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nceca (clay aging for pamela)

updated sat 31 mar 07

 

stephani stephenson on tue 20 mar 07


Pamela
oh dear , you are right, i only left out one of the
more important words of the sentence!!!!!...but as
wayne said..yes the word was "improve."..that aging
clay (except the first 48 hours)did pretty much
nothing to improve the actual plasticity.

now ,i am paraphrasing from memory and without my
notes here, always dangerous... but i heard Dr. Carty
stress the importance of proper mixing...clumping of
ingredients such as felspars always a problem, and
that proper mixing is key..... so the first 48 hours
would likely be enough for proper slaking of
ingredients.....and that was more important than any
notion of aging... and yes i think he left open the
question the question of biological activity, ph
affecting the handling....
also an interesting note was the amount of water in
clay really affect how it feels in out hands ... he
acknowledged that we all have a preference in how a
clay handles how it feels, how it works ideally for
our own personal forming methods , our own
preferences..... and so we may judge whether a clay is
'good ' or not , by the feel...but that the actual
difference in the water content is quite small,
whether you prefer a stiff clay or a soft clay, the
difference in water content is about 1-3%, someone
chime in here if i am wrong....
, so the water variation in our preferences is still a
small part of the total water content....

the other number which comes to mind is the assertion
that a crazed glaze weakens the body by...what was it
, about 60%?
just ask jon singer!!!!!

the other 2 presenters on that panel were also great.
Stephani



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Vince Pitelka on wed 21 mar 07


Stephani Stephenson wrote:
> oh dear , you are right, i only left out one of the
> more important words of the sentence!!!!!...but as
> wayne said..yes the word was "improve."..that aging
> clay (except the first 48 hours)did pretty much
> nothing to improve the actual plasticity.

Dear Stephani -
As you have no doubt noticed, I do that all the time - leave out important
words, and then I have to post another message to say what I REALLY meant to
say.

Regarding the statements about aging, I didn't see the panel on claybodies
at NCECA, so I don't know what evidence they presented to support that
statement. I agree that several days should be enough to wet all the
particles, and that the nature of initial mixing is critical, but if they
really made the statement as you quote above, they must be using a creative
definition of "actual plasticity." The byproduct of organic activity is
acidic, and it flocculates the clay, improving what I would think of as
"actual plasticity." The organic activity also produces a lubricating
effect that improves plasticity, and it also means that the clay needs less
water for throwing, and is less likely to absorb water during throwing.
There are a lot of things working together in well-aged clay that improve
plasticity and performance.

I would agree that once you get beyond the first 48 hours or so after mixing
clay, there is a period of several months when there is no significant
improvement in plasticity. I don't know all the things that affect the
growth of organic activity in the clay, but when clay is beyond three or
four months old, you can smell it in the clay. My students have tried
"seeding" that organic activity with all sorts of additions, and that tends
to produce very smelly, unuseable clay for the first month or two, but after
that the organic activity really accelerates and the offensive odor just
turns into a generic earthy smell that means well-aged clay.

At the Craft Center we mix all of our own stock claybodies, and I use those
for my class demos. We date each batch, so we know how old they are. After
thirteen years of using these clays, I can tell the difference between aged
clay and new clay. I'm agreeing that after the first 48 hours there isn't
much change during the next few months, but no one is going to convince me
that aging the clay doesn't significantly improve plasticity.

Sometimes people get an idea about some accepted concept being a "myth," and
they can get pretty creative in tweaking the evidence to support their
premise. I'm not saying that is what happened here, but I am looking
forward to reading about the claybody presentation in the NCECA journal.
- 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/

WJ Seidl on wed 21 mar 07


Stephani:
Your memory is much better than mine, dear. Yes, Dr. Carty did stress the
importance of proper mixing. The only method of any "real value" it seems
was to turn the ingredients into a slurry and go from there. The electron
microscope slides in his presentation supported that. Changed my view
toward mixing, for sure. Turning it all into "soup" first is the key to
proper mixing and even distribution of ingredients throughout the mix (for
those of us mixing our own bodies).

And again, yes! Using a glaze with an improper fit reduces the strength of
the body on the order of something like 60% (it's a real b*tch getting old,
can't remember anything) because of the stresses placed on the form by the
glaze. He proved that with clay bars he extruded and fired, some with NO
glaze, and others with a poorly fitting glaze. Just amazing to see it in
practice. Jon was up on the stage in a flash to break the bars IIRC.

I hope they put that onto a DVD or into the book for the year. It was
definitely information that we needed.

Best,
Wayne

-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of stephani
stephenson
Sent: Tuesday, March 20, 2007 10:32 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: NCECA (clay aging for Pamela)

Pamela
oh dear , you are right, i only left out one of the
more important words of the sentence!!!!!...but as
wayne said..yes the word was "improve."..that aging
clay (except the first 48 hours)did pretty much
nothing to improve the actual plasticity.

now ,i am paraphrasing from memory and without my
notes here, always dangerous... but i heard Dr. Carty
stress the importance of proper mixing...clumping of
ingredients such as felspars always a problem, and
that proper mixing is key..... so the first 48 hours
would likely be enough for proper slaking of
ingredients.....and that was more important than any
notion of aging... and yes i think he left open the
question the question of biological activity, ph
affecting the handling....
also an interesting note was the amount of water in
clay really affect how it feels in out hands ... he
acknowledged that we all have a preference in how a
clay handles how it feels, how it works ideally for
our own personal forming methods , our own
preferences..... and so we may judge whether a clay is
'good ' or not , by the feel...but that the actual
difference in the water content is quite small,
whether you prefer a stiff clay or a soft clay, the
difference in water content is about 1-3%, someone
chime in here if i am wrong....
, so the water variation in our preferences is still a
small part of the total water content....

the other number which comes to mind is the assertion
that a crazed glaze weakens the body by...what was it
, about 60%?
just ask jon singer!!!!!

the other 2 presenters on that panel were also great.
Stephani



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Vince Pitelka on thu 22 mar 07


Wayne Seidl wrote:
> However, I do believe we're all on the same page here, we're not really
> disagreeing.
> Best,
> Wayne Seidl

I'm sure you are correct, Wayne. I have nothing against science. I was
raised by two emminent scientists. I do think that occasionally scientists
can develop their pet theories contrary to observable reality, but I
certainly would not pre-judge Dr. Carty's assertions before thoroughly
reading the presentation whenever it comes out in the NCECA journal. Our
beloved Stephani Stephenson originally stated it as if Dr. Carty had
declared that the idea that aging improves plasticity was a myth. That's
what I was reacting to.

