Thanks everyone for all the info & warnings!!
Good to know about the annealing crack - I did think it was odd that I couldn't feel the crack on the surface

Luckily, the jar has spent its life, to date, on a warm but not spot-lit shelf, so the crack hasn't grown!
To be perfectly honest, we're looking to sell the jar so that it can be fully appreciated by someone new ... any suggestions as to where is best to sell will be helpful. I see that there is quite a lot of Vasart glassware on ebay, but not sure if that's the best way to go?
BTW - what a great forum this is

Katie