I'm a coin collector and coins that have been cleaned lose a great deal of value. There has been a lot of discussion on coin forums about this and many say that acetone safely removes the green goop that results from silver coins being stored in PVC holders. It appears that this works, and most claim that there is no acetone residue left that can be detected on the coin. (The damage from PVC remains, however.)
I was wondering, is it really true that acetone completely evaporates leaving no residue?
I believe that some coin dealers clean coins to remove the normal 'dirt' that one would find on a circulated coin to make the coin appear less circulated. Some of us collectors prefer that coins be left as they are, except in those cases where the coin will be destroyed unless it is soaked in acetone.
So, is there any way to tell? And if there is, will the evidence be detectable for years to come, and if so, how? It's probably not a big deal to most collectors but I kind of like to know what I'm really getting.
Thank you for your kind consideration in this matter.
Thank you for your prompt reply.
I have been trying to find out on my own and I just couldn't find the information I needed, so I really appreciate an expert taking the time to answer my question.
J is correct. Technically, though, there may be an extremely tiny amount left on the surface - on the order of a monolayer of molecules physisorbed to the metal. … Even so, the normal layer of water that coats everything exposed to air would quickly displace the more weakly-bound acetone.
One may be able to tell by microscopy whether a coin had been cleaned with acetone. I imagine that the magnified surface of a coin would appear different whether it was dirty, dirty-then-cleaned, or naturally clean. I don't know exactly what that would look like because I've never investigated it. BUT, I suspect that one should look in very small pits and lines on the surface. If oils built up naturally from use, I'd expect them to have enough surface tension that they wouldn't penetrate the finest pits and grooves. But once solubilized with acetone, the surface tension would decrease, and they would penetrate, and would not be able to be wiped off because the wipe can't get into such tiny spaces. Thus, a coin that had been dirty then cleaned would probably have oils in the tiniest pits and grooves. One would have to be quantitative about what "tiny" means here, and I'm in no position to estimate that in this context. But I bet it could be done relatively easily if you used a microscope.
Good luck! - Josh
Thank you for your reply. I apologize for taking so long to say 'thank you' but I was ill for awhile. (Getting better!)
I do use a loupe to examine coins, as do most collectors. The companies that grade and guarantee coins use 10X magnification. I've been using 17X for most of my work and occasionally a USB microscope. Those are changing the coin collecting scene quite a bit because now just about everybody has the ability to see the coin's devices in extreme detail.
Cleaning coins is considered wrong but a bath in acetone is generally acceptable.
I can tell if a coin has had an acetone bath because there are no cleaning marks like you would see from silver polish, yet the coin is too clean for the amount of wear on the coin. Also, sometimes, the acetone frees the dirt from the devices except for the deepest crevices.
I had posted my question because another collector said it was impossible to tell if a coin had been dipped in acetone. I disagreed. So I was really hoping that acetone left a residue that would fluoresce or something. Oh well.....
I expect that tiny amounts of oils could be detected with proper magnification but then the question becomes: How do I know what that oil really is? So, again -- it's too bad that acetone doesn't glow in the dark. : )
If you could find an appropriate lab, a technique that would help you identify tiny amounts of oil on the surface would be mass spectrometry. Newish techniques like DESI and oldish techniques like MALDI would be able to ionize small amounts of material from the surface and analyze the mass of the molecules ejected. See
I haven't run either technique personally, but my impression is DESI is friendlier to a variety of different surfaces, and the samples can be placed in the source ionization stream under regular atmospheric conditions, making the analysis easier.
It's not the sort of thing that you'd up and do like you would with a USB microscope, though. These are expensive instruments, usually found in core facilities in research institutions, I think. It could be worth looking around at universities nearby, though. Most would run samples for you and charge by the hour, which enables you to not buy, run, and maintain equipment yourself. I used to run academic NMR facilities, and I know that anyone running an academic Mass Spectrometry facility would probably be open to discussing analysis of the materials on the coin surface.
Even so, the likelihood that you'd detect acetone is low, since it is so volatile. But you could try just in case some is bound up in the oils.