These were being sold as Barovier & Toso, which I dismissed when I bought them - I just thought they'd look good in a shade-less cascade pendant fitting I had (and they do!).
But when they arrived it was clear that they were very high quality, and indeed made in a technique that I can only find from 1930s-40s B&T.
Sandwiched between two layers of clear glass is a random distribution of very heavy gauge gold (-coloured) flakes that distorts the core layer to create a 'cellular' optic effect, with occasional large trapped bubbles stretching between them. The outer casing is quite smooth. They're about 15cm / 6" in diameter.
They call to mind pieces like these - but with none of the colour 'seepage' visible on a couple of them:
https://www.liveauctioneers.com/item/8558031https://www.liveauctioneers.com/item/17795000https://www.liveauctioneers.com/item/25914598https://www.liveauctioneers.com/item/25914600Unfortunately, a scouring of books and auction results has turned up nothing remotely similar in form or function.
Any pointers gratefully received, as always.