This is one of my rarer varieties (R5+, one of the tougher ones at that) which appears to have been lacquered at some time in the distant past. there is also some unusual coloring. While I generally avoid doing anything with my copper, does this look like something which can actually be helped by conservation?
The lacquer could be removed but it would be a touchy process. I would use acetone. I would recommend a quick soak at first to see just how quickly the acetone is going to effect the lacquer. Sometimes acetone doesn't take long at all... other times it takes hours. Then after the lacquer is gone you have to watch for the surfaces to corrode after being covered with lacquer.
I would think the best place to start with anything along the lacquer/glue/plastic line would be acetone. Would you leave it alone?
If it's a high value coin, conservation is always best left to NCS. If not, I would attempt it myself. Always start at the high end of the polarity ladder and work down: 1) distilled water 2) acetone 3) xylene No matter what, the verdigris needs to be addressed. At minimum, I would dehydrate it with acetone and immediately put it into an airtite holder to slow the corrosion process.
Whatever else it is on the coin, acetone is not going to get the verdigris off. Couple that with the rarity of the coin and it turns it into one that I would not mess with myself. I'd send it to NCS.
