Long, long ago I had several dirty strands of faux pearls. When I washed them in dish soap and cool water, the coatings began flaking off revealing (mostly) opal white beads underneath.

In the 90s I bought some metallic coated Czech E beads that flaked the first time I wore them, on a necklace, in the shower. They were completely ruined. I returned the unopened packets to the bead store but they would not refund the wetted beads.

Lets see... also I reused a thrift store necklace with matte black beads... I knew it was glass... used it with some Venetian trade beads..... the coating eventually flaked to white.

I bought a rock tumbler, a small one. I did some experiments with tumbling shiny, colored Czech glass beads in grit (or sand) to create matte finishes. My main issue was the holes becoming clogged with sand and other particles.