Here's an 1858 Flying Eagle Cent which appears to be large letters. This coin was so dirty and gummy you couldn't even tell it was a cent. It was the only coin in a box lot of tokens that I purchased last year. I soaked it for days in acetone, then rinsed throughly. I dried it for a day then repeated this process for a month. I think this is as good as it's going to get but at least I can tell what it is. Lol
It looks more than dry. I would soak that in some olive oil for a couple days. Might even loosen some of the crust. The over soaking in acetone will eventually dry the coin out and make it brittle. Usually the first soak I do on a dug coin is olive oil. It tends to soften/penetrate the environmental issues, so that they are easier to remove.