Previous Collectors’ Clearinghouse columns (Feb. 22, 2010; Aug. 22, 2011; Jan. 16, 2012) introduced an unusual form of machine doubling designated “one-sided, rim-restricted design duplication.”
After reaching the lowest point of its downstroke, the hammer die bounces up, shifts laterally and lands lightly on top of the coin’s newly struck design rim. This second impact leaves a duplicate set of peripheral design elements atop the design rim.
Specifying “one-sided” is essential because there are cases in which a second set of design elements appears on both the obverse and reverse design rims. One must sift through multiple working hypotheses when evaluating such unusual cases. Furthermore, one shouldn’t assume that the same explanation will apply to every case.
The illustrated 2005 Lincoln cent exhibits bifacial, rim-restricted letters on the left side. Duplicated obverse design elements include the L of LIBERTY and the upper half of IN GOD WE. Duplicated reverse design elements include the bottom portions of ONE C and the top portions of UN (from UNITED).
By 2005 nearly all cents were being struck by high-speed Schuler presses employing inverted dies (reverse die as hammer die). I would therefore assume that the reverse face of this 2005 cent was struck by the hammer die.
While it’s impossible to be absolutely sure about the events responsible for these extra letters, some scenarios are more likely than others.
Double-sided machine doubling is uncommon but nevertheless well-documented (Clearinghouse, March 15, 2010). The amount of offset displayed by the extra letters of the 2005 Lincoln cent is well within the range of die movements documented in severe cases of machine doubling, but only in those cases generated by the hammer die. The amount of lateral movement required of the anvil die to leave lettering on the obverse rim of the 2005 cent is impossible if we assume the anvil die neck was tightly confined by the collar. A second problem with this scenario is that when machine doubling occurs on both faces it almost always points in different directions.
The extra letters on each face of the 2005 cent are properly aligned relative to each other and show the same degree and direction of lateral offset. This strongly implies that it was the coin that moved and not the dies. A double strike is therefore a much more plausible explanation, leaving only the sequence of strikes to be determined.
Light off-center strike followed by strong in-collar strike:
It’s possible that the faint letters were produced by a very weak, slightly off-center first strike, with the impact primarily felt on the planchet’s proto-rim. This would have been followed by an in-collar strike of normal strength. A planchet struck this weakly would show no significant expansion and would be able to fit back into the collar for a second strike. Planchets with design elements largely or completely restricted to the proto-rim have been reported (Clearinghouse, Oct. 10, 2011, and April 8, 2013). These elements could conceivably persist on top of the coin’s design rim after a normal second strike due to the lower effective striking pressure in this area. However, I would expect the letters to be somewhat flattened from contact with the roof of the rim gutter and this doesn’t appear to be the case here.
Normal first strike followed by weak, slightly off-center second strike:
This appears to be the most convincing scenario. After a normal first strike, the collar presumably failed to deploy and the coin shifted ever so slightly in an east/northeast direction (as seen from above). During the second strike, something prevented the dies from approximating normally so that at their closest approach they only managed to contact the points of highest relief, located on the newly-struck design rim.
Another coin, another explanation:
An outlying crescent of die-struck design replaces much of the design rim on the left side of a 1967 20-centavo coin from Brazil illustrated here. In this case the extra elements are the product of a weak, off-center first strike. The coin was properly centered during the second strike although the collar was only partly deployed (making it a partial collar error). The hammer (obverse) die was misaligned toward the southeast during the second strike, allowing details of the first strike to persist to a greater extent than they ordinarily would have.
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