Snail Scott on sat 30 nov 02
At 12:25 AM 12/1/02 +0000, you wrote:
>...fires to cone 10, reduction in a gas fired kiln. She uses 580 porcelain
>...The bottoms of the pots or
>footrings stay on the shelf after firing.
Yep, this happens a lot with porcelain. It's
often vitreous enough all by itself that it
can stick to shelves with no help needed from
glaze drips! Many people mix a bit of alumina
into their wax for use on footrings.
-Snail
Paul Herman on sat 30 nov 02
Lela,
I think the phenomenon you describe below is known as "plucking".
You say that "the shelves are clean".
Do you mean that the shelves have no kiln wash on them?
If they don't, the clay can fuse to the shelf and tear loose during the
cooling cycle. Some cures might be to use kiln wash on the shelves,
and/or alumina wash on the foot, or wads to support the piece. After a
few ^10 firings, kiln wash can get pretty sticky, so watch out. A fresh
coat is more effective.
IMHO, the most elegant solution is to use wads, though it takes some
extra time. I encountered this problem with my new white stoneware body.
The clay is so vitreous that it will fuse to almost anything it touches,
excepting wads or alumina. I like wads.
Addendum, wadding recipe:
by weight,
1 fireclay (I use Lincoln)
1 kaolin
1 grog or silica sand
fine sawdust to taste
good luck,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
lela martens asked:
> A fellow guild member asked me to put this problem before you.
> She fires to cone 10, reduction in a gas fired kiln. She uses 580 porcelain
> and 443 dark Plainsman clay, as she always has. The bottoms of the pots or
> footrings stay on the shelf after firing. The shelves are clean, as are the
> bottoms of the pots, no running glazes.
> She re-vamped her kiln from updraft to downdraft and since she has done
> that, an un-even layer of clay is left behind on the shelf.
> Does anyone know why this would happen or how to solve the problem?
> Thanks, Lela
lela martens on sun 1 dec 02
Hi All,
A fellow guild member asked me to put this problem before you.
She fires to cone 10, reduction in a gas fired kiln. She uses 580 porcelain
and 443 dark Plainsman clay, as she always has. The bottoms of the pots or
footrings stay on the shelf after firing. The shelves are clean, as are the
bottoms of the pots, no running glazes.
She re-vamped her kiln from updraft to downdraft and since she has done
that, an un-even layer of clay is left behind on the shelf.
Does anyone know why this would happen or how to solve the problem?
Thanks, Lela
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Ron Roy on mon 2 dec 02
The clay is fusing to the shelf - use kiln wash as a barrier -
20 or 30% ball clay the rest alumina hydrate or calcined alumina hydrate
will do the trick.
Waxing with Alumina in the wax will probably work as well - a couple of
spoonfulls in a cup of wax - just on the bottom of the foot. Keep the wax
well stirred.
RR
>Hi All,
>A fellow guild member asked me to put this problem before you.
>She fires to cone 10, reduction in a gas fired kiln. She uses 580 porcelain
>and 443 dark Plainsman clay, as she always has. The bottoms of the pots or
>footrings stay on the shelf after firing. The shelves are clean, as are the
>bottoms of the pots, no running glazes.
>She re-vamped her kiln from updraft to downdraft and since she has done
>that, an un-even layer of clay is left behind on the shelf.
>Does anyone know why this would happen or how to solve the problem?
>Thanks, Lela
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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