Thanks for that thought Ivo. I've had a look at Biot, but they're unmarked. I also feel certain that the bubbles are not pulegoso. Most of them are quite large and oval. In the sugar bowl the general alignment is round the circumference and in the jug from bottom to top, with more and more-ovoid ones toward the top. There's quite a lot of wear but not from use. I think the jug has been stood inside the bowl for a long while with regular sliding about for dusting.