NNP

Mirror Image.  Matching opposite polarity; a reflected image. Struck pieces are a mirror image of their dies; dies are a mirror image of their hub or patrix. Positive and negative plaster casts are mirror images of each other. A mirror image is called contraposition. The congruent interface surfaces of two-part medals are often mirror images of each other.  Compare retrograde lettering.

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