Old strands of fake pearls are often actually glass, not plastic, and some of the ones I found at estate sales had the pearl-paint chipping off.  Acetone nailpolish remover will actually remove the paint coating completely from the pearl, revealing a milky glass bead beneath — which is actually quite pretty in its own right. I like them so much I put them on my multi-strand multi-pearl necklace, and now I put a lot of effort into finding old glass pearls.