Most Hotpotters know that glass can breaks due to rapid, uneven temperature
change. Also known as thermal shock.
Why this happens may not be obvious.
When solid glass is heated or cooled unevenly, the part of the glass that is heated
will expand (or contract if cooled). The glass that isn’t changing temperature
stays the same size. This uneven expansion creates a lot of stress inside the
glass. If the stress is strong enough the glass will break. And that is called thermal shock.
A good example of this you can see in the picture.
Here I mixed glass
with different thickness and in combination with firing to fast it gave me an S
shaped crack.
The thinner glass got hotter faster than the thicker
glass and causes thermal shock.
I repeated the experiment with less heat over a
longer firing time up to 10-12 minutes and the results were much better.
The pieces came unbroken out of the HotPot, that was
already a big improvement.
When I came back to the studio the next morning
still some thermal shock had occurred during the night.
Overall I can say that with the lower heat and
longer firing time it is very good possible to fuse glass with different
thickness and from different suppliers together with a success rate of +80%.
