MINT ERRORS

MINT ERRORS

When we speak of mint errors, some people will think of doubled dies (DDO’s & DDR’s), re-punched mint marks (RPM’s), and over mint marks (OMM’s).  Doubled Dies are errors related to die creation whereas RPM’s and OMM’s are human errors cause by the manual process adding a mint mark to an existing die.  These are not considered mint errors. 

So what exactly are ‘mint errors’…?  Mint errors are a malfunctions of the striking process.  There are many different types of errors.  Let’s go through some of them.

BROADSTRIKE  – A coin that is struck outside the collar.  The collar is the retaining ring that establishes the final diameter of the newly struck coin.  A broadstrike will expand beyond the diameter of a normal coin, sometimes drastically so. In order to qualify as a broadstrike, the full design must be present on both faces.  If the design is cut off on either face, it is called an off-center strike.

BROCKAGE – A brockage is an incuse, mirror image version of the coin design.  It is produced when a coin is struck into a planchet or another coin.  A full brockage is one that covers the entire face (obverse or reverse).  The coin carrying the brockage can be struck inside or outside of the collar.  The brockage can be complete or incomplete.  The first impression of a coin is called a first-strike brockage.  If the coin sticks to a die and becomes a die cap, it will strike additional planchets.  These later impressions are called ‘early-stage’, ‘mid-stage’, and ‘late-stage’ brockages.  The sharpest, most complete first-strike brockages occur when both the coin (the brockage-maker) and planchet are confined by the collar.  These ‘mirror-brockages’ are highly sought after.     

CLASHED DIES – This mishap occurs when opposing dies collide with each other when a planchet fails to be fed into the striking chamber.  Most complete planchet misfeeds don’t result in clashed dies because dies normally don’t touch each other in the absence of a planchet.  The dies operate with a safety margin that can be referred to as minimum die clearance or minimum die distance.  These terms refer to the closest approach the dies make to each other in the absence of a planchet.  In order for dies to clash, the dies must have fallen out of adjustment so that their minimum clearance is zero (or less than zero).

CLIPS – Clipped coins are errors which begin when punching blanks from the rolls of copper plated zine, nickel, or clad coins.  While these can be thought of as an error related to the punching process, they still make it to the feeder bins from where the coins are struck.  The different types of clips are: 

• Curved Clip – these are generated when the punching process overlaps a previously punched hole in the metal strip.
• Elliptical Clip – these are caused when an off center planchet becomes trapped between the descending hammer die and a collar “frozen” in the up position.  As a result, the trapped planchet is sheared in two. The portion of the planchet protruding outside the striking chamber becomes a curved (and often crescentic) strike clip.  The portion remaining in the striking chamber becomes an elliptical strike clip, giving the finished coin a football like shape.
• Ragged End Strip Clip – these are believed to be derived from the unfinished leading or end of the metal coin strip.
• Straight End Clip – these are believed to be derived from the leading or end of the metal coin strip.        

CUDS – A cud is a die break that involves the rim and at least a little bit of the adjacent field or design.  The vast majority of sizable die breaks are cuds.  Cuds can assume a wide variety of shapes including ovoid, crescentic, and irregular.  Most cuds represent spontaneous brittle failure.  A small minority arise as the result of impacts.

DIE CAPS – A die cap begins when a coin sticks to a 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 phenomenon is called ‘cupping’.  Eventually the die cap assumes a thimble shape.  Any design originally present on the working face of the die 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. (See struck through below.)   

DOUBLE DENOMINATIONS – A coin struck for a second time by dies belonging to a different denomination.  These are highly sought after and valuable.  

DOUBLE STRUCK – These coins are the result of a failure of the ejection process from the striking chamber resulting in the same coin being struck two or more times.

FILLED DIES – Also known as ‘struck-through’ coins, these coins are generally created when a grease buildup in the die hardens, thereby removing the details in that area.  The most recently publicized version of such a coin was the 2005 Kansas State Quarter whose obverse read:             ‘IN GOD WE RUST’.   

INDENTS – An indent is defined as an indentation from an unstruck blank or planchet.  Any other kind of indentation is referred to as a ‘struck-through’ error.  Since most indents only cover part of a coins surface, the term ‘indent’ usually refers to a partial indent.  Full indents are, however, referred to as ‘full indents’ or ‘full uniface strikes’.

LAMINATION ERRORS – These errors are observed by cracks or flaking on the surface of a coin.  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.   

MISSING CLAD LAYER – During the bonding process, two outer coils of thin clad strip (75% Cu / 25% Ni) are bonded to the middle coil of a thick strip composed of pure copper.  If the leading end of one of the clad strips lags behind the other two strips during insertion into the bonding mill, the leading end of the composite strip will have only two layers instead of three.  Likewise, if one clad strip terminates prematurely at the trailing end of the bonded strip, that trailing end will only have two layers, one of copper-nickel and one of pure copper.  In each case, the bilaminar section of strip will be rolled to full thickness.  Any blank punched out of that section of the strip will also weigh the same as a normal coin.

