How thick can clay be and still fire it, with out it exploding?

Question

I would like to make a human bust but I have heard that clay cannot be over about an inch thick when it is fired, otherwise it will explode! is that true.
if not how thick can it be? and how do sculptors like Philippe Faraut fire their pieces.

Answer 1

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I have fired a solid brick of clay 4" x 6" x 4". The secret is firing slow! Think physics and moist air expanding. Do a 48 hour heat up to cone temp, then a 24 hour heat down to cool. And let it sit for a whole day without opening. It is a four day firing rather than two days. I have never lost a piece in the kiln.

If you don't have control of the kiln, an inch is about it.

I would think Philippe Faraut has his own kiln and does a slow firing.

Answer 2

Yes, an inch is a pretty good guideline, though you can get away with more if you fire slow and not too hot. Most busts and other large pieces are hollow for this reason.

Answer 3

it depends on the clay you use. you can buy clay specifically designed for sculpture. though i don't know what you call it. you will need to speak to a specialist clay supplier. Though I do know someone who has used it to create large sculptures. although she cut the sculpture into blocks for firing. but that was only because she had a small kiln.

a technique you can use is to make an armature onto which the clay is added. this will make your bust hollow. if you use the right materials. the armature will burn away in the kiln.

the other way you could do it is make your bust. then make a plaster mould from that. the mould should be in two halves or even quarters.

with the mould placed together you can then slip cast the bust. you can make it as thick as you like, but nornally about 1/4 of an inch thick.

the beauty of that method is once you have your mould, you can make many casts.

Answer 4

learn something new everyday. i was told that the kiln exploded pieces because it had air in the clay.

Answer 5

Poke air holes into the bust, all over, making sure that it isn't layered a lot, which traps air. If it has air inside, it will explode, so you need to get every little bit of air out, or give it the chance to. Let it go in with a lot of tiny air holes all over, especially layers.