I think the fault / damage seen on this large Greta Vase is a burst bubble.
I'd like to confirm that and make pics permanently available for future reference at the Glass Queries Gallery
generously provided by Anne (Yobunny) http://glassgallery.yobunny.org.uk/thumbnails.php?album=37
Something Frank said in an earlier thread was in the back of my mind when I thought this but reading it again now I am unsure.
In topic Factory Faults
Bubbles near the surface easily crack and sometimes a hole to small to see even with a glass. Water has much better eyesight and has no trouble finding its way in where it evaporates when warmer with some of the vapour leaving the way the liquid got in. In doing so it leaves behind a deposit of the heavier minerals giving the whitish frosted appearance."
This bubble is entirely enclosed within the glass. No crack can be felt on the surface only a very very slight bump ...possibly. I guess there may be tiny cracks too small to see or even feel. The frosty area around the bubble seems to me more to do with internal shattering of the glass rather than mineral deposits. The frosy area is not a perfect circle around the bubble.
Frank also said
There is no way to tell if a crack in a bubble was caused during cooling, annealing or after the event.
I'm not sure exactly what it meant by this but if still refering to burst bubbles then I have the stongest feeling that this particular one was done after manufacture ....probably by me, by leaving the vase on a sunny window still, possibly after washing it.
The vase is destined for a place where it will be much appreaciated desipite this burst bubble which only shows from one side.