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Re: underglaze firing

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From: Numo Jaeger & Michael Miller (jaegmil_at_TeacherArtExchange)
Date: Tue Jan 11 2005 - 21:00:10 PST

Occasionally there is some off-gassing which happens in the bisque firing
of greenware pieces that can cause problems on finished glazed pieces. The
off-gassing results in pinholes all over the surface of the finished work.
This is unsightly fault and sometimes very sharp. You can save money in
single firing work painted with underglazes on greenware but it's good to
know if the clay that you are using has a lot of carbonaceous materials in it.

Bisque firing at 04 instead of lower temperatures helps to reduce continued
off-gassing during a glaze firing.

I would insist that students wear an OSHA approved dust mask when mixing
clay raw clay materials because breathing these dusts are hazardous to your
health. Since many dust related diseases are cumulative diseases, it is
best to insist on safety precautions from the start.
-Numo 

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