Just noticed in this stored folder. Maybe the tape trapped in moisture?
Looks like they need removed and bathed in acetone. I always hated those folders when they wouldn't hold the coins.
Could be the tape residue reacted with the 10% copper content. Copper does like to turn green...... If you are going to take the tape off then try an acetone soak and see if that green will come off. It's worth a try.
"When they can't find anything wrong with you, they create it!"
The dimes will all need an acetone soak/bath and rinse. Acetone will remove the organics. However, since the tape does not cover the entire surface of the dimes, there will be a noticeable difference in tarnish where the tape is not covering the metal. Cheers, RickO
****"Now to the "is it necessary" questions: 1. Do you dip/soak all of your new acquisitions as a preventative measure, even if there is no sign of verdigris?" ****
No. To begin with acetone will have no effect on verdigris. So don't even bother using it for that, it's a waste of time. Acetone should only used on coins that need to have it used on them. In other words, on coins that have some sort of contaminant on them. Typical contaminants can be tape residue, any of various types of glue, shellac and varnishes, fresh fingerprints (and only fresh fingerprints because if it has been there more than a couple of days it's not coming off), oils and grease, and sometimes ordinary dirt and grime. Other than that, forget about it because acetone isn't going to work. But some folks will tell you that they use acetone on every coin, regardless. These folks are in the minority among all collectors. Most will only use it as needed.
Do you think that the green on my roosies is verdigris?
Isn't it just pvc? That would be my guess. Acetone works on tape residue and on pvc as well. I kinda like xylol myself. Must be used in a well ventilated room.