Damage.. Not Rockwell test mark. Test is done on the Die to check the hardness. It would create a dimple on the die so when a blank planchet is struck it would appear as a raised area.
They might do a Rockwell hardness test on a die, but I can't see them doing it on the face of the die. They' d do it on the side of the body. Doing it on the face would tell them the hardness of the die, but then the die would be useless for striking coins. What good is knowing how hard the die is if you can't use it?
I understand that there are 2 tests. One on a Die and the other on Planchets. Here are quotes I want to share with you from the error-ref.com website - "A Rockwell test mark will appear on a die face as a small pit. On a coin it will appear as a tiny dome-shaped or cone-shaped elevation. It is most likely to appear in the field. No unambiguous examples of Rockwell test-marked dies are known among U.S. coins. This is not surprising as a Rockwell test mark is very hard to distinguish from a small circular die dent." And "When applied to a planchet, the Rockwell test mark will appear as a small circular pit with a smooth floor. Such planchets are supposed to be discarded. If a planchet with a Rockwell test mark is struck by coinage dies, the pit is not erased. The pit’s originally circular outline may, however, be distorted into a slight oval as the coin expands beneath the impact of the dies."
