Michael Daly wrote:
On 6-Feb-2006, Chris Jarshant wrote:

One more question. If I could heat up tempered glass slowly to a
ridiculous temperature, what would eventually happen? Would the
glass liquify, or shatter first?

It would anneal. Well, actually, it would reduce the stresses in the
tempered glass and would end up annealed if you then cooled it slowly.
If you just kept heating it, it would melt.

It will only shatter if it has a good reason. There has to be a reason for a
crack to form and/or propagate. If it already has a crack (or scratch) as a
stress riser _and_ the heating causes sufficient differential expansion that
the stress riser goes into tension, the crack will grow rapidly and the glass
will shatter. If the tempering process has created sufficiently high internal
stresses that heating one side causes the expansion (or even annealing) on
that side to result in serious tension stresses, it might crack as a result of
the high stresses without a precursor stress riser.

Personally, I take claims of tempered glass shattering "with no reason" with
the same enthusiasm as claims of people spontaneously combusting.

Mike

Didn't I write that I'm sure there is a "scientific reason" for it.

Hardly worth getting into in the grand scheme of things.