How a coin’s design elements can be accidentally sunken instead of raised

Expanding die fill may explain incuse letters on a 2010 Pakistan 2-rupee coin
By , Special to Coin World
Published : 01/06/17
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Collectors' Clearinghouse column from the Jan. 16, 2017, issue of Coin World:

Numerous past columns have recounted the various ways in which normally oriented incuse design elements can appear on a coin. For the uninitiated, these are design elements that face the same way as the raised design, but are sunken. In most cases, these sunken design elements are out of position relative to their normal raised counterparts.

A brief review of known causes follows:

(1) Dropped filling (dropped letter, dropped number, and so on). Die fill (“grease”) accumulates and gets compacted within a die recess to form a cast. The hardened cast is eventually dislodged and ends up lying above or below a planchet. The dropped filling is struck into the planchet and then falls out, leaving behind an incuse impression. The impression will be normally oriented unless the dropped element flips over or winds up between the planchet and the opposite die.

(2) Struck through a thin, struck fragment. A thin piece of metal gets trapped between a die and a planchet, resulting in a uniface strike. The impact molds the metal to the recesses of the die. If the fragment is later dislodged and struck into another planchet, it will leave behind a set of incuse design elements. Once again, those elements will be normally oriented unless the fragment flips over before the strike or it winds up trapped between the planchet and the opposite die.

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(3) Struck through a shifted die cap or detached cap bottom. A late-stage die cap shifts out of position, or a cap bottom separates from its wall and moves laterally or rotates. The areas of the cap that had conformed to the recesses of the die face are slightly thicker than elsewhere. As a result, when these thicker areas are forced into a planchet by the impact of the die, they generate a duplicate set of normally oriented incuse design elements.

(4) Struck through a delaminat­ed coin layer. A thin layer of metal detaches from the surface of a struck coin. If the layer continues to face the die that produced its raised design, the layer will generate a set of normally oriented incuse design elements when it’s struck into a fresh planchet.

(5) Broken or chipped hub. When the raised details on the face of a working hub break off, the fracture plane is sometimes located just below the surrounding field. When such a chipped hub is pressed into a working die, and that working die is then struck into a planchet, the chipped component ends up slightly recessed relative to the surrounding field. Naturally, the incuse component occupies its normal position within the design.

(6) Die deterioration. Some forms of die wear can generate incomplete incuse elements (outlines, for the most part) that lie alongside their normal raised counterparts.

A different scenario

A few weeks ago I came across an extensive set of normally oriented incuse design elements that cannot be traced to any of the scenarios listed above. They are found on the obverse face of a 2010 Pakistan 2-rupee coin. A good portion of the Urdu script is incuse instead of raised, with these incuse letters occupying their normal positions relative to the flanking raised letters.

This is clearly not the result of a chipped hub. The edges of the incuse elements are too soft. Furthermore, a chipped hub is unlikely to involve a chain of unconnected letters and is equally unlikely to involve the complete loss of each letter.

I believe that these incuse letters represent the impressions of die fill that rose out of the letter recesses, above the level of the die’s field. This normally shouldn’t happen. When a die recess is completely filled, any additional “grease” will flow over onto the field, obscuring the edges of the design.

I suspect that in this case, the die fill expanded like warm dough rising out of a muffin pan. Dies can get rather hot during use, and it would appear that this material was prone to heat expansion.

One feature that supports this scenario appears at the right end of the arc of faint script. Here one character and part of another are actually raised. The die fill didn’t completely fill the corresponding recesses and instead generated a normal-looking “filled die” error.

As to what this novel type of “struck-through” error should be called, I suggest the term “bulging die filling.”

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