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slab warpage


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#1 acg

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Posted 01 November 2012 - 11:54 AM

Hi,

A friend and I share a kiln together. She is having problems with warping in the bisque.

Clay body - Tacoma Clay Art paper clay
firing - ^06 using the Skutt firing schedule
Thickness - 1/4/ to 1/2 ins.
Tossed and rolled with a rolling pin
Design made on drying board
Dried to soft leather hard then: either a second sheetrock board is put in top or weights put on the 4 corners
At leather hard put in a convection oven. on the oven racks and dried for 12 hr at 170 F
Placement in kiln - larger pieces stacked flat on the top shelves, spanned the kiln shelves these had the most warpage
smaller pieces stacked leaning against the shelf
the smaller pieces stacked flat on the bottom shelf seems to have the least warpage


These forums are so great. Thanks for all your help

acg


#2 Marcia Selsor

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Posted 01 November 2012 - 01:10 PM

I put my large raku slabs on to sheet rock lined with newsprint paper. I roll them on my slab roller. Slide a board underneath the slab mat, place the newsprint on top of the slab, place sheet rock on top of that, then flip the whole thing tightly sandwich to avoid any disfiguring of the slab.
Once flipped, I remove the board and slab mat, attach hanging nubs, wax the edges , slide the sheet rock and slab into my bakers rack covered with plastic and don't move it til it is dry.I bisque them on edge and fire them on edge as well. See photo from Raku Masters at Dan Finch's.. I think you are handling them too much especially before leather hard.
Marcia

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#3 Cass

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Posted 01 November 2012 - 01:12 PM

1 sided tiles? score the back...i carve a grid with a wide trimming tool a bit less than 1/2 the tile thickness...look at the back of a factory tile to see what i mean, little raised squares are all that is left at full thickness

slow drying under plastic for 1 week plus, skip the oven (never heard of that).. the slower the better

not familiar with that clay body, but that could be a factor...maybe test adding some sand or grog

#4 Chris Campbell

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Posted 01 November 2012 - 04:30 PM

When you get to the design made on drying board stage .... the next step for me is to drop the board to the ground from waist height twice.
Then don't touch your slab again until it is dry. You can dry it in full sunlight and it won't warp.

Chris Campbell
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