Hi, Bill,
Your theory has a
good ground but, probably, cannot not
applied to this particular coin.
Indeed, many coins have a layered structure, well visible at the edge.
However, I would classify it as irregular. It looks like ``pate" for bisquits.
By the way, is there a commonly accepted explanation for this effect? It seems that a considerable mass
of the metal was forgered and flattened when producing flans in the same way as for pastry...
As you wrote in your page, usually, the surface of coins is reinforced by the shock and is much more
resistant to cristallisation, oxidation and other chemical and physical processes.
I show below a nice example of a small bronze with a very nice surface but
claylike substence in its interior (at least, near the damaged
part).
This is quite typical and understandable. I have a
fourree Voconius Vitellus which
resembles a small empty silver box: the core degraded and was dissolved.
On the other hand, the core of this
antoninianus seems to be crafted intentionally: it is very thin relatively to the overall
thickness of the coin and regular. Moreover, it is visible and intermediate level gluing the exterior thicker
layers of oxidated metal.