i know I am not supposed to clean coins but... I found this while coin roll hunting and it appears to be in great condition. The only problem is there is black gunk all over it. How do I get it off without damaging the coin? Or should I leave it alone?
That's a nice one for a roll find, but that "gunk" might be corrosion. Step 1: soak it in distilled water and see if any of the gunk dissolves. Step 2: let it dry. Step 3: if there's still gunk, soak it in acetone (from a hardware store, not nail polish remover). Many kinds of gunk that don't come off in water will come off in acetone. Don't rub the coin with anything, even a soft cloth. The cloth and the stuff stuck to the coin are likely to leave scratches if you do. Let us know what you find!
What he said. If it's softer then the acetone should work. If it's hard and crusty and the distilled water soak doesn't help, then it's probably corrosion and you're stuck with it
Leave as is and let someone buy it thinking they can fix it. Black may be good or bad but raised, green, lumps are active corrosion. The coin is ruined. Now if you want to practice on something, play around. You are going to need chemicals much different than anything posted here. That's because the ancient collectors know more about corroded bronze than all but a few in the U.S. forum. I recommend you post the coin over there to get better advice and some links to the methods professional conservators use for coins in this condition.
It's tough to tell from from the pic, but I see the little light green spot on the upper left wreath. It might be bronze disease. Overall though, I think the residue looks like organic gunk based on my view of the pic. It looks like it's an XF +/- so not worth much more than a Starbucks Latte. Try the acetone and see what happens. If it really is corroded under the gunk or has bronze disease, you're right, conservation becomes a more complicated chemistry project.
