To Rinse Or Not To Rinse...that Is The Question?

@Andrew99, there's lots of controversy here. I work in an analytical laboratory too and often clean ion sources for mass spectrometers. As you know, even analytical grade acetone can leave a trace residue that causes molecular contamination and makes an ion source useless. The contamination levels are miniscule and invisible to the unaided eye. The numismatic community seems okay with what they can't see, and nobody to my knowledge has reported any long term effects from acetone usage, but there probably hasn't been a valid study either. If the acetone is technical grade or has become tainted (easy because it's such a good solvent and leaches out plasticizers and other compounds from containers) it's that much worse, so I recommended the evaporated-drop-on-a-mirror test since it's better than nothing. Personally I use acetone on selected coins to efficiently get rid of gunk and "people goo" but the final quick rinse is ethanol to get rid of the acetone, and pure ethanol leaves no residue. Many folks shy away from water even when distilled for a variety of reasons. For me I wouldn't use it as a final rinse because it dissolves CO2 from the air and becomes acidic... water exposure on a coin during the rather slow evaporation process can thereby lead to corrosion.

Not a bad idea to do the SEM imaging to get an idea of residues remaining after rinse methods. This thread has really got me thinking, since the commonly accepted wisdom around here has been always to soak in acetone, then rinse in clean acetone allowing to air-dry. The underlying assumption that the acetone is pure could be quite faulty depending upon the source of the acetone.

I'd love to try this test but would have to pay by the hour to use the SEM so wouldn't be worth it. I would want to be thorough in testing different brands of available acetone and comparing to DCM, DI H2O, or Xylene rinse. Probably wouldn't spend time with alcohols since people normally go for the extremes in polarity and don't spend too much time in the middle. One person here who might have already done similar studies is BadThad, I recall he did extensive research in developing Verdicare and probably looked into the rinsing issue.

I pay nothing for SEM time, but how to design study? Buy different grades of acetone? Probably we'd see not much even on imaging, but the EDXA will pick up residual carbon on the surfaces.

I would probably source commercially available acetone from retail establishments accessible to hobbyists, since this is where coins collectors would get their's. And also throw in drug store nail polish remover too; we always say not to use it around here but it's worthwhile to try it too just to see.

I was thinking, the surface roughness of a coin in the SEM would likely be so high that you might have a tough time seeing exactly what is residue and what is topography of the metal surface. Of course you might see charging artifacts coming from the grime that would provide the contrast you want, but a better way to test the rinsing solvents would be on a very smooth surface (I would go with a doped Si wafer for this) and let the drop evaporate on the surface.

I think EDX is a great idea, but on second thought it might not work; to get a nice clean signal you would have to have a longer integration time and the electron beam beating down on the sample would likely vaporize most of the organic residue. You can see this happening on metal surfaces with fingerprint oil in live view as the beam scans, the droplets just shrink and disappear.

Mass spec sounds like a decent idea; I'm not as familiar with the required solvents for it though.

I would never touch any towel, clean or otherwise, to a coin of any value.

By the way, this has all been discussed several times before...

https://goccf.com/t/98298
https://goccf.com/t/132833
https://goccf.com/t/241856
https://goccf.com/t/249688

I think perhaps the mass spec would be better used to measure the acetone itself instead of worrying about rinsing off a coin's surface. You could concentrate any impurities by allowing an open container of the acetone to evaporate for a little bit, and run it straight through; I think acetone should be usable by itself.

Depending on the source of the acetone/rinsing agent you could also contact them for a COA that should tell you the same thing.

Either way I think the most useful wisdom from the threads jbuck linked is to do a spot test with your acetone before using it; pour some into a spotlessly clean glass container and let it evaporate. If you see any residue, then beware. Will that residue harm your coins if you use it anyways?

I agree with jbuck and bio. NEVER rinse with water after acetone as it will re-hydrate the surfaces. Ultimately, water is the enemy of coins as it leads to corrosion. After soaking in acetone, rinse the coin with clean, fresh acetone and put it into storage. No drying period is needed since acetone evaporates from a metal surface in seconds, leaving a nice dehydrated surface.

Personally, since I'm a chemist, I have access to reagent grade acetone. It's the only type I use. From my research, most consumer grade acetone is actually very good, usually >99% pure. You guys are getting over-the-top with concerns over residuals that may be present. Most of the impurities in a quality acetone are volatile enough to evaporate on their own.

Using SEM-EDXRF after an acetone rinse to detect "impurities" would be an exercise in futility. I work with an SEM-EDXRF almost daily.

Pretty cool, today I'm meeting with Hitachi to go over a quote on this new instrument:

http://www.hitachi-hightech.com/eu/...pn=em-su3500

I'll be getting a new toy in my lab very soon!