In a normally functioning coinage press, planchets are fed into the
striking chamber one at a time. But once in a while, two planchets are
fed in together in such a way as to perfectly overlap each other.
The strike converts the two coins into a pair of complementary
uniface strikes. The facing surfaces of the two coins end up with no
design. Each error coin is designated a “full uniface strike” or a
The only kind of uniface strike that most collectors are familiar
with — and the only one that grading services typically recognize —
are those struck fully within the collar. These are usually termed
“in-collar uniface strikes.”
The undated Roosevelt dime shown here is a typical example of a
uniface error struck fully within the collar. The featureless obverse
face is not flat like a pane of glass, but instead shows gentle
undulations. The undulations are actually faint ghost images — an
incuse suggestion of the reverse design and a raised suggestion of the
obverse design. It should be noted that not all in-collar uniface
strikes display recognizable ghost images.
In-collar uniface strikes derived from the bottom planchet are
often confused with the early strikes of a uniface die cap. The
illustrated Jefferson 5-cent coin depicts the latter error. A key
difference is the presence of a gently sloping “wire rim” in the
latter example. A uniface die cap starts out as a uniface strike but
then sticks to the die and strikes additional planchets.
In-collar uniface strikes derived from the top planchet are rarer
than those derived from the bottom planchet. The anvil die has to be
recessed to an unusual degree to accommodate two planchets of normal
thickness. The undated State quarter dollar shown here is a promising
candidate, given that the obverse design is die-struck. However, some
State quarter dollars were struck with the obverse die serving as the
hammer die and others with it as the anvil die. There’s no way to be sure.
Uniface strikes that are also broadstruck (struck out-of-collar)
are probably more common than in-collar uniface strikes, at least
within the population derived from the bottom planchet. The undated
broadstruck Lincoln cent depicted here is a representative example of
this error type. The obverse face is featureless while the reverse
face (not shown) is die-struck. Such errors are frequently — and
mistakenly — encapsulated as “reverse die caps” by leading grading services.
The counterpart to this coin is, of course, a uniface strike with
a die-struck obverse design. These usually curl up toward the hammer
die when struck, creating a cap-like appearance. An example of such an
error is shown here in the form of a 1991 Lincoln cent. Such coins are
consistently and erroneously encapsulated as “obverse die caps.”
There’s no indication that this 1991 cent was struck more than
once. A smooth transition exists between the featureless reverse face
and the upturned wall. Had it struck another planchet (thereby
becoming a uniface die cap) the transition zone would likely have
shown a subtle disruption.
Internally, the coin features a single set of fine radial
striations in the “slide zone” extending from the margin of the
die-struck field to the edge of the coin. Had there been more than one
strike, it is likely that the radial lines would have been interrupted
by concentric strike lines.
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