Proper Way To Remove Sticky Crud?

Here's a quick summary.

Got something you think is "goo" on your coin? Do this, in this order:
- Soak it in water. Rinse in fresh water. Let it dry. Is the goo gone yet? If not, proceed...
- Soak it in acetone. Rinse in fresh acetone. Let it dry. Is the goo gone yet? If not, proceed...
- Soak it in xylene or hexane. Rinse in fresh xylene or hexane. Let it dry. Is the goo gone yet? If not, then... too bad. It's not really "goo", it's actually corrosion. You'll need to switch to corrosion removers to clean your coin.

The ladder starts with water, because it's the most polar, and a surprising amount of real-world gooey things are highly polar and thus water-soluble. Sugars and starches, for example. Water is also cheapest and safest - no point in going straight to the expensive, hazardous solvents when water would work.

Now, if you know for certain that it's a specific kind of goo - PVC goo, for example - then you can jump straight to the solvent that works best for PVC goo (acetone), because you already know that water won't touch PVC goo. But for "unknown mystery goo", try the ladder.