Monday, 11 May 2009

Devitrification Temperature Range

Devitrification is the beginning of crystallisation of the surface of the glass. It can look like a dirty film over the whole piece or dirty patches. At its worst, the corners begin to turn up and become “wrinkly”.
This piece shows both mild devitrification and more severe wrinkling on the right side.

This occurs in the range 700° – 760°C. This means that you need to cool the project quickly as possible from the working (or top) temperature to the annealing point. There is evidence to show that dwelling for a long time in this range on the way up to top temperature can promote devitrification too.

The lower graph line shows the  temperature relationships between annealing (glass transition), devitrification and blowing temperatures.