I really like what Richard Aerni said in his post tonight: "You can beat a
potter over the head with a science book, but if the potter's hands tell
him/her that something is true, then it is true, no matter what science
says." There is another beloved member of this list who ocasionally tries
to beat me over the head with science books with no success at all, and it
frustrates the hell out of him. I can only go by what I observe and
experience, and I will believe that before I believe contradicting science
every time.

I am looking forward to receiving the NCECA journal. I hope they get it out
in a timely fashion.
- 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/

Richard Aerni on thu 22 mar 07


I won't quote all of Vince's excellent reply about increasing plasticity in
aged clay. It was well written and made a lot of sense. You can beat a
potter over the head with a science book, but if the potter's hands tell
him/her that something is true, then it is true, no matter what science says.
When I was beginning to throw, we mixed all our own clay. We each set aside
a bag of clay to age for handles. I remember quite clearly that those older
bags of clay were considerably more plastic than the more recently mixed
batches that went onto the wheel.
So, we can argue all we want to about increasing plasticity, but I will
wager than none of us has the laboratory at hand that will prove or disprove
any thesis on the matter. What we have is the evidence at hand, so to
speak, and that is what I base my opinion on.
Best,
Richard Aerni
Rochester, NY

Pamela Regentin on thu 22 mar 07


<<<His pictures in the presentation, clearly showing clumping of silica feldspar bore out his contention that proper mixing does indeed play a
significant role in plasticity; but more importantly, in the
homogeneity of the clay body one is making.
I don't know what criteria he assigned to his definition of plasticity,
and don't think he addressed that. >>>>
This statement makes more sense to me regarding what the presentation must have been simply because I don't see how looking at microscopic slides of the clay could tell what amount of plasticity it had. The homogenization of the clay, yes, but how could the plasticity be shown?

Pam


Richard Aerni wrote: I won't quote all of Vince's excellent reply about increasing plasticity in
aged clay. It was well written and made a lot of sense. You can beat a
potter over the head with a science book, but if the potter's hands tell
him/her that something is true, then it is true, no matter what science says.
When I was beginning to throw, we mixed all our own clay. We each set aside
a bag of clay to age for handles. I remember quite clearly that those older
bags of clay were considerably more plastic than the more recently mixed
batches that went onto the wheel.
So, we can argue all we want to about increasing plasticity, but I will
wager than none of us has the laboratory at hand that will prove or disprove
any thesis on the matter. What we have is the evidence at hand, so to
speak, and that is what I base my opinion on.
Best,
Richard Aerni
Rochester, NY

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Lee Love on thu 22 mar 07


On 3/22/07, WJ Seidl wrote:
> Stephani:
> Your memory is much better than mine, dear. Yes, Dr. Carty did stress the
> importance of proper mixing.

Did Dr. Carty only look at refined, industrial clay, or did he also
look at potter specific natural clay? You say that he says "mixing"
is important. But mixing isn't a factor in natural, non-air floated,
unrefined clays. The mix is "as is" right out of the ground, except
for screening out of large stones and organic material. There are
few organics in commercially mixed clays, so they have little
advantage in aging.

Got some great photos of the clay preparation machinery at
the Clay cooperative today. The machinery puts you in mind of the
19th century. Will put up photos soon.
--
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

WJ Seidl on thu 22 mar 07


Vince:
I'm usually one of the first to disagree with anyone, just for the sake of
playing devil's advocate . I also know that most profs put their pants
on one leg at a time, as do I (only the very talented can jump into theirs
and hit the ground running...I don't hang with that crowd) so a lot of what
comes out of "learned" mouths can be discounted. We've had our
disagreements, after all .
However, I don't remember (forgive me, my memory is not what it should be)
that Prof. Carty was addressing the long-term storage of clay. Based on
what you've said below, what Mel and others have said (archives) and my own
(limited) personal experience, I think that the point Carty was making is
still valid. He was addressing the plasticity generated by proper mixing
through mixing to a slurry, rather than wetting all the ingredients and
throwing them into a pugmill (for example).
I think he pointed more toward homogeneity.
His pictures in the presentation, clearly showing clumping of silica and
feldspar bore out his contention that proper mixing does indeed play a
significant role in plasticity; but more importantly, in the homogeneity of
the clay body one is making.
I don't know what criteria he assigned to his definition of plasticity, and
don't think he addressed that. I simply can't remember.
However, I do believe we're all on the same page here, we're not really
disagreeing.
Best,
Wayne Seidl

-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Vince Pitelka
Sent: Wednesday, March 21, 2007 11:12 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: NCECA (clay aging for Pamela)

Stephani Stephenson wrote:
> oh dear , you are right, i only left out one of the
> more important words of the sentence!!!!!...but as
> wayne said..yes the word was "improve."..that aging
> clay (except the first 48 hours)did pretty much
> nothing to improve the actual plasticity.

Dear Stephani -
As you have no doubt noticed, I do that all the time - leave out important
words, and then I have to post another message to say what I REALLY meant to
say.

Regarding the statements about aging, I didn't see the panel on claybodies
at NCECA, so I don't know what evidence they presented to support that
statement. I agree that several days should be enough to wet all the
particles, and that the nature of initial mixing is critical, but if they
really made the statement as you quote above, they must be using a creative
definition of "actual plasticity." The byproduct of organic activity is
acidic, and it flocculates the clay, improving what I would think of as
"actual plasticity." The organic activity also produces a lubricating
effect that improves plasticity, and it also means that the clay needs less
water for throwing, and is less likely to absorb water during throwing.
There are a lot of things working together in well-aged clay that improve
plasticity and performance.

