Jeff Lawrence on tue 3 aug 99
Hello all,
I recently found time to do some throwing and was trying for tall (for me)
pitchers. I started with pugmill pugs that had not been wedged in advance,
which seemed stiffish at first. Several times, I got cylinders up to about
20 inches on maybe three pulls, and then on the fourth pull they shrank on
me. The cylinders lost inches in height as they settled into an
ever-thickening base. Subsequent pulls just made matters worse. The bottom
wall, though it became twice as thick, was much softer and flabbier than
originally.
My conclusion was the throwing stimulated the clay thixotropically to relax
and liquify on me.
If that is the case, what solutions other than changing clay bodies (or
learning to throw better) might maintain the clay's rigidity?
If any other accounts suggest themselves, what are they and what does one
do about them?
TIA,
Jeff
Jeff Lawrence Sun Dagger Design
jml@sundagger.com Rt. 3 Box 220
www.sundagger.com Espanola, NM 87532
vox 505-753-5913 fax 505-753-8074
Michael Banks on thu 5 aug 99
Sounds like your clay has some soluble soda lurking in it Jeff. Probably
from nepheline syenite or soda-rich feldspar in the recipe. You could try
acidifying your throwing water to counter this, or alternatively wedging-in
a flocculent such as epsom salts or calcium chloride solution. A pH check
on the body using pH papers should give a clue to the problem. Most throwing
bodies benefit from being slightly acidic (pH <7). What clay are you using?
Some North American lurkers may be able to provide it's ideal pH.
Cheers,
Michael,
Nelson,
New Zealand
----- Original Message -----
> ----------------------------Original message----------------------------
> Hello all,
>
> I recently found time to do some throwing and was trying for tall (for me)
> pitchers. I started with pugmill pugs that had not been wedged in advance,
> which seemed stiffish at first. Several times, I got cylinders up to about
> 20 inches on maybe three pulls, and then on the fourth pull they shrank on
> me. The cylinders lost inches in height as they settled into an
> ever-thickening base. Subsequent pulls just made matters worse. The bottom
> wall, though it became twice as thick, was much softer and flabbier than
> originally.
>
> My conclusion was the throwing stimulated the clay thixotropically to
relax
> and liquify on me.
>
> If that is the case, what solutions other than changing clay bodies (or
> learning to throw better) might maintain the clay's rigidity?
>
> If any other accounts suggest themselves, what are they and what does one
> do about them?
>
> TIA,
> Jeff
>
>
> Jeff Lawrence Sun Dagger Design
> jml@sundagger.com Rt. 3 Box 220
> www.sundagger.com Espanola, NM 87532
> vox 505-753-5913 fax 505-753-8074
>
Dwiggins, Sandra (NCI) on fri 6 aug 99
Hey Jeff---
I've had the same experience and I thought it was something I was doing wrong
when I was throwing. It seemed that the clay would only support a certain
height and would go no higher, and each time I tried it got worse---just like
you describe. At first I thought I might be using too much water, but that
wasn't the problem. I'm so glad that someone else has had that experience!
The clay that I remember particularly when this first happened to me, was a
white cone 6 stoneware from Standard. It was so long ago that I don't remember
the number. However, it has happened after this, especially with clay that has
been recycled and pugged.
I, too, would appreciate knowing why this happens.
Sandy
Sandra Dwiggins
Sandra Dwiggins
Technical Information Specialist
Office of Cancer Information, Communication and Education
National Cancer Institute
National Institutes of Health
e-mail: sdwiggin@exchange.nih.gov
fax:301-480-8105
phone: 301-496-7406
-----Original Message-----
From: Jeff Lawrence [SMTP:jml@sundagger.com]
Sent: Tuesday, August 03, 1999 2:01 PM
To: CLAYART@LSV.UKY.EDU
Subject: thixotropical blues
----------------------------Original message----------------------------
Hello all,
I recently found time to do some throwing and was trying for tall (for me)
pitchers. I started with pugmill pugs that had not been wedged in advance,
which seemed stiffish at first. Several times, I got cylinders up to about
20 inches on maybe three pulls, and then on the fourth pull they shrank on
me. The cylinders lost inches in height as they settled into an
ever-thickening base. Subsequent pulls just made matters worse. The bottom
wall, though it became twice as thick, was much softer and flabbier than
originally.
My conclusion was the throwing stimulated the clay thixotropically to relax
and liquify on me.
If that is the case, what solutions other than changing clay bodies (or
learning to throw better) might maintain the clay's rigidity?
If any other accounts suggest themselves, what are they and what does one
do about them?
TIA,
Jeff
Jeff Lawrence Sun Dagger Design
jml@sundagger.com Rt. 3 Box 220
www.sundagger.com Espanola, NM 87532
vox 505-753-5913 fax 505-753-8074
June Perry on sat 7 aug 99
I would guess that the clay has most ingredients with smaller particle size.
To get the clay to hold up a good body would have some tooth to it using both
fine and coarser materials and well as some grog and/or sand. Fireclays
supply tooth and some have more than others. 200 mesh flint gives some tooth
and using a combination of fine particled and more coarser ball clays and
stoneware clays will also help.
If you love the claybody you're using, you can try throwing dry. After you do
your opening and first pull, dry your hands and throw dry. It takes practice,
but you can get some pretty thin walled, tall pieces throwing dry.
Years ago there was an article in Ceramic monthly of a young potter throwing
tall porcelain, very thinly, using the dry throwing method. You just have to
be very in tune, sensitive, to the feeling of the clay against your fingers
and it takes a bit of practice.
Regards,
June
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