Was this 1972-D half dollar struck by a concave reverse die?

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Published : 09/07/13
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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 “soft” impact.

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.

Coin World’s Collectors’ Clearinghouse department does not accept coins or other items for examination without prior permission from News Editor William T. Gibbs. Materials sent to Clearinghouse without prior permission will be returned unexamined. Please address all Clearinghouse inquiries to cweditor@coinworld.com or to 800-673-8311, Ext. 1722

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