I would agree that once you get beyond the first 48 hours or so after mixing
clay, there is a period of several months when there is no significant
improvement in plasticity. I don't know all the things that affect the
growth of organic activity in the clay, but when clay is beyond three or
four months old, you can smell it in the clay. My students have tried
"seeding" that organic activity with all sorts of additions, and that tends
to produce very smelly, unuseable clay for the first month or two, but after
that the organic activity really accelerates and the offensive odor just
turns into a generic earthy smell that means well-aged clay.

At the Craft Center we mix all of our own stock claybodies, and I use those
for my class demos. We date each batch, so we know how old they are. After
thirteen years of using these clays, I can tell the difference between aged
clay and new clay. I'm agreeing that after the first 48 hours there isn't
much change during the next few months, but no one is going to convince me
that aging the clay doesn't significantly improve plasticity.

Sometimes people get an idea about some accepted concept being a "myth," and
they can get pretty creative in tweaking the evidence to support their
premise. I'm not saying that is what happened here, but I am looking
forward to reading about the claybody presentation in the NCECA journal.
- 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/

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melpots@pclink.com.

Dannon Rhudy on thu 22 mar 07


I rather hate to chime in with "I think so too", but
Richard is quite right. However/whatever happens
in clay that "sits", it becomes a great deal more
plastic. I always have saved clay for "handling"
from each batch made or bought. Had my students
do the same. Something happens that makes it
more easily manipulated. My hands, like Richard's,
tell me so. I'm amenable to any explanation one way
or the other, any descriptive term, any ideas on the
mixing etc - but I need plastic clay for good handles,
and some other functions - I "age" it to get it. Whatever
happens, I'm all for it.

regards

Dannon Rhudy


> You can beat a
> potter over the head with a science book, but if the potter's hands tell
> him/her that something is true, then it is true, no matter what science
says.
> When I was beginning to throw, we mixed all our own clay. We each set
aside
> a bag of clay to age for handles. I remember quite clearly that those
older
> bags of clay were considerably more plastic than the more recently mixed
> batches that went onto the wheel.

Kathy McDonald on thu 22 mar 07


II only know what my hands tell me
and I had to go to the studio to see
if my feelings about new and old clay could
be validated by some good old fashioned
hands on trials.

I used three types of clay, some new Laguna B mix
some new Tuckers 1080, and some of my "old" (has been
sitting about a year)
special concoction.

The special concoction is the recycled scraps of the
above clays with the addition of some dry Plainsman
porcelain clay that is slurried and left to freeze during
the winter then rewedged by hand once thawed and
dried to the proper consistency.

weighed same amounts of each ( 5 pounds)
and proceeded to throw cylinders from each.

Three pulls only...just to see how they would turn out.
Centered to same diameter.

The "old" clay pulled 2 inches higher in 3 pulls.


The "old" stuff had a real "spring" to it and behaved
wonderfully despite not having been pugged....
( I don't have a pug mill-it's been on my wish list.)


I know this is NOT scientific and I did not have
an electronic microscope. I also know that the blends
of materials may have contributed to some of the
differences,
but,,,,I feel the old clay (aged) has a quality that can be
"felt".

I'm not saying that new information and technology to
assist us is a "bad" thing...its great..but I think
we have to also factor in the experience of those
that just "know" even though their "knowledge" might
not be an exact fit with some of the new technological/
scientific
information that we have access to.
I guess in this case it's seeing is believing.

Kathy

T



-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of
WJ Seidl
Sent: Thursday, March 22, 2007 7:53 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: NCECA (clay aging for Pamela)


Vince:
I'm usually one of the first to disagree with anyone, just
for the sake of
playing devil's advocate . I also know that most profs
put their pants
on one leg at a time, as do I (only the very talented can
jump into theirs
and hit the ground running...I don't hang with that crowd)
so a lot of what
comes out of "learned" mouths can be discounted. We've had
our
disagreements, after all .
However, I don't remember (forgive me, my memory is not what
it should be)
that Prof. Carty was addressing the long-term storage of
clay. Based on
what you've said below, what Mel and others have said
(archives) and my own
(limited) personal experience, I think that the point Carty
was making is
still valid. He was addressing the plasticity generated by
proper mixing
through mixing to a slurry, rather than wetting all the
ingredients and
throwing them into a pugmill (for example).
I think he pointed more toward homogeneity.
His pictures in the presentation, clearly showing clumping
of silica and
feldspar bore out his contention that proper mixing does
indeed play a
significant role in plasticity; but more importantly, in the
homogeneity of
the clay body one is making.
I don't know what criteria he assigned to his definition of
plasticity, and
don't think he addressed that. I simply can't remember.
However, I do believe we're all on the same page here, we're
not really
disagreeing.
Best,
Wayne Seidl

-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of
Vince Pitelka
Sent: Wednesday, March 21, 2007 11:12 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: NCECA (clay aging for Pamela)

Stephani Stephenson wrote:
> oh dear , you are right, i only left out one of the
> more important words of the sentence!!!!!...but as
> wayne said..yes the word was "improve."..that aging
> clay (except the first 48 hours)did pretty much
> nothing to improve the actual plasticity.

Dear Stephani -
As you have no doubt noticed, I do that all the time - leave
out important
words, and then I have to post another message to say what I
REALLY meant to
say.

Regarding the statements about aging, I didn't see the panel
on claybodies
at NCECA, so I don't know what evidence they presented to
support that
statement. I agree that several days should be enough to
wet all the
particles, and that the nature of initial mixing is
critical, but if they
really made the statement as you quote above, they must be
using a creative
definition of "actual plasticity." The byproduct of organic
activity is
acidic, and it flocculates the clay, improving what I would
think of as
"actual plasticity." The organic activity also produces a
lubricating
effect that improves plasticity, and it also means that the
clay needs less
water for throwing, and is less likely to absorb water
during throwing.
There are a lot of things working together in well-aged clay
that improve
plasticity and performance.

I would agree that once you get beyond the first 48 hours or
so after mixing
clay, there is a period of several months when there is no
significant
improvement in plasticity. I don't know all the things that
affect the
growth of organic activity in the clay, but when clay is
beyond three or
four months old, you can smell it in the clay. My students
have tried
"seeding" that organic activity with all sorts of additions,
and that tends
to produce very smelly, unuseable clay for the first month
or two, but after
that the organic activity really accelerates and the
offensive odor just
turns into a generic earthy smell that means well-aged clay.

