I don't know how the heck it works, but from what I've heard acetone is very good at dissolving away most sorts of gunk without damaging the coin at all (then again, I've never tried it, I'm just recounting what others have said).
One of and maybe the most discussed subject here. If you check the Search Tab at the top and type in Acetone, might find a zillion (exageration) posts about that stuff.
I myself us a Brass wire wheel turning at about 1850 RPM's for cleaning coins. And if you hold it in your fingers, you get your finger nails cleaned too.
As usual, if you do not know how to properly clean a coin, just DON'T. And of course there is no real way to clean a coin so again, DON'T.