Occluded Oxides. These are small particles or clumps of oxide (often copper oxide or lead oxide) that occasionally are embedded in coinage ingots. If rolling brings the particles to the surface, the rolling mill operation can cut out part of the strip. Occasionally, particles will appear only after the coin or medal is struckThis medal, struck in a coining press, did not feed properly into coining position. It is a typical off center strike exhibiting part design, and part the original blank. Most items struck off center are struck in a coining press. Off center items stuck in a medal press would be extremely rare because it is examined at each manual placing into position for each strike.
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