At the Craft Center we mix all of our own stock claybodies,
and I use those
for my class demos. We date each batch, so we know how old
they are. After
thirteen years of using these clays, I can tell the
difference between aged
clay and new clay. I'm agreeing that after the first 48
hours there isn't
much change during the next few months, but no one is going
to convince me
that aging the clay doesn't significantly improve
plasticity.

Sometimes people get an idea about some accepted concept
being a "myth," and
they can get pretty creative in tweaking the evidence to
support their
premise. I'm not saying that is what happened here, but I
am looking
forward to reading about the claybody presentation in the
NCECA journal.
- 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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Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.

____________________________________________________________
__________________
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You may look at the archives for the list or change your
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Hank Murrow on thu 22 mar 07


On Mar 22, 2007, at 8:18 AM, Kathy McDonald wrote:

> II only know what my hands tell me
>
> The "old" clay pulled 2 inches higher in 3 pulls.
>
> The "old" stuff had a real "spring" to it and behaved
> wonderfully despite not having been pugged....
> ( I don't have a pug mill-it's been on my wish list.)

So Kathy;

All you need is time.......... or if you want to do it quicker, just
mix all your clay in slurry and quietly dry it to wedging consistency
in canvas bags hung from your rafters.

Cheers, Hank
Hank Murrow
www.murrow.biz/hank

Jon Pacini on thu 22 mar 07


Greetings All---- All this talk about aging methods and Bill Carty's clay
presentation got me to thinking--- always a dangerous activity--- about a
conversation I had with Bill a few years back over a game of pool and how
plasticity/firmness related to the pH of a clay.

In watching the stock clay bodies here in the warehouse it came to my
attention that some clays get soft, some get hard and others seem to be just
fine indefinitely and that it didn't have anything to do with the amount of
water in the body. So at Bill's suggestion I tested the pH of the various
bodies.

I chose to test with litmus paper and got a lot of very loose, but
interesting info that went like this---

A clay that starts out pH neutral and remains neutral, remains the same
firmness as what it was made at, but if it has a tendency to leach it's
alkalis into solution, it will initially soften up as it sits around. Then,
if the alkalinity continues to increase, it hardens up. To the point where
it can become rock hard. What's really odd is that the clay appears very
hard outwardly, so hard that you can barely press your thumb into it. But
when the clay is manipulated a bit, it's back to being just as soft and
plastic as when it came out of the pug mill.

So---If you get a particularly soluble batch of Nephline Synite in your ^5
Porcelain for example, it will run the whole range for you if you wait long
enough. It comes out of the pug mill perfect---in a couple of days it's
turned to tooth paste and then in a couple of weeks it's hard as nails. All
on it's own. But if you beat it around a bit, it goes back to being fine
again.

Well then, how to fix it from getting out of whack in the first place---
Vinegar has always been a favorite addition to clays of potters who profess
its attributes in adding plasticity to clay. It also happens to be a 5%
acid solution, so I ran some tests adding vinegar to clays that tended to
vary in firmness due to alkalinity. And not so amazingly, it does indeed
counteract the alkalinity and brings the clays back to pH neutral and the
clays remain a somewhat consistant firmness. But only for as long as the
amount of vinegar can over whelm the continued leaching of the soluble
alkalis. Once the pH is on the rise again, the clay starts reacting again.

An over abundance of vinegar didn't seem to adversely affect the clays
firmness, but man--- various molds blossom virtually overnight in vinegar
enhanced clays. I've never seen such colorful Porcelain. Fortunately it's
all organic and it seems to burn out in the kiln

I have yet to come up with exact pH levels that seem to be cutoffs for
particular reactions, I'll leave that for Dave F--if there are any. It seems
to vary from clay to clay depending on the composition and of course how
soluble any given material is at the moment.

---So my conclusion at this point is, that like so many things in ceramics,
Alkalinity or lack there of is a contributing factor to plasticity, and
vinegar does change it, but that's certainly not the only factor.

Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co

Darlene Yarnetsky-Mudcat Pottery on fri 23 mar 07


I am enjoying this thread as I am cleaning and painting the studio in
preparation for returning to clay after a 15 month absence. It has
occurred to me that my peter pugger is full of clay that has been
sitting waiting for me for at least that long and I expect it shall
be an interesting day when I get up the nerve to look inside!
(windows and doors should probably be open first, eh?) I have over
the years occasionally enjoyed some wonderful throwing clay over a
year old - I do believe there is a quite a difference!

Happy potting, happy spring!
Darlene Y.

Ivor and Olive Lewis on sat 24 mar 07


Dear Friends,
From what I have read recently and in the past, Prof W. Carty conducts =
research projects funded by industrial producers of ceramic materials.
In a recent post, Mel spoke of firing times as short as 15 mins, cold to =
cold. Think about an automated factory: Materials are delivered, stored, =
batched, mixed, transported, weighed, pre-formed, shaped, have handles =
stuck to them, are rapidly dried, rapidly fired, cooled with a period of =
stasis to allow for a smooth transition through quartz inversions, =
packed and loaded to be delivered to customers for decoration. The =
product; plain cylindrical bisque porcelain mugs made on an automated =
line at the rate of several thousands per day, all without being touched =
by Human Hands. Such places are manned by a teams of engineers who work =
a three shift system. They are there to check dials, press buttons, =
twist switches and scan charts.
Given such a vast capital expenditure on automation and control systems =
and the need to give a return to shareholders would it be prudent to use =
clay that had to stand around for several weeks before it could be used. =
I do not know of the context in which that paper was presented but it is =
the research done by such as Prof. W. Carty and their graduate students =
that makes such things possible. If their insights can assist us we =
should exploit their findings.
I would like to read such papers and regret that circumstance do not =
permit me to attend such conferences.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

Lynne and Bruce Girrell on sat 24 mar 07


Kathy McDonald wrote:

>I only know what my hands tell me
>and I had to go to the studio to see
>if my feelings about new and old clay could
>be validated by some good old fashioned
>hands on trials.

