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Mechanical Doubling

Mechanical Doubling.  Tiny lines or offset around the edge of lettering because of loose dies in the coining press. Also called double line by collectors, it shows a shift to one side forming a double outline of letters or numbers near the rim. The phenomenon is not in the die – it is not a doubled die – but is a chattering of a loose die during striking, particularly after a long press run. It has been described as a twisting of the die as it withdraws pulling small metal relief from its fixed position leaving large heavy relief, as a portrait or device, unaffected. It is cleared up by tightening the set bolts in the chucks holding the die in place. Such errors are usually not collected by numismatists because of their minor interest in the field.

A coin with mechanical doubling can be discerned from double die coins by the clarity of the letters or figures. True double die strikes (with a die that has two identical images) have distinctly formed letters, two distinct over-lapping complete letters. Mechanical doubling is a distortion of letters which look misshapen; the top of their letters or figures are smaller than their base, with a movement of the upper part of the letters or figures to one side.


NM19 {1991} Margolis, p 321-324.


excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


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