Wow, nice => it looks a bit like it has been battered and then deep fried! ... ummmm yah I agree with Petersun => this is one time when you might as well try to clean the coin, because it's not worth anything if people don't even know what type of coin it is, right?
wow ... where do you start? (I'd wait until one or two of the Big-Shooters comes-up with a good game-plan) ... because I'll I got is => acetone and gently pick-off the big junk to see if there is anything underneath! (which is probably not what the experts are gonna suggest!?)
Hey, I did find this suggestion for cleaning verdigris from jewelry and coins:
Fill a container with enough vinegar to completely submerge the jewelry. Then place the piece into the container.
Allow the jewelry to sit for approximately 20 minutes, then remove the piece from the mixture. Use a cotton swab or a toothpick to remove loose pieces of verdigris form the jewelry. If there is still more verdigris that won't easily come off, return the jewelry to the mixture.
Rinse the jewelry with warm water and then dry it.
but again => you may want to wait until a more seasoned coin veteran chimes-in with a suggestion