Assorted mishaps can leave a coin with an island of die-struck design
marooned in the middle of an otherwise unstruck surface. The
downwardly tilted pole of a hammer die with a severe horizontal and
vertical misalignment will deliver its impact to a restricted area.
A die whose perimeter breaks away survives as a post that will
generate a centrally located design remnant. A broken die fragment,
trapped between a fully or partially intact die and a planchet will
generate an island of die-struck design, provided that the fragment’s
working face is directed toward the planchet. Finally, a
struck-through error combined with excessive minimum die clearance
will leave a depression on one face and an island of die-struck design
on the opposite face.
These possibilities raced through my mind as I first contemplated
images of the illustrated 2-rupee coin. The coin received two
off-center strikes, one of which was conventional and die-struck on
both faces, while the other was die-struck on only the obverse face
and surrounded by the unstruck portion of the planchet. On the reverse
face, an oblong depression lies opposite the island of die-struck
design. Although no definitive clues pertain to the die setup used,
coins carrying this design (2011 to present) are generally struck with
the obverse die serving as the hammer die.
My first impression of the odd-looking strike was that it probably
represented a struck-through error combined with an invisible strike.
In other words, an oblong object was struck into the reverse face
while, at the same time, minimum die clearance was greater than the
thickness of the planchet. Several examples of this error type are
known, including the Jefferson 5-cent coin whose images are reproduced
here. In this example, a small circular object trapped between obverse
die and planchet provided the only resistance to the impact of the
reverse die. This object apparently clung to the obverse die, as I
know of at least one other identical example.
Further study of the images of the 2-rupee coin quickly led me to an
alternative and unanticipated error combination. The shape of the
depression, and the portion of the obverse design represented (the
left pole), told me that the indentation was generated by another
The tips of the indentation are drawn out into thin creases that
resemble the corners of a smile. This shape is characteristic of
internal indents and internal partial brockages, an error type that
was covered in the Nov. 1, 2010, column and an example of which is
shown here on a 1999 Lincoln cent.
An internal indent occurs when a planchet or coin (“disc A”) is
struck off-center above or beneath a second planchet or coin (“disc
B”). The two discs lie roughly along the same axis and both protrude
from the striking chamber in the same direction, with disc B extending
farther out. When struck together, disc B leaves an indentation in
disc A that shows a characteristic bell-shaped outline whose flared
base extends out into the same thin creases.
The shape of the indentation results from uneven effective striking
pressure applied to disc B. The portion of the disc that is well
within the striking chamber is subjected to the greatest effective
striking pressure. This part of the disc is flattened and prolonged
into a tongue whose radius of curvature is smaller than the original
disc. This portion of the disc forms the dome of the bell. The portion
of the disc that lies close to the edge of the striking chamber is
subjected to lower effective striking pressure, so that the disc’s
original radius of curvature is maintained. This part of the disc
forms the flared base of the bell. The dome of the bell is also more
sharply defined and more deeply impressed than the flared base — again
due to differences in effective striking pressure. All these features
are seen in the indentation located on the reverse face of the 2-rupee coin.
During this strike, minimum die clearance was greater than the
thickness of a 2-rupee planchet. As a result, no trace of the design
exists beyond the boundaries of the indent and its complementary oval
of die-struck design. We have, in other words, a 50 percent off-center
strike with both an internal indent and an invisible strike.