Bernard - many thanks for reproducing these past notes on bubbled material. I do have one or two pieces of known Pompeian, but my deeper blue vase in this thread (unlike the blue of my grapefruit dish wich is marked) is still giving me some doubts. It is without any depression where the pontil would have been detached, although it seems to have the remnants of of the pontil outline, plus much wear.
I have another purple bowl which may also be Pompeian, although I'm not sure.
Bearing in mind your earlier comments............."If you can't find a mark, it is probably best to take it to a glass fair and ask for an opinion. I doubt whether you will find anyone prepared to attribute it over the Internet"
- you might care to take a look at both for me in September, at Cambridge - that is if you are going.