Janet H Walker on sat 4 apr 98
...what is the best cone to use for a bisque firing?...
The answer really depends on details of what kind of clay you use,
what kind of glaze appliation you want to do, and other things.
There is really no need to bisque at all -- the clay doesn't need
it, the glaze doesn't need it -- but it is the conventional thing to
do nowadays.
Usually you choose the bisque temperature based on two things -- the
strength of the ware and the absorption. Strength goes up as the
clay gets fired longer but as the clay gets more fired it also gets
less absorbant. So you want the bisqued piece to be still absorbant
enough to take glaze easily and yet already strong enough to be
treated roughly (e.g. using glaze tongs) while putting on the glaze.
If you look at the various graphs of these two characteristics vs
temperature, you will find that for standard bodies, cone 04 is a
pretty good compromise.
Another issue to consider -- the "burn out" during bisque of organic
and other impurities and contaminants. Organics go between 700 and
900C, various sulphury things (found in e.g. earthenware clays like
RedArt) are still going around 1000C (cone 05). The reason for
burning these things out is so that they don't mess up your glaze
surface later on. If they are all gone during the bisque then you
can take your glaze firing up faster without running as much risk of
burps and blebs in your finished surfaces.
Look in Harry Fraser's book "Ceramic Faults and Their Remedies" for
much much more info on this issue. But if you just want to cut to
the chase, try cone 04 for bisque (even when you plan the final fire
for cone 06).
Jan Walker
Cambridge, MA USA
Talbott on sun 5 apr 98
We bisque our stoneware and porcelain greenware to ^06 using our
gas fired car kiln... anything hotter proves to be not as glaze absorbent
as we like... Marshall
http://www.PotteryInfo.com
101 CLAYART MUGS (Summer 1998)
2ND ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summer 1998)
E-MAIL ME FOR APPLICATIONS
Celia & Marshall Talbott, Pottery By Celia, Route 114, P O Box 4116,
Naples, Maine 04055-4116,(207)693-6100 voice and fax,(call first)
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