If you had a coin that was valuable and had unwanted surface contaminants that a soak in Acetone would not resolve, it may be worth to send the coin into NCS or PCGS
Before sending them your hard earned cash, you may want to try what our own CCF member, who developed and sells
BadThad has posted before a list of solvents to try. His order is water, acetone, then xylene. Of course these are done one at a time and over a period of time with rinsing between.
If one of these solvents does not work, and you do not want to practice on non-valuable coins using things like MS70 and Ezest (Q-tip works for spots), the you could see if the slabbing companies could do it.
I also find if its just foreign matter on the surface, I can soak with one of the above and then use a microscope and porcupine needle (eBay - very inexpensive) to flake off the gunk that the solvent had worked on. The porcy needle is much finer than a toothpick and I have yet to scratch a coin with the needle itself. You have to be careful, like with a toothpick, you don't push around a piece of the gunk on the coin with the needle/toothpick though as that may scratch it depending on the gunk.