If
a project has not been sufficiently annealed, it is possible to
re-fire to do a good anneal.
You
need to establish a slow rate of advance; one that is much slower
than for the heat up of a fully annealed piece of the same thickness.
This is because you can heat shock the glass much more easily than
one which is adequately annealed. I suggest going at about half the
rate of a normal firing for a piece of the same thickness.
You
have to make sure all the glass is above the annealing temperature so
it is advisable to go up to near the slumping or softening point of
the glass to ensure all the stresses are removed before beginning the
annealing process. If you want or need to retain the level of
texture of the previous firing, you will need to go to about 20ÂșC
above the annealing soak point of the glass and soak there for at
least as long as you plan to soak at the anneal point.
Anneal
at a rate (after the anneal soak) that is considerably slower than
previously used. Look at the Bullseye annealing schedules for thick
glass, or their project notes for annealing bowls to get some good
guidance on the rates of cooling.
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