Believe lead oxide is added to not only to help refract the light on cut glass, but also apparently to make the cutting easier - in the U.K. the percentage to qualify for full lead crystal used to be 33% I think, although some Continental factories drop this to 24%. If full lead crystal then the weight of a piece should seem heavy for its size - if soda glass then noticably lighter - try supporting the base section on three finger tips and then flicking. An increase in the lead content should give a slightly darker grey/slightly bluish tint. At 100%, it becomes opaque
Obviously with eight sides this shape has been produced in a mould, and if you look at the sides, and possibly the bottom, this fact should be apparent i.e. no grinding/polishing marks to be seen on the flat areas (if the opposite is true, then possibly the mould was leaving surface marks). The lips were ground/polished/bevelled to remove any irregularity after removal from the mould.
On the screen I'm seeing a colour which reminds me of Dartington 'Midnight' - rather than amethyst, is this just me? - I wonder if there is any sun-purpling.
Anyway, it's very attractive - although none of this helps you with an attribution, origin or date.