Let me just start by saying that I know that cleaning coins is a mortal sin and sends people straight to purgatory. But even so, if you look at this coin you can see that as it is, it has little if any value. Is there a way to remove the green and make it look halfway decent?
When a coin is being corroded like that, "cleaning" is the lesser of two evils at the least. There are a number of ways to remove the verdigris. Here's another interesting thread on the topic https://www.cointalk.com/threads/green-verdigris-on-coins.211198/
ask daveydempsey . I think he soaked verdigres (green) coins in olive oil for a week ? to get green stuff off coins. ask his opinion on your coin. @daveydempsey
here's his thread on verdigris cleaning. link: https://www.cointalk.com/threads/before-after-soak.244448/#post-1887501
just an update on my coin I was going to do...well I never got around to doing it. I might do it next week.
Verdi-care Ebay link: http://www.ebay.com/itm/VERDI-CARE-...022?pt=LH_DefaultDomain_0&hash=item4acde0e596
Olive Oil does work but it is not a few week process in the least, i have had a coin soaking in Olive Oil for the better part of three years. It has removed a lot of the green but it is a very slow way to go about it !! Basically you can replace the Olive oil once ever half year or year and just let it do its thing !!
Less threatening than solvents - smear the coin with ordinary Vaseline and set aside for a week. The first wipe should be nearly bright green. Repeat. Repeat, until the coin suits you. Vaseline removes NO metal, and does not polish; it's basically oil. Note that when you stop the process, the coin will likely show pitting. But the coin is pitted now. When you remove the corrosion, it merely becomes obvious.
One thing about olive oil - if you can figure out a way to SAFELY apply heat, it will speed up the process dramatically. Olive oil WILL vaporize and catch fire, as most gourmet cooks will tell you. I'm thinking if you have an outdoor grill, and no kids around, you could put the coin in a Pyrex container with a tiny bit of oil, and let it get very hot, then cool naturally, that "might" equal months' of regular soaking. Do not quench coins heated up in hot oil, as that causes microscopic pitting.
NOT A RECOMMENDED CLEANING METHOD: In the old days the old timers would burnish their copper coins with a brass brush... You aren't going to hurt it any by doing that...