NNP

Cupping.  A malformed striking error in roughly cup shape. It occurs when two blanks, or a blank and a struck piece, inadvertently come between coining dies and are not ejected, one or both may wrap itself around the die forming a cup- shaped piece. Subsequent blows cause the metal to flow outward making the center extremely thin as the sides build up more around the die. Also known as capping.  Compare brockage.

Pressmen are ever alert to the sound of the presses under their control. The rhythm of the striking and the ejection or falling of the coined pieces into a hopper creates of series of sounds the experienced pressman is closely attuned to. He knows when everything is going well by sound more than anything else. When two blanks are fed into the coining chamber instead of one, the resulting strike of a brockage is a different sound.

Should the piece not eject but start cupping around the die this creates an entirely different sound. The pressman dives for the control panel to stop the press. Cupped pieces often wrap around die so tightly the have to be pried off the dies with considerable effort. The dies then have to be examined for damage. So cupping is a serious coining problem for any pressman.

In addition to the technical term capping, collectors call this error a "bottle cap" because of its resulting shape, or “snakeing” from its curling around the die.

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