HA ! Very interesting! I took a very close look to my 2 Shrötter lense vases too and yes!
Both have these certain vertical lines going down, not the corner but the lens face and on the inside.
Although they go down a little randomly curved - not straight vertically, they don't look like "fractures" in my eyes...? (this is word I knew but still checked it in the dictionary it means something that is broken, right?) That is I don't think they are, but how would I know.
Still, I would guess it has to do with the process of making ?
Oops, and only now I read Christine already explained us about the annealing marks.
Anik ? are you sure, I hope your are wrong anyway, (sorry :kissy: ) and that your vase is not going to fall apart. There aren't any cracks going through the glass....?