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solid greenware firing

updated thu 10 oct 02

 

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