It looks like "tarnish" rather than "gunk" or "dirt" to me - so I highly doubt any soaking in acetone is going to help. It could also be fire damage, in which case not even silver dip can save it.
These are the kinds of coins that dealers will routinely dip in silver dip (which is a mixture of thiourea and sulfuric acid). If they're dipping a whole bunch of coins in bulk, they don't really have anything to lose since they're not wasting a cupful of dip on a single coin; if the coin ends up looking market-acceptable to sell above BV after a dip, well and good for them - if it "looks cleaned" or the black stuff simply doesn't come off in dip, then back into the bullion bin it goes.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
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