Recently I removed a bead from what seems to be an old 1920s-30s necklace. I thought it was painted black, but instead it seems to be coated with silver that has blackened over the decades? The area that was under a bead cap is still metallic, as is the interior.

The bead seems to be blown glass, not plastic - one hole is much larger than the other.

Any clues as to why someone went to the effort to make a bead like this? A metallic, lightweight bead at a fraction of the cost of silver? What?

It measures 20mm.