Oil, grease, dirt and other contaminants that
coat a die or clog its recesses have a well-known potential for
generating accessory design elements on the surface of a coin.
Dropped fillings of compacted die fill will
leave behind incuse traces of whatever design elements they once
occupied in the die face (Collectors’ Clearinghouse, April 19 and Aug.
16, 2010; Oct. 29, 2012). A thin film of oil or grime can produce a
range of surface film effects, including surface film doubling,
surface film afterimages, and surface film transfer (Collector’s
Clearinghouse, Sept. 1, 2008, and May 2, 2011). I’ve even seen one
case in which a thick patch of die fill attached to one die was struck
by the opposite die during a clash. When it struck the next planchet,
it left a brockage behind. In other words, the incuse, mirror-image
design elements on the surface of the coin were generated by struck
die fill, rather than a piece of struck metal.
All of these extra elements are either incuse
or lie at the same level as the field or design. But it now appears
that die fill or “grease” has one more trick up its sleeve — the
production of accessory raised design elements.
The phenomenon has so far been observed only
in 1995 Lincoln cents and involves only the last digit of the date. In
some of these “grease-struck” cents we see the emergence of a second
raised 5 lateral to the normal digit. Like a scene from Invasion of
the Body Snatchers, the replicant grows alongside the original and
eventually replaces it.
For reference purposes, the first photo shows
a normal date, and the second, a 1995 cent struck through “grease.”
For reasons we don’t understand, as with most copper-plated zinc cents
the substance was smooth and imparted no texture of its own to the
coin. Instead it helped preserve the original streaky surface of the
Our third example shows the appearance of the
false digit to the right of its normal counterpart. The upper bar and
lower curve of the secondary digit are larger than the normal version
and rotated slightly clockwise.
A similar state of development characterizes
our fourth piece; here the tail of the secondary digit lies alongside
the faint tail of the primary digit.
In the fifth and last cent, the original digit
is no longer visible and the secondary digit has taken its place.
At least two die pairs are represented among
the three pieces with secondary digits.
While the appearance of these secondary
numerals is clearly tied to the presence of some kind of die fill, the
mechanism is obscure. I suspect that the substance has the consistency
of a very stiff gel that is firm enough to hold an incuse image of the
numeral 5 and then transfer that image to a planchet. I further
suspect that the entire process begins as the substance conforms to
the recesses of the obverse die, forming a lining for that cavity.
The biggest mystery is how that lining
migrates from the die’s recess and onto the adjacent field. There’s no
line of separation between the extra 5 and the rest of the
struck-through surface. It may be that, during the strike, the gel
stores a lot of potential energy while under compression. When the
hammer die retracts, the potential energy is released through
expansion of the gel in all directions. Radial expansion of the die’s
coating may push the lining of the die recess out of its cavity.
However it occurs, once the stiff lining has moved onto the field, it
is struck into the planchet, leaving behind a digit of very low
relief. The impact of the strike presumably flattens the mold so that
the impression it leaves on the coin is slightly enlarged.