My guess would be one coin had verdigris and you put all of the coins near it. Verdigris will spread. Get some Verdicare from Badthad, and after treatment if you do not have flips yet get any kind of envelope to put them in temporarily.
What kind of hell is this? I moved my collection onto a felt pad last night. Now I know for a fact this was perfect when I laid it down because I sat it down carefully on the felt due it being high-grade. Now today I got to put it in a flip, and NOW look at it!
felt is abrasive as well but thats weirld looking clean your vents or something its something in the aire you got a carbon monixide dector or any thing
If they have been sitting on a table for a couple weeks... did someone clean in the room and spray something? Maybe an air freshener of some type. Just some ideas.
If you look at coins in different light, at different angles, your going see things you didn't see before. That's the whole purpose of tilting and rotating a coin when grading it.
Sneeze, cough, drool, sweat, heck even tears from being upset while moving the coins to the felt pad musta come in contact with it. toning the thing black overnight. Bummer dude.
I'm sorry this has happend to your coins! Please consider the storage techniques Doug advocates - coins in a tupperware with a silica desiccant available for moisture control and coins inside a hard, inert, holder. I believe there's more such as limiting exposure to rapidly changing tempatures and light.
Two questions: 1) Why would you put your collection out on a felt pad? 2) Did you store anything else on the pad (or use it for anything else) before using it to lay out your coins? Felt tends to corroded brass instruments, so I assume it'd have a similar effect on copper based coins. And, yes, NiCu coins would still be copper based.
