Cynthia Bracker on tue 21 sep 04
Susan,
One of the most important things I can remember my dad saying (Mom says
it a lot too) is that CLAY HAS A LONG MEMORY. Anything you do to it
from leather-hard to bisque can affect the finished product. Often,
these things don't appear until after the glaze firing. Platters,
whether thrown or handbuilt are one of the biggest examples of this, I
think because of the large amount of "unsupported" clay beyond the
foot. Porcelain (It is happening with the porcelain, not the terra
cotta, yes?) is especially prone to this because of its soft nature
during the firing (consider wedging in some molochite for strength).
Think about how you load them into the kiln (for the bisque). Does the
warpage seem to mimic where you held the piece to load it? When else
are you touching it during the drying process? (leatherhard is the worst
time to touch it). How slowly are you drying them?
I don't think you will be more apt for warpage with re-used clay. Next
time you're in Lawrence, bring a piece or two for Mom to look at. She's
pretty good at figuring out the cause, especially from a visual.
Cindy Bracker
Susan Speck wrote:
>wondering if there was a way to keeping warping to a minimum in slab built
>plates. I always roll them on the slab roller and place them over a thrown
>plate form or over a bucket with cloth over the opening to get a nice
>curve. They warp during a glaze firing, never the bisque. Sometimes I
>rewedge an ugly plate before even let it dry. I use the clay again for the
>next plate. Am I apt to get warpage if I re-use the clay? Am I not wedging
>the clay enough? Is soemthing happening during the firing? Any help would
>be appreciated.
>
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