When to hollow out?

[Buffalo Lips]

I have recently been working in clay sculpting heads, hollowing out, then firing. I want to do a figurative sculpture now but I don't know when to hollow and when not to. I can understand the torso but what about the legs and arms when they are only 1 to 2 inches thick? As well I would need to put a vent hole in for firing, How big and how do I plug it after wards?

Elmer

[fritchie]

It's been quite a while since I did anything in clay, but as I recollect a half-inch wall thickness is a general rule. That would say probably don't hollow for a one-inch piece, but do for larger. I would try for some low-visibility place to hollow and later refill before firing. You might need a tiny hole for venting during the fire, and of course a slow rate of heating and cooling is necessary.

[Buffalo Lips]

I read some where a person would put a drinking straw in the leg to keep a hole open to that area, is that do able to have a plastic straw in your piece while firing?

[The Forge]

It is not so much to hollow or not; but, how long will it take for the clay to thoroughly dry out. That is the reason for the 1/2" thickness. The general rule that I used when doing a firing was- if the sculpture is cold to the touch, it isn't dry yet.

[oddist]

I went with the straw idea but didn't like the idea of plastic.

I did an extensive web search and found PAPER straws.

http://www.aardvarkstraws.com/

Good luck.

[Buffalo Lips]

Originally Posted by oddist

I went with the straw idea but didn't like the idea of plastic.

I did an extensive web search and found PAPER straws.

http://www.aardvarkstraws.com/

Good luck.

So it's ok to let paper ie: straws burn up within your sculpture while firing?

[oddist]

Sure.

For instance, paper clay is a mixture of paper pulp and clay. http://www.nelsonmoore.com/art/Paper...ureHandout.PDF

The paper just burns out during firing.

[hbirch]

Originally Posted by The Forge

It is not so much to hollow or not; but, how long will it take for the clay to thoroughly dry out. That is the reason for the 1/2" thickness. The general rule that I used when doing a firing was- if the sculpture is cold to the touch, it isn't dry yet.

Some people have a "cheek test" where they check for coldness by pressing their cheek against it. In any event, dryness, not thickness, is absolutely the way to look at it. Hollowing figures is a fairly modern practice brought about by too many potters and not enough sculptors putting information out there. A figure can be fired of any thickness if done right.

I've done a decent amount of terracotta figures at 1/4 to 1/3rd life size, and rarely hollowed anything. I don't model cleanly either but bang things around lots and never worry about air bubbles. I've used both earthenware and raku bodies. Here's some of the works -- all bisque fired, mostly all completely solid: http://haneebirch.com/sculpture/life-sketches/ -- there's no harm in hollowing from underneath what you can if it gets big enough to not be tedious to do so. But I think hollowing generally limits the type of work you can do. Most of the people who have success with the slice-and-hollow method, for example, also have a vocab of very smooth surfaces. It's almost impossible to slice and reassemble a very textural sculpture.

Other advice above regarding paper and straw and such is very applicable for larger sculptures and can allow for very thick sections without shrinkage or unnecessary weight. Renaissance and pre-renaissance artists mixed all sorts of things into their clay bodies for working full size.

Like the above poster said, the key is just making sure things are dry. If there's no water in them and the person firing knows what they are doing, everything should be fine. I was lucky to know an experienced potter who had fired works for sculptors before and had no fear of shoving thick sculptures into his kiln, as he knew what he was doing. I let them dry anywhere from 1-3 months first.