Please Post Your Coins Which Have A Hemispherical Depression

These photos are too out of focus to determine the existence of a pressure ridge. A pressure ridge may only appear microscopely.

The test is before the strike. These indentions are too large to have been done by a Rockwell 15T test.

I am convinced that these marks on the 1977 Hong Kong 50 cents are damage, evidenced by pressure ridges around a portion of the circumferences. One diagnostic for damage is if there is a small (even microscopically small) pressure ridge of pushed up metal anywhere on or beside the feature.

If the feature was there before or during the strike, the strike would flatten that ridge.

A strike eliminates a pressure ridge because the striking pressure is enormous. For US coins, pressures used today are 35 tons for cents and dimes, 50 tons for nickels, 60 tons for quarters, 120 tons for half-dollars and 85 tons for dollar coins.

I now have some new information:

Rockwell Test Mark - Ability to survive a strike.

We know that the US Mint performs hardness tests on cent planchets as a part of its quality control. A key question pertains to the survivability of the resulting test mark through the striking process.

Ken Potter is currently striking medals to commemorate his 50th Anniversary of Serving Collectors. During the striking of one of the medals, a cent (First photo in the attached composite) which I had submitted for a Rockwell Test (Result 59.1 15T) was placed in the striking chamber on one of the planchets intended for the medal and struck with dies used to strike the medals.

The second photo shows the test mark after being struck. Results showed the diameter of the test mark was reduced somewhat by the strike and the internal conformation was significantly altered with the shape of the indentation becoming shallower and losing its smooth surface. I am also enclosing a composite of photos with sizes adjusted to bring dates and the test mark areas to approximately equal sizes for comparison.

The third photo shows the raised area from the test mark on the host after the strike.

, I would conclude that it is impossible to affirm the existence of a test mark on a coin, since the remnants of the mark likely will not exhibit consistent identifiable characteristics from one coin to the next.
My original research may be read here: https://conecaonline.org/rockwell-h...ncoln-cents/

Here's a mint set quarter with hundreds of circular and oval depressions. They're struck-through errors and they appear on both faces. More details in my next Collectors' Clearinghouse column.