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naomi d.

Interior Supports?

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I have begun, again, a sculpture - a hollow figure which will ultimately be 3 1/2 feet tall, a standing woman. I'm using 1/2" slabs. I have the torso, and due to kiln height constraints, planned to cut it into two pieces. Today, due to weight causing the bottom to split and crack, I went ahead and cut it into the two pieces, which are currently resting on foam. I still need to add legs, head and arms. I'm thinking I do need to add some internal supports, but then I've seen pieces without any. These are usually columnar. I'm concerned not only due to the weight of the remaining parts, but also sagging in the kiln. How much do I need to add? Just half circles, or braces from one side to another? My largest piece before was a bit over a foot, though she sagged on her poor bony legs, despite the "quilt" she was holding. I do plan to fire the leg section upside down. Anybody had to deal with this, and did so successfully? I am grateful for any advice and suggestions.

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I have begun, again, a sculpture - a hollow figure which will ultimately be 3 1/2 feet tall, a standing woman. I'm using 1/2" slabs. I have the torso, and due to kiln height constraints, planned to cut it into two pieces. Today, due to weight causing the bottom to split and crack, I went ahead and cut it into the two pieces, which are currently resting on foam. I still need to add legs, head and arms. I'm thinking I do need to add some internal supports, but then I've seen pieces without any. These are usually columnar. I'm concerned not only due to the weight of the remaining parts, but also sagging in the kiln. How much do I need to add? Just half circles, or braces from one side to another? My largest piece before was a bit over a foot, though she sagged on her poor bony legs, despite the "quilt" she was holding. I do plan to fire the leg section upside down. Anybody had to deal with this, and did so successfully? I am grateful for any advice and suggestions.

 

 

Hello Naomi,

 

I understand your concerns.

 

What cone are you planning to fire your piece to? For the work that I do (almost all sculptural), cone 5 works nicely. My taller pieces shrink more at Cone 10 and are subjected to more unnecessary stress in the firing. So if you can do Cone 5 or even lower, that's one option to get less slumping.

 

I assume you are using a traditional clay body. Your 1/2 " slabs are pretty substantial. I don't know if additional internal supports will help since this will increase the weight even more. However, if you are planning to incorporate internal struts, I would recommend a hollow tube form. Think of it as a hollow pipe and using this as an internal armature.

 

Have you thought of using paper clay for your tall pieces?

 

Hope this helps

Anthony

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I think you could use interior structural support in the torso using concentric circles 1-2" deep around the interior of the torso. Not really concentric but following the shape of the interior.

Cones and cylinders are strong forms. Could it be possible you were building before the lower parts were set up enough to withstand the weight? Sometimes if you add too much too quickly, the wet clay can't take it but stiffer clay could.

 

I agree with Anthony that paper clay or a clay with nylon fibers may be a benefit for what you are trying to do. Meanwhile you can patch the crack with a paperclay patch. Let is set up. Try a heat gun on the lower part to speed up the process and keep a wet rag on the edge you need to add to.

 

Marcia

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I have begun, again, a sculpture - a hollow figure which will ultimately be 3 1/2 feet tall, a standing woman. I'm using 1/2" slabs. I have the torso, and due to kiln height constraints, planned to cut it into two pieces. Today, due to weight causing the bottom to split and crack, I went ahead and cut it into the two pieces, which are currently resting on foam. I still need to add legs, head and arms. I'm thinking I do need to add some internal supports, but then I've seen pieces without any. These are usually columnar. I'm concerned not only due to the weight of the remaining parts, but also sagging in the kiln. How much do I need to add? Just half circles, or braces from one side to another? My largest piece before was a bit over a foot, though she sagged on her poor bony legs, despite the "quilt" she was holding. I do plan to fire the leg section upside down. Anybody had to deal with this, and did so successfully? I am grateful for any advice and suggestions.

 

 

I have used two methods: (1) for a 46" tall figure .... I made a beanbag form in the rough shape of my standing figure and suspended it from a beam in my studio. The figure was worked in 1.5" coils around it and the beanbag armature worked a treat. As the clay dried, the beans could expand into the area left at the top and when the whole thing was stiff enough to self-support, I opened the top of the beanbag and extracted the beans with a vacuum cleaner - it filled the cleaner a few times! I then completed and closed the sculpture. I too had to cut the figure in half for firing - I used fine piano wire, held very taut by me and a friend whilst another friend supported the work. On the whole it worked very well, but I would advise trying to find a "natural" join, as I can still see the join in my sculpture - friends tell me I'm picky!

