Collectors of minting errors and die varieties frequently encounter
coins with one or more featureless lumps in the field or on the
design. Determining the nature and origin of such lumps isn’t always easy.
The two 1988-P Jefferson 5-cent coins selected for this week’s
column present such a diagnostic challenge. Each shows a large
swelling with a smooth surface at the top of Jefferson’s head. The
border of each swelling is fairly well-defined. The outlines of the
two elevations are similar, but not identical.
I initially thought that the two lumps represented two stages in
the growth of the same defect on the same die. One example shows
modest development of die flow lines consistent with a middle-to-late
die state. The second example has heavy radial flow lines consistent
with a very late die state.
However, a close comparison of the outlines of the two lumps
revealed differences that could not be reconciled with progressive
growth. Some fingers that extend out from the main body of the lump
grow smaller from the earlier to the later die state. The border is
also less clear in the later die state example. There are no common
die markers; instead distinctive die markers on each example show that
they were struck by different dies.
The lumps certainly weren’t interior die breaks. Although the
border of each elevation was fairly well-marked, they didn’t show the
clean, jagged lines of a die break.
They clearly weren’t die dents. It’s virtually unheard of for two
near-identical die dents to form on two different dies (the “extra
leaf” 2004-D Wisconsin quarter dollars are a notable exception). Die
dents this large are exceptionally rare, and finding two of this size
is highly improbable. Finally, we find emerging from each lump several
narrow fingers that merge with the waves of Jefferson’s wig. A die
dent would not coincide with or merge with the hair pattern.
The lumps are too large, too tall and the surfaces too smooth to
represent die erosion pits. The latter sometimes form in late die
states, leaving small “patches” or “blebs” on the coin’s surface. Die
erosion pits are very flat, with a rough surface and highly irregular
boundaries. They usually form in the field. They may be related to
loss of carbon (“decarbonization”) from the surface of the die face.
These lumps clearly do not represent trapped gas bubbles
(“occluded gas bubbles”). Such planchet defects tend to be quite small
and the distribution pattern will be different on every coin.
The one remaining possibility was a “die subsidence” or “sunken
die” error. Here portions of the die face deform and sink in as the
result of defective die steel or faulty die preparation. Sometimes the
design fades out or disappears completely in the affected area, an
effect readily apparent on our two 5-cent coins.
Perhaps the wrong type of steel was accidentally selected and
extruded into a rod from which the working dies were cut. Perhaps the
steel wasn’t forged properly, producing abnormal levels of carbon in
If the steel was of the proper type and was properly forged, then
a flaw could have arisen during any number of steps in die
preparation. Improper annealing, tempering and quenching can alter the
crystalline structure of the steel so that localized soft spots are
left just beneath the surface. These only become apparent after the
die has been placed into service.
Since two different dies from the same Mint and the same year
developed two nearly identical zones of collapse in the same area,
this would point to a problem more widespread than a single working
die. Perhaps the dies were cut from the same defective rod of die
steel, or were prepared by the same technician under the same faulty
conditions. Since the lump is well-developed in a die that doesn’t
show particularly heavy wear, it’s clear that this abnormality
represents something other than normal die deterioration.
Sunken die errors are highly variable in shape, size, relief and
location. While usually localized, the problem can affect the entire
die face. In many cases the margin of the sunken area develops cracks,
and some of the best examples straddle split dies.
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 email@example.com or to
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