Dull Coins After Acetone Bath

In my opinion the original looks much better than the "cleaned" version. It now looks just like a cleaned coin.
I would not have used acetone on it.

A trick that some people would do when selling copper with some minor residue on it is rub a small amount of olive oil on the coins. This soaks into the residue and makes it dark while making the surfaces glossy. Of course an acetone bath removes the oil and then the residue stands out.

Acetone never discolours bronze coins under normal use (if you're soaking coins for 18 hours, and letting the acetone all evaporate away, then sorry, but you're doing it wrong). What acetone can do, however, is reveal damage that has been done in the past and has attempted to be hidden, as Andrew99 suggests. If the coin now "looks cleaned", then I suspect it actually was cleaned by a previous owner, perhaps treated using oil, verdi-care, or something similar. The acetone has removed the cleaning agent, showing the true nature of the coin.

The nature of the grey deposit cannot be determined by the pic, but it is one of two possibilities: "dirt" (which should eventually come off with distilled water and acetone rinses) or "corrosion" (which isn't going to come off without harsh chemicals that will destroy the coin). If the coin has actually been previously cleaned, then I'm afraid the likeliest answer is "corrosion" - whoever did the cleaning tried to remove the corrosion from the coin, but whatever they used to clean it didn't get down into these recessed areas of the coin.

I have examples of Canadian small cent George VI specimen strikes, in PCGS holders (no less) and within 5 seconds of looking at the coin, I knew it was acetone soaked. Specimen strikes are different animals though, the surfaces of those fields are like mirrors (equivalent to early US proof strikes of 1-cent coins)... the effect on the mirror fields leaves a "gasoline on water" appearance to the coin's mirror surfaces, and halos around the devices.

I have a few examples in my collection, including a 1950 specimen strike that became a "sacrificial lamb". I'll try to remember and post a few photos later this week.

^ If they detect it, they will return it as non-gradable, as it could deteriorate further in the slab. I got taken this way once 20 years ago with a nice, glossy large cent that a quick acetone dip revealed hidden green in the recesses.

Of course. I'll post an update later this week.

Well, I couldn't really get rid of the dullness but it became much less visible after a few additional baths which is good. It's not perfect but it means the hunt for te perfect example is still on :)

Thanks for the wonderfull insights and tips.

Really love this community!