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Displacement

Displacement.  The result of metal movement within a struck blank caused by the configuration of the die and the metal mass seeking to fill the nearest cavities of the die. The movement of the mass is called metal flow, displacement is the result of this plastic flow of solid material. There is some displacement throughout the blank (if it is one homogeneous mass, not clad) but it is obvious to observe as surface displacement, which forms the design, the modulated relief of the contours and cavities of the die.

Metal tends to flow towards the greatest die cavity during striking. The force of the blow causes nearby metal to flow into that cavity; it draws adjacent metal mass to replace the metal which flowed into the cavity. This movement of solid material, metal flow, redistributes the metal throughout the mass of the blank until all die cavities are filled (although this happens instantly).

The blank's mass is reshaped until it fits exactly the intended configuration of both dies (also expanding slightly to the limits of the collar). The design is formed, not by surface displacement alone, but metal flow occurs throughout the metal blank.

Obviously, displacement is best observed on the surface. However, we can view

the displacement within the struck piece if a coined piece is dissected and the change of internal grain structure is and the metal flow effect can be observed. Or, it can also observed by a lamination error where a layer of struck surface metal is severed from a coin. A minute amount of displacement can be observed within the exposed mass.

Interestingly, displacement does not occur beyond the first layer of clad metal. Numismatic writer Walter Breen named the line between two clad layers as the boundary. This is apt because displacement does not extend beyond the boundary of the first layer in clad coins.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor


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