Sue:
I agree with the many manufacturers but I don't think that's true about better quality pieces having the bubble sealed off. I've got some Krosno glasses with the same effect and the bubbles look the same.
The enclosed bubble goes back to the "Pippi" series by Orrefors before WW II, but I think the model for the pieces in this thread is Wirkkala vase 3586 for Iittala designed in 1959. I don't have one in my collection, but from the photos I've seen and my recollection of handling a couple I don't think the bubble is sealed off. You would get quite a different effect at the bottom otherwise. Also, the Wirkkala piece has straight sides. Fortunately, the Wirkkala pieces are invariably marked as such, helping poor punters like me who are less accomplished at identifying good quality glass.
The blue piece I show above has dead straight sides, like one Anne mentions, and the one shown by Rosieposie. The Aseda ones are tapered a little more than the original one in the thread.
One difference could be the thickness of the glass. My piece has relatively thin glass at the the top. The vase in Rosieposie's post looks to have slightly thicker glass at the top. I can't tell how thick the first piece in this thread is.
Everything about my piece tells me that the Ebeling and Reuss label is original and that it would be Swedish, given the time frame. I don't think all pieces are either Chines or Krosno, but I'm not sure in the absence of a label you can tell the difference.
I think we can say that Wirkkala is the designer for all these pieces, but a variety of companies have made them since. I'd prefer to own the Wirrkala original, but I still like my copy.
Just for fun I've attached a photo of one Krosno piece. The cutting may puzzle you; it was my uncle practising in his basement some time in his 70's.
David