About Acetone baths

For me, the question is looking/grading a coin, can an expert tell it was soaked in acetone? Most likely not, but it was cleaned in the sense the very top surface was affected by a chemical.
I've heard/read that almost all coins were/have been, cleaned at some point in their life.

 

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Spots on coins after using acetone followed by a water rinse can arise for several reasons:

1) The acetone is not clean. You should only use fresh acetone from a newly opened container. Once used, discard that acetone and soak in another batch of fresh acetone. Discard that acetone. Some people like three soaks but two will usually perform adequately. DO NOT pour the used acetone back into the container of fresh acetone for the fresh acetone will then be irredeemably contaminated. This is a common source of spotting: When the contaminated acetone evaporates, it leaves behind whatever isn't acetone. And the contaminants don't only come from the coin but also the container you're soaking the coin in, your hands and/or gloves, and the atmosphere.

2) If you rinse the coin in water, use distilled water. You can buy it at the grocery store for little to nothing. I recommend distilled water rather than demineralized water because commercial distilled water has little to no mineral salts in it. Commercial demineralized is basically just the product of an ion exchange process that "soften" the water by converting the hardness (measured as calcium carbonate) into other products. Although "demineralized" water is also sometimes the product of a reverse osmosis process that also removes mineral salts. But in neither case is the product as pure as distilled water.

3) If you use a rinse water that contains anything but H2O, when that water evaporates it will leave the contaminants behind. That is the spotting you see on the coins. Now, some folks say if you dab the coin dry after rinsing with tap water or demineralized water, then you can avoid the spotting. I am not challenging that assertion. What I am saying is that for a coin of value, why would you take a chance to avoid the cost of a $2 gallon of distilled water from the grocery store?

4) Water has been described as "the universal solvent" and indeed it is. And in the form of distilled water, it possesses even more of that ability to dissolve what it comes into contact with. For highly reactive metals like copper, a rinse in distilled water must be a fleeting contact.

5) Finally, even after rinsing with distilled water, I agree with the advice to dab it dry as quickly as possible. As soon as the wet coin is exposed to the air, the water will start evaporating but not before it starts absorbing contaminants from the air, including dust and various aerosols. So, you want to remove the water before it can absorb contaminants which it would then leave behind even if dabbed dry later.

6) And, of course, you want to keep your reagent chemicals (acetone and distilled water) closed up as much as possible so that they don't absorb stuff from the air.

 

DesertGem beat me to it. My final rinse is a FLOWING rinse pouring fresh acetone over the coin while holding it to flush away any remaining trace contaminants or water. Then the pure acetone just evaporates away, usually in seconds, and leaves nothing behind.

 

can also burn a bit in the nether-regions. ouch

 

The key is the final rinse, sometimes a couple rinses. After all, if it took an acetone bath, it was because some contaminate on the surface. The acetone will loosen the contaminate but it doesn't magically disappear and the acetone is now also contaminated. Based on the contaminate, it may chemically change in the presence of acetone, but there is still a contaminate in the acetone. The final rinse should be with fresh, clean acetone that will quickly evaporate. MHO

 

No.

Acetone does not interact chemically with the surface of a coin.

 

@Southernman189, A CAVEAT TO WHAT I POSTED EARLIER IN THIS THREAD:

My experience is that acetone is reactive with aluminum coins. I learned this the hard way, destroying several aluminum French colonial coins in the process.

 

From all this I think I'd experiment with a "Common" average circulation quarter, Zincoln, nickel, and make mental notes to get the best results before I try a collectable coin.

 

I have never cleaned a french aluminum-bronze coin with acetone, but I can not see a chemical reason that a reaction would occur. If the coins were toned or had some corrosion, it would be understandable. I have a bag of foreign coins someplace that I accepted as a part trade, so I will look. Do you remember what colonies they were? Just academic curiosity. Jim