As far as "glitter/shiny/metallic" -
If it "sheds" or is scratchy - I would avoid using it. Especially for bedding or something that will touch a person's face.
I bought some t-shirts that had glitter on them. They are still scratchy many washes later. I also learned this "the hard way". I am also still finding glitter on some of the other garments that are in the same load.
Regarding the "metallics" - printed ink? - some of the "metallic" will wash off eventually - but it does not seem to flake or leave "dust"/residue" in my washer or dryer. I have been having a debate with myself about whether or not to use a "metallic" print in a face mask.