Several discussions here have mentioned that slabs for certified coins are not air-tight. I would assume that a copper cent that is certified as RD could change to RB or BN if not stored properly. Has anyone seen this happen? I have seen a few slabbed coins from (PCGS and NGC) that are certified as RD that either look brown or have blotches of brown color on a red background.
Yes, they can and have changed color in the slab. Remember, no slabs are airtight. FYI, the possibility of copper turning color is a large part of the reason why NGC has a limit on their color guarantee for copper, and, incidentally, why buying RB and RD copper from PCGS is in many ways a wiser choice than NGC (or ANACS/ICG/etc.)...Mike
I'm not a chemist, but as far as I know there is nothing that will prevent copper and silver from tarnishing over time, even in proper storage. Metals, with the exception of gold, oxidize, and not even an airtite container will prevent that. Guy~
Immersion in a liquid that doesn't dissolve oxygen would stop tarnishing. Not very feasible, but it would work, I believe.
Can the color of certified coins change ? You bet they can. I started noticing a little toning on a PR70 DCAM Silver Eagle, and that's when I put everything into Intercept Shield boxes. Seems fine.
