VOCABULARY TERM: SPALLING

Spalling. Minute chips of metal driven off the face of a die by stress during continued striking. Dies with a brittle surface are more likely to chip with small, thin flakes than those with a good tempering. Coins struck from such a die will either exhibit irregular raised areas, usually near the edge, or within detailed parts of the design where the die is weakest.

Working dies are subject to significant mechanical stress during constant striking. This amplifies minute discontinuities with metal crystal defects until the die cracks or deforms. The most common die defects not related to damage were spalling, cracking, chipping, and collapse. Cracks in dies are commonplace resulting from a combination of imperfect annealing and tempering of the steel plus excess mechanical stress on the weakest parts of a die.

Dies that were excessively brittle at the surface were more likely to spall than those with a good tempering. Chipping refers to thin flakes or millimeter-size pieces of the die surface that fall out of a working die. Coins struck from a chipped die will either have irregular raised areas, usually within detailed parts of the design where the die is weakest, or rough elliptical raised areas.

To read the complete entry on the Newman Numismatic Portal, see:
Spalling (https://nnp.wustl.edu/library/dictionarydetail/516782)

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