As @Oldhoopster explained, acetone isn't a 'dip' as that term is commonly used in numismatics. Acetone doesn't affect the metal* or toning; it only removes foreign matter that may have accumulated on the coin's surface. Actually it's not. An acetone rinse is arguably one of the most valuable conservation steps a coin collector can practice. When you buy a raw coin, you seldom know with certainty how the coin has been stored or what environmental contaminants it might have been exposed to. Circulated coins in particular may have accumulated organic matter around the devices, as well as other substances that might not even be visible — substances that can eventually damage and degrade the coin if not removed. * Except for aluminum coins.