Lester Haworth on fri 21 oct 05

Dan,
I stand corrected,
I am not a bread maker.
But I was taught to wedge my clay, not knead it.
Thanks for the bread education. You learn something new every day.

Les H.

-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Pfeiffer,
Dan R (Dan)
Sent: Friday, October 21, 2005 6:40 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: S-cracks...is clay actually compressed? Oh yah!


>>>I do not knead my clay, I wedge it! Kneading is for bread bakers who want
to
introduce air into dough. >>>

Bread bakers do not knead dough to put air in it! You knead dough to develop
the gluten strands in the dough that will hold the co2 that the yeast makes
and this will rise the dough. Only the worst types of machine make bread try
to introduce air in the dough.

I have been making bread for a great many more years than pots and one of
the odd things I have noted it that if you knead clay in the same way you do
dough it makes for a badly wedged clay and if you wedged dough like clay it
does on make a good ball of dough. Dough has a nice spring to it that clay
does not and while it may to useful to speak of kneading clay "like" dough
it is not the same motion. I find after doing a lot of wedging it is very
hard to go back to kneading my dough correctly.

Now that we have a pugmill no problem.:)

Dan & Laurel in Elkmont Al
Potters Council Members

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Ivor and Olive Lewis on sun 23 oct 05

Dear Bonnie,

Thank you for your support on this one.

I have also made observations similar to those you describe, that after =
an initial burst of spiral wedging a renewed burst of kneading after end =
to end inversion leads to a point in time where the clay seems to =
stiffen unexpectedly. I have an explanation but one would believe me =
(Consult Lawrence and West, 2nd Ed, p102, fig 7-6 ! and the penultimate =
paragraph on page 80)

But as to what is happening in the clay, I have an open mind, except for =
the observation, based on sectioning thrown billets of coned clay which =
have had tracer material introduced, (after the fashion of making Agate =
Ware but with purpose). Cross sections reveal Spiral Patterns develop =
are visible to the eye and that the edges between differing colours of =
clay show signs of turbulence and tearing.

Notions about pressure orienting clay crystals are hypotheses. I have =
yet to be shown or find Electron Microscope (SEM, Tunnelling etc.) =
images of a Wet Plastic Clay Body. Without such evidence anyone who =
promotes the idea is guessing.

I will send you some pictures of fractures in clay that I made =
yesterday, together with a commentary.

Best regards,

Ivor

2ley on sun 23 oct 05

From: "Vince Pitelka"
> Sometimes the results drawn from rational inquiry and practical experience
> are the most applicable and enduring. There is nothing absolute about
> conclusions extrapolated from an electronmicrograph. The scientific
> method
> is often severely flawed.

With all due respect to both sides of this discussion, I'd like to state
that it is entirely possible that both sides are both right and wrong.
Simply put, it would seem from all of the data given that the S-crack
problem is a multi-variate one. It would appear that, at first blush, this
problem has more than one possible factor causing the same crack, be it lack
of compression, too much water, and so on.

Vince, the problem isn't that the scientific method is flawed, it is that a
properly designed experiment has yet to be run. A properly designed
experiment would take in as many of the factors as seemed relevant, and
would also allow for the existence of a factor or factors that had not been
foreseen.

But your remark about the electronmicrograph was spot on, as they say. A
SEM photo can show us what is, and we can infer from that some theories of
how what is came to be, but it cannot do more than that. Whether the
platelets are or aren't aligned and perfectly flat when an S-crack happens
isn't the issue, the issue is how they came to be in the configuration that
they ended up in. And once more, a properly designed experiment would help
in determining that.

Until then, we're all full of guesses. My guess is that, to some extent,
all of the suggested causes of S-cracks are valid, and are compounded by
each other and other, yet undefined, variables.

Philip

Vince Pitelka on sun 23 oct 05

Ivor Lewis wrote:
"Notions about pressure orienting clay crystals are hypotheses. I have yet
to be shown or find Electron Microscope (SEM, Tunnelling etc.) images of a
Wet Plastic Clay Body. Without such evidence anyone who promotes the idea is
guessing."

But Ivor, that is much of what scientists do. They gather information, and
then make their best educated guess. Often, the level of certainty
presented as "proof" is based on a series of educated guesses, rather than
on indisputable facts. For anyone who has spent a long career in clay
observing the behavior of clay in thrown, coiled, and slab-built form, there
can be no doubt that the means of forming plastic clay creates a linear
grain structure, and that the subsequent shrinkage of the clay is greatly
affected by that grain structure. The "pressure orienting" that occurs when
we compress the bottom of a pot is simply one more example of this
phenomenon.

