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Message:: [QUOTE="-jeffB, post: 24660575, member: 27832"]When you come right down to it, "degreasing metal" is exactly what we're discussing here. <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie2" alt=";)" unselectable="on" unselectable="on" /> I'd say technical acetone is probably usually fine, but part of the "technical" grade is that there's not particularly close control on what kind of impurities appear in each batch -- just that there's not supposed to be enough of anything to interfere with "normal use". Getting grease off metal is "normal use", but being super-fussy about the metal's color after cleaning probably isn't. (I wonder if this is how acetone got a reputation for changing the color of copper coins -- all you'd need is a technical batch that's a little high in acetic acid, and presto, pinkish copper.) The part dismissing "Reagent/ACS Grade" in favor of "USP Grade" is essentially wrong. The Reagent grade is 99.5% pure, not 95% -- but the remaining impurities aren't guaranteed to be things that are safe for medical or food use. For USP grade, it is guaranteed to be safe, not for drinking, but for (say) preparing food containers, or extracting flavor components. USP grade acetone happens to have a higher guaranteed purity than reagent grade, although I'm not sure that's true in general for other chemicals. I'm pretty sure that the additional purity makes no difference for use cleaning coins.[/QUOTE]