Verdigris

Sap and SS may be right ,, I did not notice the shine last night when I looked at the pic,,

If whatever it is has been on the coin for a substantial period of time ,, removing it will leave a different color where it was ,, if it is not actively damaging the coin ,it maybe best to leave it alone.

I would however segregate that coin from my other copper and Bronze coins just to be on the afe side of things.

Metalman

Does not look like bronze disease. I have battled the green death, and this does not look like it.
Based on my experience, here is what I would do:
1) I would probably leave it alone and monitor it as sap advised. This is probably the best advice.
2) If I just couldn't stop thinking about it and had to try something, I would start off as mild as possible. I would take a small fine, soft artists brush, dip it in distilled water and dab the spot carefully to see if the grey stuff will dissolve. Dab lightly with the brush at glancing angle rather than directly at the coin's surface to avoid any possibility of leaving marks. Then blot carefully with a soft paper napkin, pressing it against the spot. Work under a microscope if you have one. If the stuff starts to come off and and the coin looks better, then slowly repeat the process until you have the stuff removed. Go slowly, give the spots time to dissolve and make sure you are not making it look worse. If distilled water did nothing, I would try 70% isopropyl (rubbing) alcohol in the same procedure. If still nothing happens, the spots are pretty stable, I would leave it alone, it really does not detract that much.
I don't think olive oil will do the trick, but you could try that in the same procedure as well. Use the lightest oil at the store, which is usually the cheapest (do NOT use the heavy and expensive extra virgin types, they will not work as well).
Hope this helps!

t360, Why the lighter oils instead of the more pure ones, i.e. extra virgin types? I have always used the stuff I cook with which tends to be the better stuff.
Jim

I use light olive oil based on my experience cleaning several hundred ancient Greek and Roman bronze coins. I started out with the more expensive oils but switched to the lighter oils because I found they help remove dirt and encrustations better, probably because the smaller molecular weight hydrocarbon chains are better able to penetrate into the crud. Here in the Boston area, I buy Shaw's olive oil - light in texture - in a 1 pint bottle which lasts quite a while.

As a rule I never soak coins in oil or any other liquid, including distilled water. There is just too little control over the process, and even though oil is very mild, it does tend to darken the patina a bit if the coin is is left in it too long. Leaving a coin in water or oil for extended periods can help spread the bronze disease very quickly if it is present. Plus simple soaking does not work very fast or very well. So instead I pour out a very small amount of oil in a plastic cup and use a soft nylon brush to paint each side of the coin with the oil. Then after a few minutes I blot it with a soft paper napkin, pressing the napkin against the coin and very slightly and very gently rotating the coin (just a bit). Then I put the coin down and let it dry on a paper plate as I go on to the next one. The complete wet/dry cycle is really responsible for helping to loosen and remove the crud, not simple soaking. Of course this method keeps all the coins you are cleaning separate from each other and thus not able to spread the bronze disease from coin to coin. On ancients, between the oil cleanings I use tungsten and sliver pins (purchased from commonbronze.com) to gently pick off the crud that the oil helped to loosen. Then I iterate - paint with oil and blot again. You can alternate cycles between oil and isopropyl alchohol (hydrophobic solvent, polar solvent) for good results. This method also keeps your solvents clean and pristine (dirty solvents are not effective) and also uses very little solvent compared to soaking. It does use up paper napkins, but these are very cheap. Plus you can treat each coin individually from the start and not go too far and start to damage the patina on any one of them. For finishing up and bringing up the fine detail, I use the sliver brushes available from nemesis on vcoins and commonbronze. These are fairly expensive, but well worth it.

t360

did you ever look at an isopropanol soaked coin under 10 X magnification ?
The water in the isopropanol leaves calciumcarbonate stains from the water content
Since then it is pure acetone for me

MSDS does not sound to dangerous
You can drink acetone and it will not kill you
Nervous sytem depressant so is beer I think

Unfortunately it seems not wise to drink alcohol whilst acetoning your coins

http://www.bu.edu/es/labsafety/ESMS...Acetone.html

Last time I worked in a lab to calibrate an infrared computerised equipment to my needs , there were squirt bottles with acetone all around me for general purpose cleaning
First thing I learned in 1973 was to recognise the acetone peak on a gas liquid chromatograph ( Injection needle and body acetone cleaned but not fully air dried .)

The most dangerous is to put on gloves that are too short and plunge your hands in a bucket of solvent and have the stuff run into your glove with sweating hands . If you do not notice it the burn will be painfull . Happened to me with trichloroethylene .

I lost more skin of my hands by handling somewhat concentrated vinigar then with any other chemical product . Skin just peels off after a week or so .That is why I have an healthy respect of strong acids .