I have been researching the cause of the halo, there are some really complicated things going on, I have yet to find a simple explanation to post on the board.
For those of you interested in the technical writings do a search for (indentation testing).
Basically you have a flow of metal away from the stamp site; some is directly away from the stamp (downward) and the rest flows upward and outward from the stamp. It is the flow upward that we see as a small bump but itâ??s the outward movement that accounts for the greater area. Much of this occurs on the surface. Here we see surface cracking, under a microscope this would appear as small folds of metal, this makes since as the additional metal must go somewhere. The surface treatment (bluing) will also be cracked as this uprising and folding takes place, this is what we see as a halo.
The candle and pencil tip is a great example; you see exactly what is happening.
Vern
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