a copper-nickel 10 sen planchet inside a 10 sen collar and shows the reeded edge normal for the 10 sen denomination (the 1 sen coin has a smooth edge).

PART III. Die Installation Errors:

Mules:

Wrong hammer die

Definition: Mules are coins struck by mismatched dies. In this case, the wrong hammer die was installed in a coin press.

The 2005 Malaysian mule shown below was struck on a copper-nickel 10 sen planchet inside a reeded 10 sen collar and features a normal 10 sen reverse design. The obverse (struck by the hammer die) shows an unexpected and appreciably smaller 1 sen design. This resulted in a weakly struck periphery on the reverse face. A normal 1 sen coin is copper-plated steel.

PART III. Die Installation Errors:

Mules: 

Regular-issue die muled with commemorative

die, September and November 1999

Canadian quarters

Definition: Mules are coins struck by mismatched dies.

Two 1999 mules from Canada’s Millennium series fall into this category. A September 1999 quarter and a November 1999 quarter pair the intended commemorative reverse (hammer) die with an incorrect obverse (anvil) die that was supposed to strike ordinary quarters with a caribou reverse. As a result, the coin carries no denomination. Thousands of each were produced.

PART III. Die Installation Errors:

Mules: 

Mule die larger than normal die and collar

Definition: Mules are coins struck by mismatched dies.

The unique 1995 cent/dime mule struck on a dime planchet inside a dime collar fits this description.

PART III. Die Installation Errors:

Mules: 

Mules involving pattern dies, various types

Definition: Mules are coins struck by mismatched dies.

This is a broad category (a genus?) that could encompass a variety of mule species. While little knowledge exists of any standard dies being paired with a pattern die, two possibilities are shown below.

PART III. Die Installation:

Mules: 

Pseudo-mules

Definition: A coin with the same raised design on each face, but which is struck with a pair of conventional dies.  Pseudo-mules can be generated by accident or by intent.  There are three ways a pseudo-mule can be generated.  For purposes of this discussion, we’ll describe a pseudo-mule that carries the design of the hammer die on each face.  An example would be a two-headed cent from the 1980’s (before inverted die installation was introduced by the U.S. Mint).

Method 1. A coin flips over on top of a planchet, landing within the collar or in a perfectly centered position. The
two discs are struck together. The original die-struck hammer die design is flattened. The original die-struck anvil die design is obliterated by the force of the strike. The double thickness causes an increase in effective striking pressure, which facilitates erasure of the anvil die design.

Method 2. Two planchets are struck together within the collar, producing two in-collar uniface strikes. The bottom coin is ejected while the top coin flips over and lands on another planchet. During the second strike, the original hammer die design is flattened, while the original featureless surface is struck by the hammer die.

Method 3. The sequence begins with a coin with an in-collar, first-strike brockage of the hammer die design on the face normally struck by the anvil die. The coin flips over and lands in the collar. A planchet is fed on top of it and then struck. The top coin has on its bottom face a first-strike counterbrockage of the hammer die design.

A 2005 Malaysian 1 sen coin shown below carries the obverse design (struck by the hammer die) on each face. It is an intentionally fabricated, double-struck pseudo-mule. Method 2 was almost certainly employed.

PART III. Die installation Errors:

Mules: 

Wrong anvil die

Definition: Mules are coins struck by mismatched dies. In this case the wrong anvil die was installed in a coin press.

This Malaysian 10 sen mule was struck on a 10 sen planchet in a reeded 10 sen collar and carries a normal 10 sen obverse. The reverse face was struck by a 1 sen reverse (anvil) die.

This dual denomination mule was struck in 1993 by the Denver mint. It had the correct hammer die (cent die) and the coin was struck on the correct planchet. However, the anvil die (dime die) was mistakenly installed in the coin press which resulted in this unique combination.

Images courtesy of Heritage Auctions.

This dual denomination mule coin was struck in 1999 by the Philadelphia mint. It had the correct hammer die (cent die) and the coin was struck on the correct planchet. However, the anvil die (dime die) was mistakenly installed in the coin press which resulted in this unique combination.

Images courtesy of Heritage Auctions

PART V. Planchet Errors:

Lamination:

Lamination Fold-over Before Strike

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.

The image above shows a 1964(P) Lincoln cent with a semi-lunar (half-moon shaped) lamination flap that lifted up from the edge of the coin and folded over onto what would eventually become the obverse face of the coin.

PART V. Planchet Errors:

Lamination:

Lamination Cracks

Definition: Lamination errors are planchet errors in which the surface of a coin cracks and flakes.  It is generally believed that lamination errors are caused by contaminants in the alloy that cause the metal to separate along the horizontal plane.   Lamination errors can develop before or after the strike.  They are generally restricted to solid-alloy coins.  The term “lamination error” is grammatically incorrect as the metal is actually delaminating.  While “delamination error” would be the proper term, we’re stuck with the terminology we’ve inherited from previous researchers.

Lamination errors are closely related to split planchets and clam-shell splits.  In the latter two errors, separation also occurs in the horizontal plane, but at a deeper level.

A lamination crack is one common manifestation of a lamination error.  The surface of the coin simply cracks and may lift up slightly on one side.  Lamination cracks are sometimes mistaken for die cracks and split dies by novice collectors.

This 1954 Roosevelt dime shows a lamination crack crossing the President’s head.