1862 Penny. Bronze Disease Or Green Patina?

The green patina is simply verdigris; a natural process with anything containing copper and exposed to air, damp, sea spray, etc. I wouldn't really call it a disease though.

http://en.wikipedia.org/wiki/Verdigris

However I wouldn't recommend cleaning it until you have advice from the experts here; it would probably be technically possible but may leave serious pitting to the surface once the green has gone.

It looks in good condition for it's age although I'm not quite sure how you would grade it?

Personally I'd leave it as it was; it's part of it's history for the last 150 years.

Mike.

On close inspection I think that this coin could have been buried in soil; maybe from nearly new, which would account for it's good condition and the verdigris. It seems to still have a little soil on it in places.
Maybe possible to soak this off and dry it thoroughly. The experts will know the best way to do this.
Certainly a nice item for the collection. :)