What you experienced is valid. But what you did is completely outside of
what Dr. Carty was talking about. So, yes, your results will be different.

Dr. Carty stressed proper mixing as being the key. And there is no amount of
wedging, pugging or anything else that will achieve proper mixing other than
high speed blunging in the fluid state. Until you start with those
conditions, there is nothing to compare.

Also a key component of the presentation was the concept of "green packing
density". Imagine filling a room with basketballs and softballs. Fill the
room halfway with basket balls and then pour in the softballs. If you were
able to cut open the room, you would see that there is a lot of space
remaining between the balls. You could fit a lot more balls in the room if
you threw in some basketballs, some softballs, some basketballs, some
softballs, and so on. The softballs would fill in a lot of the spaces
between the basketballs and you could get more total balls in the room; you
would achieve a higher density in the room.

Now add squash balls and marbles to the mix. If you mix the the basketballs,
softballs, squash balls and marbles together well as you fill the room you
will get a very dense packing of the balls.

Porcelain is sort of like the basketballs and softballs. Big quartz and
feldspar grains with smaller kaolin particles. Good mixing achieves the best
packing of these particles. Stonewares are more like the basketball,
softball, squash ball and marble mix. Quartz, feldspar, kaolin and a range
of much smaller ball clays. There is a significantly greater range of
particle size and the packing density (when properly mixed!) will be much
better.

Workability of a clay can be related to its packing density. From the
analogy above, we would expect stonewares to have better workability than
porcelain and, in fact, that's what we observe. And we also observe an
improvemnet in the workability of porcelain with the addition of ball clay
or bentonite.

While the green packing density will improve for any clay with proper mixing
it will also improve by starting with a better selection of materials.

To be complete I should mention that workability starts to drop again as
packing density increases beyond a certain point. Imagine a perfect packing
of 100%. The volume would be solid. It would be impossible for the particles
to move relative to one another.

Possible effects of aging were not discussed by the panel. But we might make
a few guesses as to why aging might benefit a poorly mixed clay body. More
time would allow water to better infiltrate the mixture. Better wetting
would provide better workability by efffecively making some larger particles
into a few smaller ones. Over a longer time period, bacterial action could
also break down some of the larger particles into smaller ones.

So, what Dr. Carty said is not inconsistent with our collective experience
with aged clays, as few of us are working with properly mixed clays. Even
wet process clays from a commercial supplier will likely be mixed only for a
short time. As we all have heard, time is money. As soon as the clay mixture
can be pressed, there is no economical reason to continue mixing it and good
economical reason not to. Still, we may expect that any wet process clay
body would benefit less from aging than the same body prepared by dry
mixing.

Bruce Girrell
still exiled from Clayart, though now at least receiving a small percentage
of Clayart messages

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Ron Roy on sat 24 mar 07


> There are
>few organics in commercially mixed clays, so they have little
>advantage in aging.


Nothing could be further from the truth than the above statement. All the
clays we use have plenty of organic material for bacteria to work on.

Clays mixed in North America will begin to age as soon as they are mixed.

Clays do not age in the same way nor at the same speed by the way - and it
does not always result in better workability.

When alkalies are released deflocculation can be the result and this will
affect workability in a negative way

Workability is improved when bacterial action results in higher acidity.

There are ways to help the process along. Having the clay in a workable
consistency (throwable) is important, in a warm place(as opposed to cold -
bacteria are more active in warm places) and - if a little old (aged) clay
is mixed in - it will help the process go a lot faster.

If thats still not fast enough - do all the above and do a little wedging
once a week - it will feel like magic. Repugging will do the same.

RR





Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0

Bonnie Staffel on sat 24 mar 07


Clayarters, It has always been my belief that it was the rotting of the
organic materials in the clay that created the slime and mold that made the
clay plastic. I was putting away clay for handles 50 years ago when I was
early in my career in clay. Seems to me to be a simple answer. I also add
rotting clay slurry to mix with new clay out of the bag when running it
through the pug mill. Sure does increase the plasticity, as without it the
extruded pugs would crack when bent. Of course, my chemistry degree is of
the armchair variety

Bonnie Staffel

http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Beginning Processes
Charter Member Potters Council

Vince Pitelka on sat 24 mar 07


Ivor Lewis wrote:
"I would like to read such papers and regret that circumstance do not permit
me to attend such conferences."

We all regret that circumstances do not permit you to attend such
conferences. Perhaps some situation will allow you to attend NCECA at some
point in the future, and so many people will be so glad to meet you
face-to-face after all these years.
- 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/

Leigh Whitaker on sat 24 mar 07


In a message dated 3/24/2007 8:03:11 P.M. Eastern Daylight Time,
bstaffel@CHARTERMI.NET writes:

Clayarters, It has always been my belief that it was the rotting of the
organic materials in the clay that created the slime and mold that made the
clay plastic. I was putting away clay for handles 50 years ago when I was
early in my career in clay. Seems to me to be a simple answer. I also add
rotting clay slurry to mix with new clay out of the bag when running it
through the pug mill. Sure does increase the plasticity, as without it the
extruded pugs would crack when bent. Of course, my chemistry degree is of
the armchair variety

Bonnie Staffel


This is pretty interesting to me. I used to have a job in which I analyzed
the 'bugs' that were in soil, environmental, and biological samples. We
would take the sample, often dirt, and whack it around with some glass beads to
break the cell walls of the microorganisms. We would then amplify a piece of
DNA that coded for a well conserved but variable gene, so it would amplify
this gene fragment from whatever microorganisms were present in the sample.
Then we'd run these amplified fragments on a gradiated denaturing gel which
would separate DNA strands that were different in even one base pair. We could
then isolate the bands and sequence the DNA, run the sequence through a
database and identify the organism it came from. I got some samples one time that
were from some sort of treatment facility where the pH of the material was
around the 1.0 range (very acidic). They were screaming hot with one
particular strain of bacteria that liked low pH. It was really neat.

So that was kind of rambling, but it makes me wonder if there are particular
bugs that make the clay more plastic, and if they could be identified. Or
if there are particular bugs that like to grow in clay slurries and having
more of them present (plus whatever nutrient source they like to eat) would
increase their waste products and make the clay more plastic. That would be a
neat research project.

