100% Pure acetone nail polish remover after 5-6 years results....

@Early_Milled_Latin_America said:
Do they put that ingredient in all types of acetone? Is it OK for silver coins?

Apparently it depends on your jurisdiction. Some states (specifically: Arizona, California, Georgia, Illinois, Maine, Maryland, Massachusetts, New Jersey, New Mexico, Oregon, Tennessee, Utah, Vermont, Virginia, Washington, West Virginia, and Wisconsin) mandate that certain sweet-tasting toxic liquids sold to the public must contain denatonium. Obviously, a chemical manufacturer isn't going to really want to make two different kinds of acetone ("one for those states" and "one for everywhere else"), just in case they accidentally ship the wrong kind to Oregon, so they put denatonium in everybody's acetone, just in case. This would apply both to hardware-store-acetone and to nail-polish-remover-acetone. But if a chemical company only sells their products in places far away from those states and has no plans to expand there, they might not choose to add any denatonium.

I don't really know why they see the need to add denatonium to acetone to make it taste bad, since I reckon acetone tastes pretty awful just by itself; it certainly smells inedible. But I'm just a scientist who handles acetone in the lab quite a lot, not a lawmaker.

The main reason we usually say "for coins you should use pure acetone from a hardware store, not nail polish remover acetone" is that nail polish remover almost always has other stuff - besides denatonium - added to it, to make it smell prettier, which the hardware store acetone won't have. It's those essential oils that are likely to cause toning on a coin in the medium to long term, as they will almost always have sulfur in them. You got lucky with your choice of acetone, since it doesn't seem to have those fragrances present.

The concentration of denatonium is typically around 5 to 10 ppm, so we're talking 0.001% or so; rounding to the nearest 0.1% would certainly allow them to legally round up to "100% acetone" in the advertising blurb. There'll be more water present in your "100% acetone" (around 0.05%) than denatonium, since removing absolutely all of the water from acetone is both futile and hideously expensive. Denatonium is a solid at room temperature; when the acetone evaporates away, a tiny tiny amount of denatonium will remain on the coin. You won't see it, and it won't react in any way with the coin. I'm pretty sure not even the GC detectors ("sniffers") they use in the TPG labs to detect coin doctoring could detect denatonium in the tiny quantities we're talking about.

But the denatonium will still be there, and you would probably be able to taste it if you put one of those acetone-rinsed coins in your mouth. Denatonium was specifically designed to taste terrible, even at concentrations where it's barely present. I wouldn't recommend conducting such an experiment yourself, but if you were to take two identical normal coins, give one the denatonium-acetone treatment and keep the other one untreated, then put both of them in your mouth... the acetoned coin would definitely taste worse.