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Message:: [QUOTE="-jeffB, post: 5301650, member: 27832"]My bad, Doug -- I thought I'd highlighted the part of your quote about time not being a factor. (I've gone back and edited my post, so now it is highlighted.) That's the part that I haven't seen you mention before. The paper talks about an 18-hour soak in acetone, with light exposure, in conjunction with high humidity. The damage to copper surfaces was apparent at the end of that time. If I'm understanding your posts correctly (and I just spent some time going back through the first 20 or 30 of them), you're saying that you've seen coins discolor days or weeks after they were rinsed in acetone. I'm assuming "rinsed" means "not soaked for a long time". In that case, it seems like the paper has even less relevance to what you've observed. I'm feeling an increasing temptation to get a roll or two of fresh Zincolns, divide them up into experimental groups, and treat them various ways: 1) no treatment2) rinse with fresh acetone3) soak in fresh acetone, in light and humidity4) rinse with fresh acetone with a trace of acetic acid added deliberately5) soak in fresh acetone with a trace of acetic acid added deliberately Of course, since the color change "only happens sometimes", negative results from this test wouldn't prove anything. I'm not sure what test could; if the result depends on what's on the coin's surface, you'd need a set of coins with identical surfaces, and I don't know how to achieve that.[/QUOTE]