Yes, you have three things going on with this coin.
The
patina is a visible, yet extremely thin, layer of dark green oxidization which has formed over the surface of the "bronze" (actually a copper, tin, lead mixture for this late
Roman coin).
You also have some lumpy lighter green encrustations formed on the coin. These are a result of copper adhesions on the coin and/or copper welling up from inside the coin. In some cases these encrustations sit cleanly over the
patina, in other cases (as I suspect here) there is no clean
patina beneath.
Finally you have the bright spots where the
patina is missing. It is not only the
patina which is missing but
part of the surface of the coin has gone too so what remains is a
pitted missing mass. What is left is bare core metal slowly oxidizing.
There is nothing to be done to clean the coin further, but it should be stable and
still has the details necessary for
identification and enjoyment.
SC
