WJ Seidl on thu 22 mar 07
You're right Dave, it was Matt Katz, and not Dr. Carty.
My apologies to those two excellent presenters.
Too many things to do, too little sleep.
Best,
Wayne Seidl
(wiping egg off my face...)
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Dave
Finkelnburg
Sent: Thursday, March 22, 2007 4:36 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Plasticty of Clay Bodies--Long!
Hi all!
I've been following the discussion about the NCECA
presentation on clay bodies. I think the news from
that session is the most exciting thing to come out of
NCECA in my experience.
In his presentation Thursday morning, Matt Katz said
he believes he can make a porcelain clay body that is
as plastic as a stoneware body.
SNIP for space
I hope this provides a little added information on
one exciting NCECA session.
Dave Finkelnburg
Dave Finkelnburg on thu 22 mar 07
Hi all!
I've been following the discussion about the NCECA
presentation on clay bodies. I think the news from
that session is the most exciting thing to come out of
NCECA in my experience.
In his presentation Thursday morning, Matt Katz said
he believes he can make a porcelain clay body that is
as plastic as a stoneware body.
This I will believe when I can get my hands on the
clay and try it, but at the very least I believe the
research Katz and Dr. Carty are doing in this area may
achieve a real breakthrough for artists working with
clay.
First, though, what do we mean when we say
"plasticity?" We are talking about the ability of a
clay body to resist cracking when deformed. Whether
you extrude the clay with a machine, or between your
fingers on a wheel, or press it into a mold, or make a
slab and stretch and alter that, plasticity is that
property of the body that lets you alter its shape
without having the clay crack and break.
How do we measure plasticity? As Richard Aerni
said, by how it feels in his hands, or as Dannon Rhudy
said, by how well it stretches into handles. In other
words, by feel. As you can imagine, the "by feel"
method is subjective. However, I don't know of a
better method to compare plasticity of clay bodies.
There is a machine designed to test clay body
plasticity. It's called a shear cell and is
expensive, difficult to use, and I don't know that it
provides results useful to artists.
When he spoke early Thursday morning, Katz said he
had found a correlation between density of a dried
clay body and the plasticity of the body when wet. He
did this, he said, by getting an optimum mix of
particle sizes in the body. He found that if he made
a body too dense, it could still be worked by
industrial machines (jiggered, jollied, RAM pressed)
but was too "stiff" for hand forming.
He did not say this exactly, but implied, that the
plasticity influenced by varying the moisture of the
body though the normal range of 19 to 24% water by
weight was not significant compared to the plasticity
influence from dry density.
So, what I took away from this is whether you add
bentonite or Vee-gum T, use ball clays, add organics,
age for years, etc, Katz has found a way to adjust a
clay body recipe to make it more dense and thus to
improve plasticity of that body even more. He added
he was seeing these benefits within 48-hours of mixing
the clay body and extended aging did not seem to have
any noticeable effect.
Now Katz was talking ONLY about clay bodies made
from dry ingredients but mixed with a lot of water
into a fairly fluid slurry and then dewatered with a
filter press and pugged or kneaded to throwing
consistency. He was very clear that he did NOT use a
Soldner-type clay mixer.
I do wonder, how many of the comments on the list
this week about the benefits of aging on plasticity
apply to clay bodies made in Soldner-type mixers? Few
of us have access to wet-processed clay bodies that,
as mined, are formable and fire to between cones 5 and
10 or so.
I hope this provides a little added information on
one exciting NCECA session.
Dave Finkelnburg
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Michael Wendt on thu 22 mar 07
To add to what Dave has written:
A few years ago, Plainsman Clays and Tony
Hansen were testing Helmer Kaolin to see
if it could be of value as a throwing body.
They hauled 90 tons north and were dismayed
to find that the clay bodied they made with Helmer
were very absorbent even at cone 10.
Tony called me and asked if they had
received clay from a different part of the deposit,
perhaps one more refractory.
The mining method is always the same...
Vertical face, to assure consistent composition.
The reason I thought their bodies were so much more
porous and absorbent was they ground the clay
fine enough to pass 50 mesh dry and mixed the
clay body from dry powder.
The clay porosities I had given them for my
clay body formulation were from wet slurried
clay.
We blunged all the ingredients, tray dried them
and then ground the cakes in the hammer mill.
The body was less than 1% porous using this
method and it was not critical to catch the clay
cakes at a plastic state.
The dry grind was used in conjunction with
additional blunged slip to make a clay body
that was both plastic and very low absorbency.
Now we mix with post cyclone air float from
the bag house dust collector.
The clay is so fine it really does float on air.
As a result, we get the same porosity we used to
get by wet milling with the new dry blended
body.
For the record, we mix in a high shear mixer
which kneads the clay into the side of the
mixer tub with a great deal of force as it
also drags it along the tub to shear it.
works great and is very fast.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
USA
208-746-3724
http://www.wendtpottery.com
wendtpot@lewiston.com
Lee Love on fri 23 mar 07
On 3/23/07, Michael Wendt wrote:
> to find that the clay bodied they made with Helmer
> were very absorbent even at cone 10.
This is good to know. Mogusa tsuchi, clay traditionally used in Mino
for Shino is absorbent to cone 13. At cone 11 it is similar to Raku or
bisque ware. I have added Mashiko nami to help it a little.
It is why American Shino pots don't "feel" right to the Japanese.
They say that the clay has "a taste" in the original pots.
Is it possbile to get unrefined (non-air floated) helmer?
The other aspect of Mogsua is the organics in it. Industrial
processing "kills" the clay.
I would like to experiment when I get to Mpls. I am interested
in a more traditional clay for teaware only. I should also bring
some mogusa to be analyzed.
Anybody have a web page for a lab? I could get the lab work
done now so I have a head start.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
Ron Roy on sat 24 mar 07
Hi Dave,
I did have access to clays mixed as a slurry and filter pressed at one
point - Tucker has bought another clay company that used the process - he
found that potters were unwilling to pay for the added expense of producing
bodies that way.
They did improve with age by the way.
Tuckers mixes all bodies using an Irex mixer - a huge improvement over the
usual wad mills used by most clay makers in North America. I would be most
interested in knowing how to test the bodies made with the Irex to see how
well they are mixed.
I would expect the high speed mixing to be excellent compared to slurry
mixing - in terms of mixing materials - got any sort of tests I can do?
There is no doubt that - even though the clays are designed to be usable
straight out of the mill - they do start improving immediately.
The standard test potters use to determine workability is a coil wrapped
around a finger. If the coil cracks - you know the clay is short and/or too
dry and may not do all that is expected of it.
RR
> Now Katz was talking ONLY about clay bodies made
>from dry ingredients but mixed with a lot of water
>into a fairly fluid slurry and then dewatered with a
>filter press and pugged or kneaded to throwing
>consistency. He was very clear that he did NOT use a
>Soldner-type clay mixer.
> I do wonder, how many of the comments on the list
>this week about the benefits of aging on plasticity
>apply to clay bodies made in Soldner-type mixers? Few
>of us have access to wet-processed clay bodies that,
>as mined, are formable and fire to between cones 5 and
>10 or so.
> I hope this provides a little added information on
>one exciting NCECA session.
> Dave Finkelnburg
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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