This piece is light like Schott glass. 12cm high x 12cm dia. It has a broken pontil mark and a fair amount of wear marks for such a light piece.
Very hard to photograph as it has virtually a mirrored finish. No sign that it ever had a stopper, but I can imagine it would look quite good with one. There is a slightly bronzed lustre - mostly evident on the base. This is not apparent on the glass on the pontil mark, which is pale amethyst, so I suspect it may be an applied finish.
I have included a photograph taken on top of the light box to show how thin and transparent it is against the light. It's quite an interesting effect......a perfect mirror when there's no light behind it, and a pale purple filter effect against the light.