Leigh



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Sam or Mary Yancy on sat 24 mar 07


Sort of mixins a "starter" when making sour-dough bread??? sam in Daly City - the french bread capitol of the world........(some of the starter dough goes back to the 1850's......

Bonnie Staffel wrote: Clayarters, It has always been my belief that it was the rotting of the
organic materials in the clay that created the slime and mold that made the
clay plastic. I was putting away clay for handles 50 years ago when I was
early in my career in clay. Seems to me to be a simple answer. I also add
rotting clay slurry to mix with new clay out of the bag when running it
through the pug mill. Sure does increase the plasticity, as without it the
extruded pugs would crack when bent. Of course, my chemistry degree is of
the armchair variety

Bonnie Staffel

http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Beginning Processes
Charter Member Potters Council

______________________________________________________________________________
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.

Vince Pitelka on sat 24 mar 07


Bruce Girrell wrote:
> Possible effects of aging were not discussed by the panel. But we might
> make
> a few guesses as to why aging might benefit a poorly mixed clay body. More
> time would allow water to better infiltrate the mixture. Better wetting
> would provide better workability by efffecively making some larger
> particles
> into a few smaller ones. Over a longer time period, bacterial action could
> also break down some of the larger particles into smaller ones.

Bruce -
It is so positively WIERD to hear all of this discussion overlooking the
primary effects of aging. You don't mention the most important ones, and I
wonder why. I've already mentioned them in several messages so I won't
repeat them here, but it is a sure thing that the effects of aging are at
least as important as proper mixing and "green packing density" in preparing
a truly superior plastic claybody. I have this impression that there are a
lot of highly experienced potters out there hearing about this NCECA panel
on claybodies and saying "Where the hell are these people getting their
information???"

Granted that aging a claybody containing neph sy or soda spar can have an
opposite effect. Otherwise, aging is nothing but good.
- 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/

Tom at Hutchtel.net on sun 25 mar 07


I'm kind of surprised that there has been no discussion of additives (other
than floc/defloc) for clay. A couple of years ago Tom Coleman gave a
workshop here (thanks to Mr Ferguson and Ernest Miller) and the porcelain he
wqas using was a combination that was, he said, less than 50% clay but with
an additive. While he didn't disclose the additive, he said it cost over
$100 per gallon, took less than a few tablespoons per ton and was a fairly
common food additive. He said he, along with the folks at Aardvark Clay had
developed it.

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


> "Regarding the improved plasticity of aged clay: Could you estimate a
> quantification of the improvement? For example two vessels thrown
> from two different clays...one well made, but not aged and the other
> well made and aged: Could you estimate the difference in height or
> volume of the resulting vessel?

John Jensen on sun 25 mar 07


Vince;
Why would I ask you if you might be able to quantify the improvement
in the clay which is a result of aging? On the off chance that you
might have an answer, I guess. Though I might be somewhat of an
experienced studio potter, I still have a hard time sorting things
out. I can't always nail down why some things work better for me than
others, even in areas where I have plenty of experience. So I thought
maybe you'd be able to say something like, "at least ten percent more
height for a given cylinder." Or "It seems like the walls of my
vessels are a good third thinner when I use aged clay." If you had
been able to do that, it would have given me something to compare my
own experience to. Now that I think of it, to quantify things seems
to be the basis of science. I guess saying A>B is a form of
quantification, but I was hoping for something a bit more specific.
Anyway, best wishes...no big deal.


John Jensen, Homewood Pottery
homewoodpottery.com
johnjensen@homewoodpottery.com

> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Vince
> Pitelka
> Sent: Sunday, March 25, 2007 7:58 PM
> To: CLAYART@LSV.CERAMICS.ORG
> John -
> Like so many things in art and craft, there's no way I know of to
> quantify
> this. ave explained in several preverious posts.
> It
> never occured to me to try and quantify the improvement, or to even
> WANT to
> quantify it. It is something every experienced studio potter knows,
> especially those who work on the wheel. I am sure that you have the
> experience to tell the difference, so I am curious as to why you are
> asking
> me?
> - Vince
>=20
> 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/

John Jensen on sun 25 mar 07


Vince;
Regarding the improved plasticity of aged clay: Could you estimate a
quantification of the improvement? For example two vessels thrown
from two different clays...one well made, but not aged and the other
well made and aged: Could you estimate the difference in height or
volume of the resulting vessel? I ask you, not to challenge your
assertions; but because you seem so definite about them, I hope you
may have an answer.
I'm glad you finally made it back to NCECA after all these years,
sorry I missed you. Maybe in New Orleans.

John Jensen, Homewood Pottery
homewoodpottery.com
johnjensen@homewoodpottery.com

> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Vince
> Pitelka
> Sent: Saturday, March 24, 2007 8:34 PM
> To: CLAYART@LSV.CERAMICS.ORG
but it is a sure thing that the effects of aging
> are at
> least as important as proper mixing and "green packing density" in
> preparing
> a truly superior plastic claybody. Otherwise, aging is nothing but
good.
> - Vince
>=20
> 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/

Vince Pitelka on sun 25 mar 07


John Jensen wrote:
"Regarding the improved plasticity of aged clay: Could you estimate a
quantification of the improvement? For example two vessels thrown
from two different clays...one well made, but not aged and the other
well made and aged: Could you estimate the difference in height or
volume of the resulting vessel? I ask you, not to challenge your
assertions; but because you seem so definite about them, I hope you
may have an answer."

John -
Like so many things in art and craft, there's no way I know of to quantify
this. You can pull taller vessels with soft clay if it is aged long enough
to have a lot of organic activity present. It improves the clay in a number
of different ways, as I have explained in several preverious posts. It
never occured to me to try and quantify the improvement, or to even WANT to
quantify it. It is something every experienced studio potter knows,
especially those who work on the wheel. I am sure that you have the
experience to tell the difference, so I am curious as to why you are asking
me?
- 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/

John Jensen on mon 26 mar 07


Vince;
For that matter, I know that clay which has gone through the recycling
process of pugging and wedging is a lot more satisfying to throw with
as well. If I had to quantify this satisfying experience, I'd say I
would go from a failure rate (in throwing) of 2% (ie: screwing up a
couple of pots in a hundred) to a failure rate of ,5% (i.e.: screwing
up one in two hundred) For a grand result of a 400% improvement. Wow!
On the other hand, I could compare speed and say: go from 24 to 36
pots per hour for an improvement of %50.
I guess this quantification game is pretty dicey, at that; even when
one is making up the data.
Best wishes.

