UV Blacklight

this is something I have never tried, but it would be simple to conduct a small test.

It would be interesting to see if any of the products that are out there to clean or conserve coins is detectable under UV.

I don't know the chemistry, but coins that have been cleaned will always have a residue on them. The stuff in this residue glows under UV light.

But I don't think it works with the "black" lights you buy at Walmart because they don't emit at the correct frequency. I think you can get small ones on ebay for about $20.

Most, naturally not all, individuals that clean coins with many different solutions, eventually rinse those coins in Acetone and/or distilled water for getting rid of such residues. If you read the lables on even most jewlery cleaners it stipulates that after such attempts to clean an object, you rinse with water. If not done, such solutions may tend to discolor the coins within a short period of time. Also, many of the solutions used to clean coins do not leave a tell tail residue that is detectable. Try it with Lemon or Lime Juices for instance. And although many dealer attempt ot enhance the appearance of some coins with a small abount of Olive Oils, those too do not emit any reactions with UV lighting.
And contrary to this some STUFF on coins as well as currency that are accumulated from people just touching may show up as a glow on a UV lighting system but have nothing to do with cleaning.

Thanks for doing that Carl. I didn't think it would make a difference. The best thing to do is look at a lot of coins and clean a few yourself to see what they look like. The retoned coins are the hardest to tell, but I can still spot it with good light. Experience and not gimmics work best.