Look at that Potomac for off gassing. Dull scales like that are signs of Cell Rot, probably rusted any near it. I would separate that one for sure.
Colored, Translucent, Faux Ivory and Cracked Ice scales are notorious for Cell Rot. Once saw a single razor in a glass case eat everything metal in an Antique Store case in 3 months.
I advised the shop owners, but no one did anything about it, 3 months later the case was trashed.