Nancy Galland on thu 21 jun 01
I am getting discouraged and I wonder if anyone out there can help figure
out what is happening to my oblong shaped plates. They warp a lot. If you
have the attention for it, here are the details:
I am working with cone 6 porcelain. I had been using stoneware, which
hardly ever warped, but since the dioxin news, I have not been able to find
a stoneware that has no ball clay.
I slab roll it ( a Bailey, with 2 rollers), cut it to size, smooth off the
canvas marks with a plastic rib, put a cloth over it, flip it, smooth that
side; then I place a bisqued mold over it and flip the sandwich over so the
slab rests in the mold. I then smooth out the bottom, pressing around the
flat area with a damp sponge. I let that set for several hours and then
remove the plate from the mold by holding a flat piece of styrofoam under
the plate and flipping it upside down. I let it dry under plastic overnight
like this. The styrofoam covers the whole flat portion. I then finish the
drying on plastic waffle board that is used for fluorescent lights,
recommended by clayarters. Some will warp in the drying, even thought I am
doing everything I know to avoid it.
Those few that don't warp then, will warp in the bisque.
The bisque: I was advised by the tech consultant at the place where they
make this clay to bisque to cone 04. I usually use plate setters but they
may be causing me more problems than they are worth.
The Plate setters: the design of these setters is such that they rest on 3
built-in legs, and the flat area is a circle, maybe a 2" rim, with a
hole(3"?) in the middle. They stack. My oblong plates fit on them
perfectly. But never have I used them that the plates didn't warp. At first
I was rolling the porcelain 5/16th " thick; a glaze firing left them sunken
in the middle, bowled out where the hole is. Most plates had 4 feet but
some did not - there seemed to be no difference in the slumping.
I made another batch which was rolled 7/16" and 3/8" thick. Out of 9 made,
2 survived warpage during drying. For the bisque,I put these plates on the
plate setters, just 2 deep. One warped which had no feet. One that had
feet did not warp.
I also have a very hard time with feet. I have tried it seems every
possible type of foot but the warping makes the plates unstable on the
table...they will rock if you press opposite corners. I am losing my grip
on this, and I have lots of orders for them.
Is this too stressful a shape for porcelain? I hope someone can help -
Thanks - Nancy Galland
Craig Dunn Clark on fri 22 jun 01
Nancy, bring me up to date here. What dioxin news and what does it have
to do with ball clay?!? I use OM-4 in my clay body as well as my glazes.
As far as the porcelain goes, it is far more temperamental than
stoneware ever even thought about being. Dry it sloooooowwwwwwly and evenly.
Use grog, silica sand or wading on the kiln shelf.
Keep in mind that porcelain has a "memory" and needs to be treated and
handled as such. Because of this it is often best to handle unbisqued ware,
especially platters, as little as possible.
When you flip them use a bat on top as well as the bottom so that they
are stressed as little as possible. Also, try and keep the rims covered or
wrapped a little more tightly than the rest of the piece so that the pot
dries evenly.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "Nancy Galland"
To:
Sent: Thursday, June 21, 2001 12:57 PM
Subject: warping woes
> I am getting discouraged and I wonder if anyone out there can help figure
> out what is happening to my oblong shaped plates. They warp a lot. If you
> have the attention for it, here are the details:
> I am working with cone 6 porcelain. I had been using stoneware, which
> hardly ever warped, but since the dioxin news, I have not been able to
find
> a stoneware that has no ball clay.
>
> I slab roll it ( a Bailey, with 2 rollers), cut it to size, smooth off
the
> canvas marks with a plastic rib, put a cloth over it, flip it, smooth that
> side; then I place a bisqued mold over it and flip the sandwich over so
the
> slab rests in the mold. I then smooth out the bottom, pressing around the
> flat area with a damp sponge. I let that set for several hours and then
> remove the plate from the mold by holding a flat piece of styrofoam under
> the plate and flipping it upside down. I let it dry under plastic
overnight
> like this. The styrofoam covers the whole flat portion. I then finish the
> drying on plastic waffle board that is used for fluorescent lights,
> recommended by clayarters. Some will warp in the drying, even thought I am
> doing everything I know to avoid it.
> Those few that don't warp then, will warp in the bisque.
> The bisque: I was advised by the tech consultant at the place where they
> make this clay to bisque to cone 04. I usually use plate setters but they
> may be causing me more problems than they are worth.
>
> The Plate setters: the design of these setters is such that they rest on 3
> built-in legs, and the flat area is a circle, maybe a 2" rim, with a
> hole(3"?) in the middle. They stack. My oblong plates fit on them
> perfectly. But never have I used them that the plates didn't warp. At
first
> I was rolling the porcelain 5/16th " thick; a glaze firing left them
sunken
> in the middle, bowled out where the hole is. Most plates had 4 feet but
> some did not - there seemed to be no difference in the slumping.
>
> I made another batch which was rolled 7/16" and 3/8" thick. Out of 9 made,
> 2 survived warpage during drying. For the bisque,I put these plates on the
> plate setters, just 2 deep. One warped which had no feet. One that had
> feet did not warp.
>
> I also have a very hard time with feet. I have tried it seems every
> possible type of foot but the warping makes the plates unstable on the
> table...they will rock if you press opposite corners. I am losing my grip
> on this, and I have lots of orders for them.
>
> Is this too stressful a shape for porcelain? I hope someone can help -
> Thanks - Nancy Galland
>
>
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Wade Blocker on fri 22 jun 01
Nancy,
I think that you do not allow the clay to sit in your bisque mold for
enough time. When I make my plates they sit in the mold for at least
several days, covered with plastic. I do turn the plastic over so that the
moisture which condenses on it can dry. My local climate it relatively dry,
and if you live in an area that is humid, I would allow extra time for your
clay to harden in the mold.The thinner the clay object the more apt it is
to warp.Wedging some very fine grog into the clay will help prevent
warping.
Try bisque firing your plates upside down on shelves that have a thin
layer of silica sand on them (the sand acts like roller bearings)
If you use porcelain you cannot have the slabs too thin for what you are
making. Again grog might be your answer. The main thing is to be patient
and not hurry the setting up and drying time in your mold. Mia in hot ABQ
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