I came across a few of these in my collection of stuff.
They are Kodaloid printing masks:
Can anybody tell me what they are used for?
They are made of cellulose nitrate. I checked them. They are slightly shrunken but are otherwise good. No degradation. I'm not hip about keeping them. If they aren't valuable or readily useful for anything I'd just as soon get rid of them.
I'm a projectionist. I know how to handle nitrate. It doesn't bother me. Let's just frame the question this way: Would you store a Mason jar full of gasoline in your darkroom?