Annealing range

The annealing range for glass is bounded by two temperatures. The lower and upper annealing points. Different glass has different temperatures for these points.

Between these two temperatures the glass is liquid enough for the molecules to move about and even out any stresses that may have built up in the glass while it was being worked. But not so hot that the glass can slump (which would occur above the softening point) and thereby ruin or distort any pieces in the kiln.

Generally speaking it is safe to anneal a piece anywhere within this range, but beware of annealing at a temperature that is towards the top of this range, as depending on the accuracy of your kiln controller you may find the temperature in parts of the kiln can unintentionally reach the glass' softening point.

It is always a good idea to check your kiln using a pyrometer or thermocouple to check the kiln's actual annealing temperature