Vintage Hubbell Glass Clip-On Earrings

These earrings have a beautiful turquoise clolour. They never where top quality but they have been kept in pretty good shape. All beads are present and without chips or cracks. The clip-on mechanism looks really old, possibly from the 50's or 60's, and seems to be made of brass. The earrings themselves are made of a silver looking material. There are marks on the back: 900 and the letters Y and B. I am not sure what that means but I am pretty certain that they are NOT silver. Could they be silver plated?

Well, in any case, I like them and I might wear them eventually.

Thanks for looking:)