The following is the Collectors' Clearinghouse column from the Aug.
15, 2016, issue of Coin World:
The hammer die is designed to move vertically during its downstroke
(which culminates in the strike) and during its retraction phase.
Horizontal movements are undesirable and can leave behind a host of errors.
Horizontal movements can occur before impact, during impact, and
during retraction. If a lateral shift occurs during impact or early in
retraction (before it’s cleared the coin’s surface), the die will drag
itself across the coin. This will cause the newly struck design to be
repositioned, smeared, scraped or erased. Effects will also vary
depending on whether the movement occurs in the course of a single
strike or during a second strike.
A skidding die can shift to one side as it’s being driven into the
planchet. This effect can be seen on two 1999-D Jefferson 5-cent coins struck in-collar
by the same wildly oscillating hammer die. In each case the hammer die
was well-centered when it first contacted the planchet.
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As it sank deeper into the planchet it shifted to the left side in
one example and the right side in the other. This movement left behind
a featureless crescent that separates the edge of the coin from the
edge of the field portion of the design. Transverse (crosswise)
striations found in this zone testify to the die’s destructive
movement. While this error resembles a horizontal misalignment, its
dynamic nature warrants a distinctive name.
I’d previously grouped such errors with design ablation errors, but
a more apt term would be a “skidding” or “sliding misalignment.”
Henceforth, “design ablation error” will refer to cases in which the
design is scraped off during a second strike.
In both 5-cent coins the hammer die shifted back in the opposite
direction after reaching the lowest point of its downstroke, smearing
the newly-struck design. This smearing is considered a form of machine
doubling called “slide doubling.”
Another effect of die skid can be seen on the obverse face of
double-struck 1976 Greetings token struck by the Israel Government Coins and Medals Corporation
(Israel’s mint). The first strike was centered but weak. As the hammer
die was lifting off the surface it shifted toward the southeast,
scraping the Hebrew letters generated during the first strike. The
hammer die descended again to deliver a second strike that was
horizontally misaligned a whopping 50 percent and strongly tilted. The
damage to the letters can be considered a partial design ablation error.
Die skid on the second strike can completely erase a newly-struck
design as seen in the quadruple-struck 2000-D Lincoln cent pictured, first discussed in
a column that appeared in the Sept. 13, 2010, issue. Here the reverse
die functioned as the hammer die. After a normal first strike, the
coin received a 73 percent off-center uniface strike at the northern
end of the reverse face, with the hammer die making direct contact
with the coin. After initial light contact, the hammer die shifted a
considerable distance northward, completely removing STATES OF AM and
E PLURIBUS UNUM. The final two strikes were
delivered in tandem (a saddle strike).