It is not necessary to see an electronmicrograph showing the linear
orientation of clay platelets to know absolutely that this is what is
happening when we work plastic clay.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/

steve graber on sun 23 oct 05

keep searching Ivor, that is much of what scientists do. they don't stop when they *think* they know the root cause. they keep looking & studying until they have truly convincing info. they actually continue to learn this way! ~ might even learn other stuff as well...

keep me posted~

see ya

steve


"It is not necessary to see an electronmicrograph showing the linear orientation of clay platelets to know absolutely that this is what is happening when we work plastic clay. Best wishes -- Vince"





Vince Pitelka wrote:Ivor Lewis wrote:
"Notions about pressure orienting clay crystals are hypotheses. I have yet
to be shown or find Electron Microscope (SEM, Tunnelling etc.) images of a
Wet Plastic Clay Body. Without such evidence anyone who promotes the idea is
guessing."

But Ivor, that is much of what scientists do. They gather information, and
then make their best educated guess. Often, the level of certainty
presented as "proof" is based on a series of educated guesses, rather than
on indisputable facts. For anyone who has spent a long career in clay
observing the behavior of clay in thrown, coiled, and slab-built form, there
can be no doubt that the means of forming plastic clay creates a linear
grain structure, and that the subsequent shrinkage of the clay is greatly
affected by that grain structure. The "pressure orienting" that occurs when
we compress the bottom of a pot is simply one more example of this
phenomenon.

It is not necessary to see an electronmicrograph showing the linear
orientation of clay platelets to know absolutely that this is what is
happening when we work plastic clay.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/

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Craig Clark on sun 23 oct 05

Vince Pitelka wrote:

>
>
> "............It is not necessary to see an electronmicrograph showing
> the linear
> orientation of clay platelets to know absolutely that this is what is
> happening when we work plastic clay........"
> Best wishes -
> - Vince
>
Vince, while I would side with the orientation argument that you are
making I must take exception with the manner in which you conclude your
argument. This smacks of what I would describe as moral sertitude.
Whenever I hear someone use the words absolute and know either in close
proximity or conjunction I am forced to take a double take and state
that I find it more than difficult to know anything with absolute
certainty. I'll stand with Ivor on his insistence that seeing is
believing, at least if described in terms of absolutes.
Just my two cents
Craig Dunn CLark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org

Vince Pitelka on sun 23 oct 05

> Vince, while I would side with the orientation argument that you are
> making I must take exception with the manner in which you conclude your
> argument. This smacks of what I would describe as moral certitude.

Craig, we've been through this before. Are you really saying that it smacks
of moral certitude because I am sure of myself about something? I am always
searching with an open mind, always trying to understand, but after almost
40 years of working clay in every conceivable way, it naturally gets to the
point where there are some things I am very sure of. That's a GOOD thing,
and the logical result of such a long search. One of the things I am very
sure of is the phenomenon of grain structure in clay - the alignment of
platelates resulting from the way in which the clay has been worked. It
corresponds with EVERYTHING having to do with the behavior of clay, and any
supposed evidence to the contrary has been shown to be unsubstantial and
unsupportable.

Sometimes the results drawn from rational inquiry and practical experience
are the most applicable and enduring. There is nothing absolute about
conclusions extrapolated from an electronmicrograph. The scientific method
is often severely flawed.
- Vince

Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/

Ivor and Olive Lewis on mon 24 oct 05

Dear Vince Pitelka,=20

You are correct. Scientists do make guesses, they are called =
"Hypotheses". And they remain in that form until someone devises an =
experiment to reveal evidence to support or refute the first assertion. =
If sufficient evidence is found which supports the hypothesis it may be =
accorded value by being termed a Theory. But it is still open to =
refutation.

The experiment I am calling for is to image samples of plastic clay that =
has been worked, but not allowed to dry. That might support your =
assertion or it might not. It may well prove that you are correct in the =
conclusions you have drawn from your observations. But it would be a =
fact that can be checked.

To support your assertions you have to show an image of the claimed =
phenomenon. You have also to rule out the presence of any other =
phenomenon that could produce the effects you have recorded from your =
common place observations.

Nice to discuss this with you.

