Roger Korn on sun 11 apr 04
I have noticed this sudden stiffening as well, but being unable to explain it, thought it
was just my imagination. Michael, have you also noticed that this "stiffened" clay is more
plastic than you expected for THAT clay at THAT stiffness? And throwing-wise, you can use
less water/slip and pull quite a bit higher? It is as though there is a definite threshold
where the clay platelets suddenly decide to align, rather than a steady improvement of
alignment with more wedging, as I note with conventional rams-head, spiral, or foot wedging.
Vince and all: any thoughts about this phenomenon?
Roger
Michael Wendt wrote:
Date: Fri, 9 Apr 2004 22:04:59 -0700
From: Michael Wendt
Subject: Re: : Stack & Slam wedging was StaRe: Wedging Table Height
Ivor,
I have noted only that my clay becomes stiffer around 230
layers which is contrary to the usual wisdom that wedging
softens clay.
I would welcome conjecture as to why.
My own theory is that packing begins around then with the clay
acting like mortar to neat stacks of bricks which increase the load
bearing character of the clay. My tests with the softness tester
confirm what I can feel with my hands as I wedge. The clay suddenly
becomes much stiffer around 28 - 30 doublings. The device measures
nearly twice the load bearing value of the clay before the effect
occurs.
I also do not detect any torsional effects when I throw ("S"-
cracks) nor
do I need to pin tool the lip when done as the uniformity of the body is
unmatched by any other wedging method I have tried.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
www.wendtpottery.com
--
McKay Creek Ceramics
In OR: PO Box 436
North Plains, OR 97133
503-647-5464
In AZ: PO Box 463
Rimrock, AZ 86335
928-567-5699
Linda Ferzoco on mon 12 apr 04
I bought one of the Chinese pounders from Chinese Clay Art a few months ago and use it to compress the slabs of clay before I roll them out. Is it possible that this technique is also aligning the clay particles? I haven't tested whether the clay is stronger when I do this, but I've been told that's what happens.
In any event, it's satisfying, so I'll likely continue to do it.
Linda
Pacifica, California
Roger Korn wrote:
I have noticed this sudden stiffening as well, but being unable to explain it, thought it
was just my imagination. Michael, have you also noticed that this "stiffened" clay is more
plastic than you expected for THAT clay at THAT stiffness?
Michael Wendt on mon 12 apr 04
Roger,
I can pull walls much higher with clay that is stack and
slam wedged 2^30. I think the increase in strength is
real and as I said, I attribute it to a more ordered
structure. Consider that a piece 3" tall with a billion
layers requires each individual layer to be only
3/1,000,000,000 of an inch thick. If my smaller particles
are 2/1,000,000 of an inch thick, then they have been
subjected to flow in a laminar sheet and are very likely
approaching a semblance of order.
Someone asked about the introduction of air during
stack & slam and I avoid it by keeping the faces of
the joined surfaces devoid of indentations from my
fingers.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
wendtpot@lewiston.com
www.wendtpottery.com
Roger wrote:
I have noticed this sudden stiffening as well, but being unable to explain
it, thought it
was just my imagination. Michael, have you also noticed that this
"stiffened" clay is more
plastic than you expected for THAT clay at THAT stiffness? And
throwing-wise, you can use
less water/slip and pull quite a bit higher? It is as though there is a
definite threshold
where the clay platelets suddenly decide to align, rather than a steady
improvement of
alignment with more wedging, as I note with conventional rams-head, spiral,
or foot wedging.
Vince and all: any thoughts about this phenomenon?
Roger
Ivor and Olive Lewis on tue 13 apr 04
Dear Linda Ferzoco,
I have just posted a message which may answer your question. I am sure
flakes of clay move to shape themselves around the much more bulky,
chunky bits of rock in a clay recipe. I am sceptical that clay
crystals align in parallel bedded sheets.
Whenever I pound clay or hit it, it deforms but retains the same
specific volume. It is not compressed. I imagine pounding clay might
make air bubbles migrate along planes of weakness and eventually pop
out. but the clay would flatten into a sheet as I did so.
When people make claims for a tool, a good ploy is to ask how they
know these things. Having such knowledge gives a user confidence.
Best regards,
Ivor Lewis. Redhill, South Australia
Linda Ferzoco on tue 13 apr 04
You have a good point about the specific volume. I wonder though why generations of Chinese potters have used the technique. I also wonder why we wedge clay that has come from some industrial machine that applied far more force than I can.
I don't throw clay on the wheel, so perhaps I'm not sensitive to the nuances of behavior that occur in that circumstance.
Thanks for the response. I'm following this thread with interest. Although I seem to have missed the detailed description of the stack and slam method, I understand the concept.
Linda
Pacifica, California
Ivor and Olive Lewis wrote:
Dear Linda Ferzoco,
I have just posted a message which may answer your question. I am sure
flakes of clay move to shape themselves around the much more bulky,
chunky bits of rock in a clay recipe. I am sceptical that clay
crystals align in parallel bedded sheets.
Whenever I pound clay or hit it, it deforms but retains the same
specific volume. It is not compressed. I imagine pounding clay might
make air bubbles migrate along planes of weakness and eventually pop
out. but the clay would flatten into a sheet as I did so.
When people make claims for a tool, a good ploy is to ask how they
know these things. Having such knowledge gives a user confidence.
Best regards,
Ivor Lewis. Redhill, South Australia
______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
| |
|
