can you do another pic? can you hold it up to daylight and photograph it through one layer only (ie. not from the front of the vase, but from the top through only one side/layer of the glass with daylight showing through from behind, so the glass shows it's translucency).
That might, if it is clear, show the type of opaline it is.
If it is French you might see lots of little fine grainy bits in it - I can't explain what I see but it's different to that seen on Bohemian opaline glass of that period which seems to be to be very smooth when looked through with light coming through, no fine grainy bits. (btw please don't quote me on that, it's just my personal observation based on no ratified research

I'm a bit quizzical about the snapped off pontil mark. Is the foot trumpet shaped with the underneath indenting upwards towards where it was applied?
Or is the base flat with the snapped off pontil mark in the centre? it's very difficult to tell on your pic. I wouldn't have expected to see a snapped off pontil mark on a French piece but I have really seen very few in real life so that's not a very good indicator.
I also wouldn't have thought Italian or Bohemian - the glass and the style of the rim and the shape don't seem right for Italian somehow, the style/shape doesn't sit right with me for Bohemian (too slim and feminine looking although the rim shape and trailing does look right).
The rim of the foot is also fire polished is it?
Ivo, what about Belgian? what do you think?
I'm not arguing with you, but it's interesting about Baccarat - I wouldn't have thought Baccarat as a first thought just because, well, just because. Can't explain why - maybe the blue? I know you have seen many many many more pieces than I in real life though. Did Baccarat use this dark blue? Perhaps if French I would have thought St Louis first and then Clichy as the second consideration- again, just thoughts really.
m