Best regards,

Ivor

Tom at Hutchtel.net on mon 24 oct 05

This has been interesting but it doesn't, so far, seem to be gaining us much
ground. Philip is right, we need some hard data, real experiments. Ivor
has done a lot of this, some of which has been referenced.
And I agree with Vince, that with some knowledge of the structure of clay,
you can probably guess pretty knowledgably as to what's going on.
I'd like to focus back on two things I said some time ago, One is the fluid
nature of the material...and how when you're coning up the clay flows
through the hump and back down forming somewhat of a whorl as the outer clay
swirls (twisted by the friction of your hands) that moves back down into the
hump forming a very definite shear line as it does so. If you "compress"
the clay, or if the clay formula is right, the particles along those shear
lines rejoin...much like sticking a handle on a mug. Some clay don't rejoin
so readily.
Thy this experiment....cone up some clay without pushing the hump back down.
Take two or three 1/4 to 1/2 inch slices off and freeze them. You'll see
these shear lines open up.
Another sign of this whorl/shear line is when you use a finger to open the
center on a hump piece. You can usually actually feel the two sides of the
whorl. As long as they're there, you're going to get an s crack.
Now do the same centering and coning but this time rework just the top of
the cone up and down 2 or 3 times. Now take your slices. You'll probably
find those shear lines gone.
I'd suspect the same thing is going on in larger pieces, too (but I've only
had 12 years not 40, experience), the compression we speak of, as Vince and
other have said, is not really compressing the clay (making the volume
smaller and denser) but really just realigning the particles to get rid of
the shear lines.
I'm not sure we'll ever see microphotographs of this process since we can't
study it when we are throwing. I still submit that the clay is 2 different
materials, one (more or less solid and stable) at rest and one in motion (
really a thick fluid with the particles sliding over each other). The only
things we can study is the aftereffect of the motion. So we're probably
somewhat doomed to never really answering this except but what we can feel
when we throw.

Tom Wirt
Hutchinson, MN
twirt@hutchtel.net
www.claycoyote.com

Jim Murphy on tue 25 oct 05

Hi Ivor (et al),

Here's an interesting high-zoom video link:



Click on the "clay" icon [bowl] to see a high-zoom (over 12-million x)
"video" of a clay bowl's internal microstructure.

There's also a video of a ceramic high-Alumina sparkplug.

Now, if we can only get someone to zoom-in on a newly-formed "S-crack". ;o)

Best wishes,

Jim Murphy


on 10/24/05 1:51 AM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:

> The experiment I am calling for is to image samples of plastic clay that has
> been worked, but not allowed to dry. That might support your assertion or it
> might not. It may well prove that you are correct in the conclusions you have
> drawn from your observations. But it would be a fact that can be checked.

William & Susan Schran User on tue 25 oct 05

On 10/24/05 10:00 AM, "Tom at Hutchtel.net" wrote:

> the compression we speak of, as Vince and
> other have said, is not really compressing the clay (making the volume
> smaller and denser) but really just realigning the particles to get rid of
> the shear lines.

But couldn't both happen? That the clay particles are being realigned &
compressed?

>I still submit that the clay is 2 different
>materials, one (more or less solid and stable) at rest and one in motion (
>really a thick fluid with the particles sliding over each other). The only
>things we can study is the aftereffect of the motion.

Perhaps this should then lead us to the properties of thixotropic materials.
I've experienced the simple act of taking a stiff piece of clay, slamming it
on the wedging board and having it become softer.
Perhaps there is more than the additional water added to the clay during the
throwing process, we need to additionally consider our movement of the clay,
how it is manipulated.

Which leads us to the stretching and compression of the clay, yet again.


--
William "Bill" Schran
Fredericksburg, Virginia

John Jensen on tue 25 oct 05

I did a little experiment a few years back which I invite others to
replicate: I compared the shrinkage between two blocks of clay. Block A =
was
cut straight from the box...now wedging or any other treatment. Block B =
was
built up of multiple layers of slabs which had been rolled with a =
rolling
pin. The hypothesis was that the block made up of rolled slabs would =
shrink
more then the unprocessed block. I did find a significant difference, =
on
the order of 8 percent. This difference could be explained by the
realignment of clay particles and could be considered a form of "latent"
compression.

John Jensen, Mudbug Pottery
John Jensen@mudbugpottery.com
http://www.toadhouse.com www://www.mudbugpottery.com

-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ivor and =
Olive
Lewis
Dear Vince Pitelka,=3D20

You are correct. Scientists do make guesses, they are called =3D
"Hypotheses". And they remain in that form until someone devises an =3D
experiment to reveal evidence to support or refute the first assertion. =
=3D
If sufficient evidence is found which supports the hypothesis it may be =
=3D
accorded value by being termed a Theory. But it is still open to =3D
refutation.

Vince Pitelka on tue 25 oct 05

Ivor Lewis wrote:
"To support your assertions you have to show an image of the claimed
phenomenon. You have also to rule out the presence of any other phenomenon
that could produce the effects you have recorded from your common place
observations."

