Frederich, Tim on tue 10 oct 00
Hello,
Several recent posts have mentioned speed, cone number and soaking
of bisque firings. We feel that a slower firing in both bisque and glaze is
always preferable. This allows time for gases to escape from the clay body
as the ware is becoming vitrified or going through its structural changes.
Most glazes mature better at slower heating rates. There are exceptions to
this that may occur when working with special glazes. Slower firings also
allow for better distribution of heat throughout the firing chamber in most
cases.
The cone number that you bisque to will be determined by the clay
body that you are using, the way you apply your glaze and what works best
for you. There never seems to be any set of absolute rules when it comes to
working with clay. We can make suggestions but each individual needs to test
for their situation. In general a higher fired bisque will help burn out
more of the gases that might cause a problem in the glaze firing later.
Again this will depend on the clay body that you use and the materials that
make up that clay body.
As a general guideline most bisque firings do not require a soak at
the end of the firing if the speed of the firing was slow enough to begin
with. The gases in the clay have probably been expelled unless it is an
extremely "dirty" (lots of organic material present) clay body to begin
with. Testing will show if you have problems and then corrections can be
made. "Don't fix something that isn't broke or bad to begin with."
If you have questions about firing problems please contact me.
Best regards,
Tim Frederich, Orton Ceramic Foundation
Chris Schafale on tue 10 oct 00
This touches on a problem I've been wondering about. Experts say
it's better to bisque higher, to allow gases to escape fully. But I
find my glazes apply better when I bisque lower. Can soaking the
bisque at a lower cone substitute for firing higher? That is, if I fire
to an end result of cone 06, including a soak and/or slowed firing,
is that as good as firing to 04? Thanks for any clarification.
Chris
Light One Candle Pottery
Fuquay-Varina, North Carolina, USA
(south of Raleigh)
candle@intrex.net
http://www.lightonecandle.com
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