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kiln casting annealing
Posted: Mon Jul 21, 2014 9:00 am
by theanimallover
I did a brief class in casting and have a question...
If using just one sort of glass - one colour billet, is it still possible to have problems after firing? e.g the piece 'pinging' and breaking because of improper annealing? Or does this mainly happen when using incompatible glass.
Thanks.
Re: kiln casting annealing
Posted: Mon Jul 21, 2014 9:08 am
by Brad Walker
Annealing and incompatibility are two totally different kinds of problems. So even if you use a single glass so that incompatibility isn't an issue, you can still have problems with glass cracking and breaking due to improper annealing.
Re: kiln casting annealing
Posted: Mon Jul 21, 2014 11:24 am
by theanimallover
Thanks Brad.
Re: kiln casting annealing
Posted: Mon Jul 21, 2014 5:48 pm
by Morganica
Agree with Brad. If you hear pinging when you open the lid on a casting, it's most often thermal shock.
I anneal for the thickest part of the shortest dimension (which can be difficult to figure out with 3D stuff), and if the casting is more than about 3/4 inch thick I let it sit in the kiln for at least 12 hours before opening the lid. The plaster mold tends to insulate, so even if the plaster is at room temp, the glass inside can still be hot enough to thermal shock.