Susan Speck on mon 20 sep 04
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.
Catherine Yassin on tue 21 sep 04
In a message dated 9/20/2004 7:25:19 PM Central Standard Time,
llywhite1906@SBCGLOBAL.NET writes:
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.
I would try everything that Vince suggested and in addition to that DRY
SLOWLY. I had the same problem with slab plates. They would look fine after the
bisque but were transformed into something totally different during the glaze
firing. Someone asked me if I had dried them too quickly and I realized then that
I had actually dried them very quickly, something I do with my wheel thrown
pots. But I never had warpage with the wheel thrown ones.
-Cat Yassin
San Antonio
Ron Roy on thu 23 sep 04
Hi Susan,
Stretched clay always shrinks more than compressed clay - usually the out
side part of a slab is stretched and the inside compressed - if you can
compress the outside clay between rolling it you will help solve the
problem.
You can see this by taking a slab - cutting it up into say 4" squares - and
drying and firing it - the tiles that stay most flat will be from the
centre of the slab.
If you only used the centre part of the slab you would help solve the problem.
The effect is made worse with clays that are too plastic and/or over
vitrified in the glaze firing.
Testing the clay you use for shrinkage and absorbency will help you
understand - in this case because it is only happening in the glaze firing
I would think the clay is overfired.
If you need to know how to test clay let me know.
RR
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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