A normal-weight missing clad error will also result when a large gap is present of opens up within one of the clad strips.  This gap will be filled by the copper core during bonding and subsequent rolling.

OFF CENTER – These coins are produced when a coin is struck once, albeit off-center.  Unlike a broadstrike, the die does not hit the center of the planchet, but rather the edge.  This gives the coin a freakish appearance with various amounts of the planchet visible.

PARTIAL COLLAR STRIKE – Coins struck in a partially deployed collar.  A partial collar error is one in which the planchet is only partially confined by the collar.  The lower half of the edge shows contact with the working face of the collar while the upper half is smooth, beveled, or both.

A collar can occupy a partially deployed condition for two reasons:

1. It might have been depressed part of the way toward the anvil die face by the pressure applied by a tight-fitting or poorly centered planchet (backed by the hammer die).
2. It might never have occupied a fully elevated position.  Its deployment may have been blocked by a poorly centered coin (in presses where the anvil die is fixed and the collar moves up and down).  Its deployment may have been interrupted for other reasons, such as debris getting trapped between the collar and the anvil die neck.

PLATING ERRORS – Occurs when a zinc planchet is only partially, or possibly not at all, coated with copper in the plating bath.  As a result, some or all of the zinc core remains exposed.

ROTATED DIES – These errors are generally caused when one of the dies spins around on its vertical axis.  In the case of a normal, in-collar rotated die error, it is impossible to determine which die has rotated. 

Rotated die errors can come about in at least three ways:

1. A die can be installed in the wrong orientation relative to the opposite die.
2. The ‘flat’ on the shank of the die can be ground in the wrong spot relative to the design on the die’s working face.  This leads to improper installation.
3. A die can work its way loose and rotate.

Die rotation errors can be stable or dynamic.  Stable rotated die errors produce coins that show the same amount of rotation in each coin that is struck.  A dynamic rotated die error is one in  which the die slowly spins or oscillates on its vertical axis so that most of the coins it strikes show a different amount of rotation.

SPLITS – Split planchet errors are normally restricted to planchets composed of a single alloy.  Cents and nickels are the most commonly affected denominations.  A coin struck on a split planchet will always weigh less than a normal coin.  There are two variations of split coins:

1. BEFORE STRIKE: Coins struck on a split-before-strike planchet will show a pattern of striations on the split face.  The texture of the striations vary from coarse to fine.  If a strike is unusually strong, most of the striations may be effaced.  However, most split-before-strike planchets show a weak strike, because the thinner planchet is closer to  minimum die clearance.
2. AFTER STRIKE: Coins struck on a split-after-strike planchet will exhibit a normal strike on one side of the coin with a muted, striated, ghost-like image of both obverse and reverse on the other side. 

STRUCK THROUGH – Anything which is struck into the coin, but is not retained, is a strike through error.  If the item is retained, it is known as a retained strike through error.  Examples of struck through items include cloth, grease, screws, wires, or any of the many parts of the machinery used to strike coins.  These are highly collectible and valuable.

STRUCK THROUGH CAPPED DIES – Coins struck through a die cap will show a ‘strong ghost’ of the raised design (see Die Cap above). 

STRUCK ON WRONG PLANCHET – A wrong planchet error is exactly what the term indicates – a coin struck on a planchet intended for another denomination (domestic or foreign).  The incorrect planchet may have the same composition (e.g. a quarter struck on a dime planchet) or it may be a different composition (e.g. a quarter struck on a nickel planchet). 

An off-metal error is a coin struck on a planchet whose composition does not match the composition that normally characterizes the coin (e.g. a Presidential Dollar struck on a clad planchet.)

TAPERED PLANCHETS – A tapered planchet is one that thins out at one pole due to a mishap in the rolling mill.  These errors are invariably underweight.  There are a number of hypotheses to explain these errors. 

The best theory I have seen is that these errors originate from the leading or trailing end of the metal strip.  The leading edge may be intentionally thinned for easier feeding into the rolling mill. Alternatively, the leading or trailing ends may be thinned due to decreased resistance to the pressure of the rollers; this would hinge on a failure of the mechanism that maintains the gap between the rollers.

UN-STRUCK PLANCHETS – Also known as ‘Type II Planchets.  These are metal disks (or a blanks) that have passed through the upset mill.  This process smooths the edge of the blank and produces a low proto-rim.

Most unstruck planchets result from complete planchet misfeeds.  The feeder mechanism malfunctions so that the planchet is either not pushed into the striking chamber or it is pushed beyond the striking chamber.