7.6 Grease-filled dies
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Many twenty-cent pieces are known with weaknesses in the reverse lettering caused by die fatigue, poor metal flow, or insufficient striking pressure. Another cause of weakness occurs when the dies are improperly cleaned prior to use. If material remains on the dies before they are put into service, that material will interfere with how the metal flows into the die when coins are struck. A common obstruction is the substance used to clean and polish dies. Referred to as grease, this material can collect in the recesses of the die and if not removed, will prevent the design elements from being struck into the coin. The coin to the right is an example of a coin struck by an obverse die with enough retained grease that only a few of the stars were struck into the coin. |
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Grease-filled die obliterating stars |
