US Coins

Grease-mold doppelgängers novel form of error

The Aug. 19, 2013, column introduced a novel striking error in which a false design element is generated by a mold of stiff, smoothly textured die fill (“grease”). I initially adopted the term “grease-mold doubling” for this phenomenon, but it proved inadequate for those cases in which the false element entirely replaces the true element. So I’ve instead taken to calling the phenomenon “grease-mold replication.” The false element itself can be termed a “replicant” or more whimsically, a “doppelgänger,” the German word for a spectral body double.

Having conformed to the shape of its recess, the stiff mold somehow migrates out onto the adjacent field portion of the die. When a planchet is fed into the striking chamber, the stiff plug of material (presumably convex where it faces the die and concave where it faces the planchet), acts as a micro-die that generates a raised, normally oriented element of very low relief. The accessory element is slightly offset from its normal counterpart and tends to be slightly enlarged and distorted.

At the time of writing, the phenomenon was confined to 1995 Lincoln cents (representing several die pairs) and restricted to the last digit of the date. A photo of one of those cents is reproduced a the bottom of the page. The left side of the normal 5 is visible, although grease in the corresponding recess has left it hazy and flat. The right side of the normal 5 was totally obscured by grease and replaced by a false digit that is offset to the right, rotated slightly clockwise, and is somewhat enlarged.

In recent months I’ve come across grease-mold replicants in Lincoln cents from other years. On March 31 a collector with the username Hogan36 posted an inquiry concerning a 1999-D cent on the Coin Community Forum. The photograph he provided clearly shows that the right half of the last 9 of the date has been replaced by a false numeral that is offset to the right and is larger than the normal digit. As with other examples of grease-mold replication, the grease has blurred or obscured other portions of the design, most notably the IB of LIBERTY.

In early September, Larry Peterson presented a 1998 cent with grease-mold replication on the Lincoln Cent Forum.

His example features a secondary 8 to the right of the normal 8. The accessory numeral is slightly enlarged and is dramatically offset to the southeast. Somewhat surprisingly, the ghostly integer invades a portion of the field that shows no evidence of having been struck through grease. The edge of the mold must have been neatly trimmed, without any slop-over.

Persistent mysteries

The grease-mold theory assumes the presence of a stiff mold within which lies a shallow recess that acts as a micro-die. But if that’s the case, I would expect to see an impression of the mold’s surrounding wall. In other words, there should be a shallow depression surrounding the raised number. I fail to detect any such depression in the examples I’ve examined. It may simply be that the entire apparatus is too thin to leave a discernible recess.

It also strikes me as odd that a raised element is generated in every case. Ordinarily, when a plug of compacted die fill is dislodged from its recess and struck into a planchet it generates a dropped filling. A dropped filling impression is incuse and normally oriented (unless it flips over or comes to rest against the opposite die). Many dropped filling errors have been featured in Collectors’ Clearinghouse, ranging from isolated letters and numbers, to conjoined elements, to expansive fillings involving large portions of the design.

I can only speculate that critical factors involved in grease mold replication include the thickness, stiffness, compressibility, resilience, and texture of the grease mold. Since the dies’ impact generates significant heat, thermal expansion might also be a factor. I find it significant that the incuse numeral in the die face remains filled with grease even after the mold has migrated laterally. In other words, the recess hasn’t been vacated, as is the case with a dropped filling error. This suggests to me that the die fill is not actually dislodged but that it instead swells and overflows its recess. Whether it’s actually possible in such circumstances to maintain the shape of the mold and the necessary stiffness to leave an impression is unclear. But I am unable to devise an alternative mechanism.

Leaving aside the accuracy of the proposed etiology of this phenomenon, one is vexed by associated mysteries. Why, for example, are so few cents affected? Grease strikes involving smoothly-textured die fill are endemic among copper-plated Lincoln cents from the very beginning (mid-1982). The date area is affected as often as any other, yet very few examples show grease-mold replication.

Also unexplained is why the same element is involved time after time. What’s so special about the last digit of the date that it should be targeted in every instance? 

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