John Jensen, Homewood Pottery
homewoodpottery.com
johnjensen@homewoodpottery.com

> -----Original Message--EDITED

---
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Vince
> Pitelka
> Sent: Monday, March 26, 2007 7:01 PM
I guess I tend to take a more intuitive
> approach to
> most things. So, from long experience I know that well-aged clay is
> much
> more satisfying to throw for a variety of reasons, but I can't
> quantify any
> one of them.
I know that
> the clay
> that had been sitting around for four to six months was much more
> satisfying
> to throw than the stuff that just arrived.
> - Vince
>=20
> 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/
>=20
> ____________________________________________________________________
> __________
> Send postings to clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list or change your
> subscription
> settings from http://www.ceramics.org/clayart/
>=20
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.

Lee Love on mon 26 mar 07


On 3/24/07, Lynne and Bruce Girrell wrote:

> Dr. Carty stressed proper mixing as being the key. And there is no amount of
> wedging, pugging or anything else that will achieve proper mixing other than
> high speed blunging in the fluid state. Until you start with those
> conditions, there is nothing to compare.

This is another reason while potter specific clay is better than
industrial mixed clay. Because the clay comes out of the ground
whole and it is only blundged and screened, it is never in an
"unmixed" state.


--
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

Leigh Whitaker on mon 26 mar 07


In a message dated 3/26/2007 6:40:35 A.M. Eastern Daylight Time,
togeika@CLAYCRAFT.ORG writes:

This is another reason while potter specific clay is better than
industrial mixed clay. Because the clay comes out of the ground
whole and it is only blundged and screened, it is never in an
"unmixed" state.


Can someone please tell me what blundged means?

Thanks,
Leigh



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Vince Pitelka on mon 26 mar 07


John Jensen wrote:
"Now that I think of it, to quantify things seems
to be the basis of science. I guess saying A>B is a form of
quantification, but I was hoping for something a bit more specific.
Anyway, best wishes...no big deal."

John -
I agree, and having turned away from being a professional scientist like my
parents fairly early on, I guess I tend to take a more intuitive approach to
most things. So, from long experience I know that well-aged clay is much
more satisfying to throw for a variety of reasons, but I can't quantify any
one of them.

When I was doing pots full-time in California I purchased all of my clay
from Westwood, usually around 5 tons at a time. When I got down to where I
had about half an order left, I'd place another order. I know that the clay
that had been sitting around for four to six months was much more satisfying
to throw than the stuff that just arrived.
- 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/

Carty, William M on mon 26 mar 07


To whom it may concern:

=20
I gave a presentation at NCECA in Louisville on clay and bodies. (Yes,
I am the infamous Dr. Carty, although I never refer to myself that way.
I am "Bill" to my friends and all the artists I interact with.) I also
made comments on aging clays. I believe on the ClayArt discussion site
however, my comments have been taken out of context. (I can't tell from
the discussion if Phil was present, but he seems rather angry -- and I
checked, I am using the word myth or mythology correctly according to
Merriam-Webster's Collegiate Dictionary. I can elaborate if necessary.)

=20
Also, however, I believe it is really important for all of you to
realize that the talks were not about aging! The question about aging
came up in the short question and answer period at the end of talk and
was just briefly addressed. If this is really of interest, and it may
be, I would be happy to address aging at some future date. David Pier
talked about things of importance to artists with regards to clay
bodies. Matt addressed the importance of particle size on workability
of clay bodies -- and yes, he had a fair number of great electron
microscope images of clays and feldspars. And I talked about how the
bodies fire and also touched, briefly, on the importance of mixing from
observations on slumping. We did not address aging in our talks so you
will likely be disappointed when the NCECA publication comes out.=20
=20
While I am not an artist (nor technically a scientist -- my background
is ceramic engineering), I have worked with artists for roughly 20 years
answering, to the best of my ability, questions regarding ceramics.
Over time, too, my answers have sometimes changed based on observations.
In all cases, I weigh the question and decide how to best answer the
question. I have never disputed that artists may be able to feel
differences that we are unable to measure, but my observations, and
particularly those regarding aging and clay, have typically been tested
and evaluated by artists. To all who know me, know that I am hands-on
and eagerly enter into discussion on the way that things behave --
particularly clays. =20
=20
Artists and industrial types pay a lot of attention to aging. As a
result of both interactions with industry and with artists, we have
evaluated aging from an experimental perspective. For this discussion,
I believe it is necessary to define aging as change in behavior until
steady-state is achieved. In other words, the clay may change with time
until it stops changing. We (my research group and the Whiteware
Research Center) have always been interested in measuring behavior, but
more importantly, in mechanisms. We are much more interested in WHY
something happens, rather than WHAT happens. From the perspective of
why, we can help to understand better how to control the behavior or to
compensate for changes in behavior. That seems to be something that
artists find valuable. =20
=20

