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Some Advice On My Latest Disaster Please


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#1 capt don

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Posted 15 August 2013 - 03:11 PM

I made a free form platter with macabee cone 5 clay and bisque it to cone 04, everything fine at this point. I gave it 3 coats of western cone 5 glaze and fired to cone 5. I put a  3 legged stilt with the pins in it that they sold me at the clay place. problem is when I opened the kiln, the glaze was beautiful but the platter essentially flopped. I guess it was from the support in the center of the bottom while sitting on the kiln plate. How do you keep this kind of stuff from happening? If I had not put the stilt under it and just sat it on the shelf with kiln wash on the shelf would it have still flopped?  Pic's attached.

thanks again for everyone's patience.  capt don

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#2 neilestrick

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Posted 15 August 2013 - 03:22 PM

Something that thin and flat will need many stilts to support it, and even then it may sag around the stilts. I recommend making it a little thicker and putting a foot ring on it that supports it well, or use a ton of stilts, or leave the bottom unglazed and lay it directly on the kiln shelf, maybe with a little silica sand under it to help it move.


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#3 Pres

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Posted 15 August 2013 - 07:35 PM

It could probably use a rim thickener also, maybe a blended coil. As Neil said, it would help to hane foot ring, but think about diameter sise anheight. D. Size for proper support, height for design.

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#4 Denice

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Posted 16 August 2013 - 09:11 AM

Another thing that might help is additional compression along with addition of coils, most people thick of compression when throwing but it also needed with slab work.  Denice.



#5 Isculpt

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Posted 17 August 2013 - 12:24 AM

Denice, can you explain your answer a little more thoroughly?  thanks....



#6 clay lover

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Posted 17 August 2013 - 07:55 AM

If I had tried the same thing, I expect I would have gotten the same results. Sorry.

These longer than wide forms can be difficult to get flat and they can warp even when laid flat on the kiln shelf.  I can't think of anything that would keep it flat with only the 1 center support.  Try putting a rim on it and a foot ring under it that is about 3/4 the size of the total form.  Maybe.... but probably not.

Other option, put a rim on it and wax up the sides 1/4", then lay it flat and see what happens.    



#7 Biglou13

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Posted 17 August 2013 - 08:35 AM

In another Post. "pounding vs rolling" we talked about compressing slab via pounding rolling or both. Well think of getting more clay Into same area. Or increase density of clay. Try pounding clay first, then throw flat slab in multiple directions, then roll out gradually in multiple directions. Then dry slowly, Painfully slowly, covered in plastic. Drying a flat piece like that presents problems in un even drying which can lead to warping.

If you have to have bottom glazed. Try a whole bunch of of those 3 pin stilts?

So you solution is multi fold.
Solve the uneven drying
Solve the stilting issue.
Solve the structural issues (Foot)

Easy solution.
Don't glaze bottom or sides. Make thicker, Make better slab, dry slow, fire flat on kiln floor.
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#8 capt don

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Posted 17 August 2013 - 10:14 AM

Thanks for everyone's help. I do wedge the clay well and then put it thru my Baily mini slab roller so it's nicely compressed, I guess I just have so much un-supported area and the clay gets to it's softening point at cone 5 and slumps. I'll try giving it support around the edges and see what happens. I bought a plate similar to the one that I made a couple years ago and always wanted to get around to making one. I can't find any pin marks under the flared sides and it's glazed around the edges and bottom to almost where the flat bottom is, wonder how that person did it without getting the flop.

#9 Chris Campbell

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Posted 17 August 2013 - 11:00 AM

Some clays are a lot more forgiving than others. You can build almost anything with them trouble free. Others ... which are usually the ones you like the best ..... give you a hard time with warping, sagging etc. I think it is the one rule of pottery that you will love the thing that punishes you most ... Or is that just a rule for us crazies who work with porcelain?

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#10 Mark C.

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Posted 17 August 2013 - 03:31 PM

I do not see these as a disaster but more as a boomerang with handles.

Just think down under mate.

Mark


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#11 Bob Coyle

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Posted 17 August 2013 - 04:09 PM

Don't worry about wedging or re working your clay. The trick on these thin forms is lots of support.  nothing else will keep them from sagging when fired from bisque to cone 5. A thin thrown bowl doesn't sag because the forces around the bowl are in tension and balanced. That is not true for hand formed platters.

 

Don't feel like the lone ranger... I lost my first platter too.






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