World Coins

Indian error coin prompts theories

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 2-rupee planchet.

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. 

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