JAMES KALTEREN on wed 9 oct 02
i want to bisque some sculptures of solid (not hollow)greenware approx. 12x12x12".... sculpture clay body...electric kiln...any suggestions of rate of rise temp...max temp...etc...to keep them from exploding?...i will finish with a painted surface...maybe selective glaze areas...stains...
--- JAMES KALTEREN
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Snail Scott on wed 9 oct 02
At 12:11 AM 10/9/02 -0700, you wrote:=20
>>>>
i want to bisque some sculptures of solid (not hollow)greenware approx.
12x12x12".... sculpture clay body...electric kiln...any suggestions of
rate of rise temp...max temp...etc...to keep them from exploding?...i
will finish with a painted surface...maybe selective glaze
areas...stains...
<<<<<<<<
I suppose I should ask why they've got to be solid,=20
but I figure you've got a reason, and you can tell=20
us if you feel like it.
As for firing, I've fired stuff up to about 5" thick,=20
though not 12". I used VERY groggy clay (I think that=20
is the most important part), and candled VERY slowly=20
(more than a full day) BELOW 200=BAF, before coaxing the=20
temperature up to ^4 over the next two days. (A one-
shot firing - don't want to do that twice!) I didn't=20
hit red heat til about halfway.
Another way to make thick work survive with less (NOT=20
no) special treatment is to pierce it. Take a sharp=20
tool (I like a sharpened length of welding rod - nice=20
and stiff) and drive it almost all the way through the=20
leather-hard piece from the bottom or back. If in=20
doubt, go too far - you can always smooth over the=20
holes on the front/top side. I like them about 3/4"=20
apart... it works for me. Obviously, you aren't going=20
to be able to make the holes perfectly parallel, but=20
if there are enough of them, it'll be OK.=20
Basically, the moisture in the clay will no longer act=20
like the piece is 12" thick (6" =3D shortest distance=20
for steam to escape.) The moisture (steam) will think=20
that it's only as thick as the distance to the nearest=20
vent hole (more like 1/2"). This won't help with the=20
stresses of unequal heating, (dry greenware has a=20
rotten thermal conuctivity) so you'll still have to=20
fire mighty slow, but it will prevent nasty explosions,=20
and that's what would really bite the most!
-Snail
Reno, NV
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