Among the rarest of all errors are two-headed and two-tailed mules
(mules are coins struck by mismatched dies).
Only one double-obverse (“two-headed”) mule is known among U.S.
coins — an 1859 Indian cent. Only three known double reverse
(“two-tailed”) mules are known — two copper-nickel clad quarter
dollars and one copper-nickel clad dime.
These mules owe their existence to the accidental or intentional
installation of two hammer or two anvil dies. But at least three other
pathways can lead to a two-headed or two-tailed coin, and none require
mismatched dies. One pathway is illustrated by an undated Jefferson
5-cent coin provided by Scott Taylor.
The first strike was normal. What initially looks like a second
strike is 90 percent off-center and carries raised, normally oriented
obverse design elements on each face. The two designs are almost
perfectly aligned in vertical space.
Numerous clues demonstrate that the off-center designs were not
generated by a muled pair of obverse dies. Next to the centered
obverse face, the off-center strike is strongly convex and shows a
matte texture. Design elements on this face are slightly expanded and
flattened. All these clues indicate that this area was struck against
another planchet. Finally, die markers are identical on the centered
obverse face and the crisper of the two off-center obverse designs.
This 5-cent coin exhibits an off-center pseudo-mule (false mule)
struck in a press with a normal die set-up. It required three strikes.
After a normal first strike, it received a 90 percent off-center
second strike that was uniface (struck against an underlying
planchet). It then flipped over and received a third off-center
strike, which was also 90 percent off-center, also uniface and
directly on top of the second strike.
Pseudo-mules are much more compelling and deceptive when the two
obverse or reverse designs are complete. The illustrated 2005 Malaysia
1-sen coin is a pseudo-mule that carries the obverse (hammer die)
design on each face. Two steps were necessary to create it.
In the first step, two planchets were placed together in the
collar and struck. The top coin was left with a die-struck obverse
design and a featureless reverse face. Such an error can occur
naturally and is called either a “uniface strike” or a “full indent.”
The coin was then flipped over and placed back into the collar on top
of a fresh planchet. When the two discs were struck, it left the top
coin with a fresh die-struck obverse design on the original
featureless surface. The original die-struck obverse face was
flattened from where it rested on the planchet during the second strike.
Many similar 1-sen pseudo-mules emerged around this time period
and are clearly intentional errors. Several have been erroneously
encapsulated by Professional Coin Grading Service as double-obverse mules.
A double-reverse pseudo-mule can be created in the much the same
way. One simply uses the bottom member of an in-collar uniface pair.
Flip it over, place a fresh planchet on top it, deliver a second
strike, and you’ve got two reverse designs (one flattened, of course).
A pseudo-mule doesn’t even require two uniface strikes in
sequence. A simpler scenario involves a normal coin flipping over and
landing perfectly on top of (or beneath) a fresh planchet. The two
discs are then struck together in- or out-of-collar. The increased
effective striking pressure generated by two stacked discs is
sufficient to obliterate the original design on the face struck
directly by one of the dies.
This kind of pseudo-mule error will generate a perfectly centered,
flip-over, first-strike brockage on the planchet that rests against it.
A final sequence of events requires only a single strike to be
delivered to the planchet that will become the pseudo-mule. In this
scenario, a coin with an in-collar, first-strike brockage flips over
and lands beneath or on top of a fresh planchet. When the two discs
are struck together (in- or out-of-collar), the brockaged coin acts
like a die and generates a raised, normally oriented design — a
counterbrockage. I have not yet encountered this type of pseudo-mule.
However it’s produced, a pseudo-mule will have the raised design
flattened on one face. If struck out-of-collar, it will often assume
the cupped shape of an anvil or hammer die cap, with the design on its
“working” face grossly expanded and distorted.
Have any domestic pseudo-mules been mistakenly encapsulated as
true mules? Possibly. A third encapsulated two-tailed quarter dollar
is known, but this one was double struck in-collar, the second time
against an unstruck planchet. One face is correspondingly flattened
and distorted. While Numismatic Guaranty Corp. claims the coin was
struck by two reverse dies, its appearance is equally consistent with
that of a two-tailed pseudo-mule produced in a manner described earlier.
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