How to Break Glass
Two things are simultaneously required for glass to break: a flaw and strain (in tension).
Glassblowers can create a flaw with a glass knife.
The tension (strain) may be created physically, by flexing the glass, or thermally, by applying heat. Typically, thermal strain is created by heating a glass rod in a torch and then touching the heated tip of the rod to the flaw on the glass tube.
This presentation provides an alternative approach, applying the flame to the glass tube itself to create failure. This technique is successful on tubing from 4mm to 65mm in diameter or greater. Although the cracks on larger size tubing may drift, this is still an excellent approach to obtain a more convenient shorter tube with which to work.
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