That is in real good condition for sure, you can see plenty of details. It looks like verdigris has taken hold and put a coating over it. This is normally rough though?
The smooth texture may be because it was under pressure ie: in the ground so it was not able to grow outwards? Usually they get lumpy and only in sections, plus the fact it was probably watered ground or wet a lot of the time?
Certainly curious as to what has caused the finish, it would have been nice and shiny when lost.
I am soaking some coins in Olive Oil at the moment and it is removing verdigris well. Do not rub or try to clean with any abrasives.
Due to the condition it could be a pretty valuable find FYI.
Well done