Topic: another question about cracks

[josordoni]

I have this millefiori bottle - nicely made, but it has a crack running right round it from neck to neck via the base.  Thing is, the crack is totally internal, nothing can be felt on either the inside or the outside of the bottle.

here it is:
side view
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-6579
base
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-6578

This isn't the first thing I have had with this problem - I have an otherwise lovely Per Lutken Flame vase that has this fault in the front, and a Jobling Fir Cone bowl also with the same.

I reckon the bowl may well be impact, but even then I would expect some sort of bruising on the surface.

Or is it common to have faults like this that show nothing on the surface?  And is there an accepted cause for them?

[Frank]

Impact is possible but more likely the culprit was a stuck stopper and the hot water trick caused the crack at a stress point. Hot water and such thick glass with internal colours do not like hot water!

Try popping into a bowl of very hot water, it might complete the crack - then you can see how the piece was made 

[josordoni]

Ha! there's a nice trick for Bob's mum.... I could scare the wits out of the poor woman!

[Frank]

I meant put glass in the hot water, I don't think the other material would crack in the same way

[josordoni]

tsk tsk... I meant the glass too.

I thought I might ask her to wash it up, and then throw a hissy when it broke....

[josordoni]

and I wonder what would happen if I tried your trick of drilling holes in it....

[Frank]

It would deflate dramatically. But back to the glass... I doubt it would help much in this case, too far gone and the shape/size would make it near impossible to find the right spots.

[josordoni]

It's a shame though.  I am not sure about the stopper - it is not very tight fitting (obviously the right one, the base colour and canes match exactly) but I suppose it might have been tight before "they" heated it up ....

Not me though, Guv, not guilty.  You can't blame me for this one....

[Ivo]

To me it is still the result of improper annealing.  After releasing the internal tension in the glass by heating up/ reducing gradually in accordance with the recipe, the end product should be stable and able to cope with temperature differences within reasonable limits. A crack can form by impact - but is much more likely to occur due to temperature changes.  Ship a piece by airfreight and they will transfer it from a freezing airfield to a heated hall - * BLING*  Or buy it at some shivering market early in the morning, take it home and expose it to your comfort zone *BLING*. And of course everybody knows that you cannot drink hot tea from cold glasses, or turn a bottle into a hot water bottle.
The crackkkkkkkkkkk is a natural occurrence, and serves to make the glass rarer. You cannot hope to resell it as it will selfdestruct as soon as you do. Leave in the vitrine and enjoy on a day-to-day basis is the only remedy..