(2) for a 3ft tall crouching figure .... again using 1.5" coils, I built two intersecting internal walls whilst building the form and this worked very well, but I had the inside space to do it. I've also used rolled up cardboard strips (the sort with one wavy side) which cope well with shrinkage and burn off in firing

I do hope this helps and wish you success with your sculpture

Christine

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I just did a workshop in the UK where the instructor uses bubblewrap scrunched into pillow shapes or what ever, surrounds it with chickenwire and covers with paperclay.

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Thanks, all. Anthony, I'm using Laguna c.6 porcelain, but plan to only fire to cone 5 (sag issue). I thought about a tube form, so your advice helps solidify that idea for me. I do know I'll need to be extra careful at joins to really smooth. Part of my brain still wants to push it and see if I can do it all hollow. I'm up to about 30 lbs. currently, so it will ultimately be around 50-60 lbs. Marcia, I think you're right, plus I started at the feet (tiny area where the weight concentrated). My second attempt I now have the torso set and will start on the extremities in the next few days. Christine and Riorose, I'd forgotten about the internal removal forms; thanks for reminding me. I had a teacher using Vermiculite in panty hose, which could be poured out after the shape had set up enough - d'oh! Sometimes I fear my brain is more interested in mirroring that of Homer Simpson instead of retaining useful information. All this is quite helpful, and I'll be utilizing your suggestions. Thanks again.

Rae Reich likes this

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I had a former student, Tana Patterson, who went on to do life size or bigger sculptures. She coil built them. She separated sections as she built up by using newspaper to separate the edges...and just kept going. SHe came back to teach part time while I was chairing the dept. She was very fast in building these in my opinion. I will see if I have a pic to send you. One piece was featured in the book Ceramic Design.<span class="Apple-style-span" style="font-family: Helvetica; "> </span>

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I had a former student, Tana Patterson, who went on to do life size or bigger sculptures. She coil built them. She separated sections as she built up by using newspaper to separate the edges...and just kept going. SHe came back to teach part time while I was chairing the dept. She was very fast in building these in my opinion. I will see if I have a pic to send you. One piece was featured in the book Ceramic Design.<span class="Apple-style-span" style="font-family: Helvetica; "> </span>

 

 

Thanks; I'd be interested in seeing that. My studio, despite being in NOLA, dries my clay out quickly, so I'm constantly spraying slabs and pieces. I've got the parts for the current piece wrapped in 5 plastic bags, with damp cloth on that, and it's still iffy. It makes smaller pieces tempting.

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Dear all,

 

Is it possible to leave a thick cardboard tube inside a piece when biscuit firing. It is a dense, 0.5cm thick cardboard tube left over from a roll of fabric. We have been making clay heads and a couple of students forgot to take out their cardboard supports and they're now stuck!

 

I'm scared that they might blow up the kiln!

 

Heather O

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cardboard will burn before anything in it could possibly "blow up".  you might find some ash residue where the cardboard was.  the real problem with cardboard armatures is that the clay may shrink around it and crack.  that happens LONG before it is ready for firing.

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oldlady is spot on.  The cardboard will burn out, with no issues, but the clay could crack, when drying.

 

Usually, when I use supports, or have students do so, we remove them once the clay has set a bit.  Also, I always go a bit looser, when wrapping or draping the clay, to prevent the shrinking so much, that I can't remove the support(s).

 

I have used a cardboard grid support inside a thinner slab base for a sculpture.  The figure, that made up the majority of the sculpture, put a lot of weight over the middle, so I knew it would need support.  The cardboard didn't cause any cracks, when the piece dried.  It must have compressed enough, that it wasn't an issue.  But the clay I used didn't shrink a whole lot either.

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Try wrapping the cardboard with a single layer of paper (newspaper)not stuck on the tube. It makes the tube easy to pull out without it sticking to the clay. If the paper won't come out no problem of it causing the clay form to crack while drying & it can be left in during firing if necessary, but will usually pull out easily.

Joy

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Expect smoke when you fire the kiln . . . once you get past 481F, all the paper is burned out.  Maybe leave the kiln lid propped open. 

 

For my cardboard tubes used for forming vases and cylinders, I put them in a knee-high nylon sock, tie up the end.  Clay does not stick to the sock.

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Thanks all!

 

I do usually use Joy Pots' technique of wrapping the cardboard tube loosely in newspaper so that it can slide out easily, however two of my students forgot to remove the cardboard at the end of the lesson and by the following week the clay had shrunk around it.

 

The nylon sock idea sounds great - thank you Oldlady and Bruce!

 

Have a great weekend everyone!

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