Dear Ivor -
I do appreciate your thoroughness and your scientific mind. But I don't
have to do any of those things. I am perfectly comfortable with the
theories of platelate orientation and grain structure as connected to
compression, drying shrinkage, clay memory, and other clay phenomena I have
been observing throughout my career in clay. Every behavior of clay in
forming and drying supports these theories. I have no reason to question or
dispute these theories, so there is no reason for me to prove anything. If
someone else chooses to disbelieve these theories, it is up to them to
gather evidence to disprove them.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/

steve graber on wed 26 oct 05

good - then don't read ivor's updates. while it may be shown by today's technology what you think is happening, is; it may also be shown some other phenomenon, or a deeper characterisitc is occurring. such reviews are always interesting to the open mind.

see ya

steve


ps - ivor: can you use smaller words please?




Vince Pitelka wrote: Ivor Lewis wrote:
"To support your assertions you have to show an image of the claimed
phenomenon. You have also to rule out the presence of any other phenomenon
that could produce the effects you have recorded from your common place
observations."

Dear Ivor -
I do appreciate your thoroughness and your scientific mind. But I don't
have to do any of those things. I am perfectly comfortable with the
theories of platelate orientation and grain structure as connected to
compression, drying shrinkage, clay memory, and other clay phenomena I have
been observing throughout my career in clay. Every behavior of clay in
forming and drying supports these theories. I have no reason to question or
dispute these theories, so there is no reason for me to prove anything. If
someone else chooses to disbelieve these theories, it is up to them to
gather evidence to disprove them.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/

______________________________________________________________________________
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.




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Earl Brunner on wed 26 oct 05

Now, now Steve, when Ivor is addressing something directly to you, sometimes
you answer.....
Vince's point is well taken, While Ivor's knowledge, approach and expertise
are appreciated and valued, he sometimes does dump stuff on you that can be
more than you want to do. In this case, it isn't the status quo that needs
to prove itself, but whatever one wishes to supplant it with.
I don't have to understand electricity, to use it and even work with it, I
just have to know what I can and can't do and still live. I don't actually
have to be a research scientist to make pots. I just have to know enough
science to get the job done, and maybe satisfy my curiousity.

Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of steve graber
Sent: Wednesday, October 26, 2005 7:29 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: S-cracks...is clay actually compressed? Oh yah!

good - then don't read ivor's updates. while it may be shown by today's
technology what you think is happening, is; it may also be shown some other
phenomenon, or a deeper characterisitc is occurring. such reviews are
always interesting to the open mind.

see ya

steve


ps - ivor: can you use smaller words please?




Vince Pitelka wrote: Ivor Lewis wrote:
"To support your assertions you have to show an image of the claimed
phenomenon. You have also to rule out the presence of any other phenomenon
that could produce the effects you have recorded from your common place
observations."

Dear Ivor -
I do appreciate your thoroughness and your scientific mind. But I don't
have to do any of those things. I am perfectly comfortable with the
theories of platelate orientation and grain structure as connected to
compression, drying shrinkage, clay memory, and other clay phenomena I have
been observing throughout my career in clay. Every behavior of clay in
forming and drying supports these theories. I have no reason to question or
dispute these theories, so there is no reason for me to prove anything. If
someone else chooses to disbelieve these theories, it is up to them to
gather evidence to disprove them.
Best wishes -
- Vince

Tom at Hutchtel.net on sat 29 oct 05

>>Subject: Re: S-cracks...is clay actually compressed? Oh yah!
>> are the most applicable and enduring. There is nothing absolute about
>> conclusions extrapolated from an electronmicrograph. The scientific
>> method
>> is often severely flawed.


So why isn't one of our professors, with access to all a university's
resources and student labor, taking this on in some format? And if the art
dept won't do it, why not the minerals/geology/engineering/mining dept in
conjunction with art?

Inquiring minds want to know!
Tom

Chuck Wagoner on sat 29 oct 05

Some mechanics are not very good drivers.

I do a lot of work on computer hardware, but don' ask me to help with
M.S.Word.

My brother works at NASA, but he can't hang a picture straight.

I love the week-end after Covered Bridge Festival, I'm raking my yard
and playing with my daughter.

Does anyone have a good cone 6 gun metal glaze? I used to have one that
was colored with iron and not copper, but I can't find it. Maybe next
week end I'll get some of this stuff on my desk organized.

Beautiful Sunny Day.....ahhhhhh,

Potter Wagoner in Rockville, IN.

skiasonaranthropos@FSMAIL.NET on tue 1 nov 05

Hi Tom,

=93... why isn't one of our professors, with access to all a university's
resources and student labor, taking this on in some format?=94 The answer is=

possibly that there=92s no need; the phenomenon has long been recognised and=

studied, and for craft potters a brief synopsis can be found in the
excellent book Ceramic faults and their remedies by Harry Fraser published
by A & C Black in 1986

Regards,
Antony