Several years ago a production run of 2001-P Kennedy half dollars
caused a bit of a stir when it was realized that their cross-sectional
profile mimicked — at a very small scale — a bowl-shaped design. A
similar feature has been adopted for the 2014 National Baseball Hall
of Fame commemorative coins.
The reverse face of an affected 2001-P Kennedy half dollar bulges
out to such an extent that the coin rocks when you press lightly
anywhere along the obverse rim. This is a case of global die
subsidence (a sunken die error that affects the entire die face). The
die steel was abnormally soft and sank in when the die was set to work
striking half dollar planchets. The softness could have any number of
causes: selection of the wrong grade of steel, impurities or
microscopic cavities in the steel, or improper die preparation
(annealing, quenching, tempering).
The reverse die also shows an odd pattern of semi-circular die
cracks that run through the circlet of stars and the arc of clouds on
the reverse face. These cracks may mark the boundary between softer
steel in the center and harder surrounding steel.
Although these half dollars were described in several online and
print publications, only my report in the September/October 2008
Errorscope picked up on the fact that the obverse die was also
deformed. The obverse die bulged out slightly, leaving the obverse
face of each half dollar with an abnormal degree of concavity. I was
only able to detect this subtle deformation because I had available
several of the error half dollars. When the reverse face of a deformed
2001-P half dollar is placed on the obverse face of a normal 2001-P
half dollar, it wobbles. But when it rests on the obverse face of
another deformed half dollar, it is completely stable. This close fit
could only mean that the two dies were reciprocally deformed, stamping
out a succession of convex/concave coins.
The reciprocal deformation would explain, at least in part, why no
centralized weakness is seen in the strike. Ordinarily, if one die
face retreats, effective striking pressure is reduced to such an
extent that details don’t strike up completely (see the 2003-D
Roosevelt dime reported in the Aug. 29, 2011, column). However, if the
opposite die simultaneously protrudes, effective striking pressure is
maintained at an adequate level.
Recently, Steve Rodriguez sent me a 1972-D Kennedy half dollar
that also has a bulging reverse. The coin spins effortlessly around an
elevated center that seems to coincide with the body of the eagle. But
is the bulge due to die deformation or post-strike damage? The coin
provides scant evidence in support of either proposition.
The coin has no centralized weakness in the design. Nor is there
evidence of an impact that would have pushed in the obverse face and
pushed out the reverse face. Then again, subtle basining on a coin is
often impossible to detect, whether it’s due to a bulging die or a
No die cracks are present on either face. The only die
imperfection (other than ordinary signs of die wear) is a light clash
mark of the top of Kennedy’s head on the reverse face. The quality of
the strike is indicative of a late die state.
Reeding is normal and undamaged.
A final clue would be whether the coin is abnormally wide or
out-of-round. Here the evidence tilts in the direction of post-strike
damage. The coin’s north-south diameter is 30.62 millimeters — very
close to the textbook figure of 30.61 millimeters and certainly within
the normal range of variation. However, the east-west diameter is
30.67 millimeters. While deviations from perfect circularity of .01
millimeter to .02 millimeter are common, a difference of .06
millimeter is rather extreme. While I can’t state categorically that
this measurement discrepancy is outside the known range of variation,
it is disturbing.
A reversal of opinion in favor of authenticity would require only
the discovery of another half dollar struck from the same die pair
that also shows a convex reverse. So keep your eyes open.
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