Hi all! I have this rather nice antoninianus of Herennia Etruscilla, but unfortunately the coin has some green and brown deposits one it. I know it's virtually impossible to clean these on bronze coins, but is it possible to get rid of them on a silver coin? I've tried picking with a dental tool, but the deposits are rock hard on the surface. Also, I know antoniniani aren't very high silver content, so is it possible to safely remove these deposits? Thanks!
You're right. The green deposits in particular are often rock hard. The most conservative approach would be to soak the coin for a day or two in distilled water. That might loosen some of the deposits, particularly the brown deposits, but also perhaps some of the green deposits as well. I would use a toothpick to see how much of the deposits can be easily dislodged. You could proceed to your dental tool, with great caution. I would suggest using the flat side with very light pressure. You don't want to scratch the coin. That might mitigate the deposit issue, though they will still be present after this process. At that point I would leave the coin alone. It will re-tone to a darker shade, so the deposits do not stand out as much as they do on bright, shiny surfaces.
Hi, I regularly restore ancient silver. Late antoniani are difficult. See here for a comparable cleaning project https://www.cointalk.com/threads/share-my-fun-describing-and-cleaning-a-small-roman-hoard.368534/
For what it's worth, I like it the way it is. It has a very attractive green patina overall, despite the deposits.
A combination of a stereo microscope review if to proceed then ultrasonic, H2O2, Freon TF derivative solvent mixture, EDTA (if necessary), camel brushing and the experience of John Lorenzo (Numismatist). P.S. I consider this easy since its silver alloy, copper or bronze substrates are the challenge. JPL
