Hi,
You bought a coin with a chipped
patina, you must have hopefully been happy with the coin and
price. I would say don't fix it, live with it, based on the reasons why you bought it. Fixing damaged
patina, particularly this damaged hard green
patina, would be wrong in my opinion. It is so different to the idea of cleaning a coin. Live with it would be my response.
Having said that I have a pierced
orichalcum sestertius. I plugged the hole with beeswax that matches the
patina colour, but it is temporary and totally reversable.
Regards,
Mauseus