The common misperception (myth?) is that clay "ages" due to bacteria
growth. I believe this was likely true 75 years ago or longer, but not
for modern clay. While articles on aging have all but disappeared from
recent literature (at least for industrial clay discussions), they were
somewhat common up to the 1940s. I recall several articles specifically
that grew bacteria in clay during the 1920s. The problem, however, is
that it was not possible to explain why in some cases the clay would
become easier to work and sometimes harder. The change in clay
workability did not seem to be connected to bacteria growth based on the
discussions in these articles, and frankly, the workability discussions
were a bit vague. But that is not surprising, however, because the goal
of article was to address bacteria growth. =20
=20
The mythology associated with ancient Chinese potters is that they would
bury their clay in the ground for their grandchildren to allow the clay
to age and have the best workability. This may have been true at one
point, perhaps several hundred years ago, but does not seem to be the
case any longer. Clay is produced in China much the same way as it is
produced here in the U.S.: raw materials are mined, ground, mixed with
water, worked into a plastic mass, then used. The mass production
system does not really have mechanisms that allow for clay to be stored
for months, let alone years, before use. I believe that is also true of
artists in the U.S. Clay is purchased for use. Few artists have the
storage capacity to keep enough clay to last for years of work. Typical
clay storage is less than one year (based on a limited sampling of
artists I know that I asked, but it make sense). =20
=20
Clay does age, but this aging, based on our observations (and a large
amount of research and experimentation) is due to raw material
dissolution and an increase in dissolved salts or ions. In a well mixed
clay, this process is complete within a day or two at the most. The
clay does not continue to dissolve with time due to the achievement of a
sort of equilibrium or steady-state in the water chemistry. Of course,
if the clay is poorly mixed, this process may take considerably longer,
but the process is still likely done in less than a week. =20
=20
Furthermore, and perhaps most importantly, if the clay is obtained from
a commercial vendor, and from my experience a vast majority of the clay
used by artists comes from commercial clay suppliers, it has a limited
window for aging. Whether the clay is purchased as a raw material from
a supplier (such as Zemex or Unimin, etc.) or as a mixed body (such as
from Laguna, or Trinity, etc.) then the clay is not likely be a good
candidate medium for bacteria growth. There are two reasons, but one is
sufficient: The clay has been mixed with tap water. Tab water
typically contains, if nothing else, chlorine -- and chlorine kills
bacteria. It is as simple as that. I have also been told that
commercial clays contain an anti-bacterial agent, but have not verified
this. =20

=20
The second reason is a practical one. A box clay, bought from a
supplier or from a distribution retailer is of indefinite age, but it is
quite unlikely that the clay will have set, in the box, for less than
one week when the artist receives it. The clay body cannot be
reasonably batched, mixed, extruded, boxed, and shipped in less than one
week. It is likely considerably longer than that for the simple reason
that these companies produce more than one or two bodies. Twenty bodies
is more likely the case. It costs money to change the recipe, with mill
clean-out, changing recipes, etc. The clay suppliers make as much clay
as the market will bear at one time -- typically at least a few tons of
clay. This clay then sits in a warehouse waiting to be shipped, or in
the distributor warehouse waiting to be bought. Therefore, I would be
surprised if the clay changes at all once in the hands of the potter or
artist. =20
=20
In industry, however, things are different. Clay is produced in-house
and it can get into the process immediately. Assuming that my argument
that it takes a day for things to equilibrate (age if you like), this
clay may appear to be different and changing in the industrial process.
In these situations, it is possible that the clay will be changing,
aging if you like, producing a non-uniform behavior with time. This
problem shows up as increased loss rates for the simple matter that
machines are unable to compensate for changes in the clay. If the clay
is allowed to set, in the plastic state, even for only a day, these
variations or changes are unnoticeable.
=20
That said, if an artist digs clay from a river bed and used the river
water to mix the clay, then yes, aging due to bacteria is quite
possible. Also, if you mix your clay using beer instead of water, that
may be similarly true. However, again, if mixed using tap water, aging
due to bacteria growth is quite unlikely. Note also though that not all
tap water is the same. If an artist moves to a new location, changes in
the water chemistry can cause changes in the workability and behavior of
the clay. =20
=20
The fact is that aging for artists should not be a great problem.
Changes that are seen could be due to several things, drying, changes in
humidity, temperature of the clay, etc. However, I don't believe that
aging is really an issue. =20
=20
Feel free to email me with questions. I will respond as quickly as I
can. =20
=20
Cheers.
=20
Bill Carty
=20
carty@alfred.edu
=20
=20
=20
=20

primalmommy on tue 27 mar 07


I am kind of excited to see the posts by the presenters. It's too bad
they seem to have been put on the defensive. Most of us were arguing
about an idea, based on a second-hand retelling of something we hadn't
witnessed, and certainly intended no disrespect to the experts/science
involved. I am also concerned that some of the more colorful citizens of
clayart-ville might seem to represent the entire list, at least to folks
unfamiliar with our weird little town.

I suspect that the missing puzzle piece is the extent to which potters
recycle clay. Many university and community art programs make clay in
large mixers, using the community slop barrel like bakers use sourdough
starter (and the stinkier, the better.) I do buy bagged clay in my own
home studio, but have big rubbermaid storage boxes stacked along an
outside wall full of years-old trimming scraps, rejected greenware, and
clay that dried out on me -- mostly reconstituted with water from my
rain barrel, and often mossy green by the time I pug and reuse it.

I think the presenters may have underestimated the number of potters,
students, teachers and guilds who use clay mixers, pug mills, plaster
sinks or old bluejean-legs to turn clay slop back into useable clay --
now full of skin cells, yeast from the air, and whatever organics drift,
fall or are sneezed into the clay.

In the EMU studio, the first batch of clay we made fall semester was
almost unuseable. By the time the classes had generated a couple of
trash cans full of splash pan dumpings, trimmings, and pots that didn't
survive critique, the clay improved immensely. The grad students soon
learned to make big batches whenever the slop buckets got particularly
ripe, and store it for as long as possible. Mine is in a wooden bin
against the wall shared by the kiln, so it's nice and warm as well. It's
almost like leaving bread dough to rise.

I don't know if there's a way to quantify all of this. It would probably
involve some kind of survey, of the sort used by ceramics mags or the
potters council, to find out how many potters own pug mills or clay
mixers... how many work in university or community studio programs or
guilds where clay is made... how many studio potters who buy bagged clay
also recycle or add something to change its workability.

Short of that, it might be best to add disclaimers: like "Bagged
commercial clays made using chlorinated water are not improved by aging
past the time required for dry materials to absorb liquid". (For all I
know, you did say that and the rest was lost in translation.)

Anyway, welcome to the list, guys, and please stick around. We have some
glaze chemistry geeks here who we learn from and argue with and value
immensely. Good science is always welcome here, as is the open exchange
of ideas -- that's the spirit of scientific inquiry.

Yours
Kelly in Ohio, a potter/writer married to a woodworking biologist, happy
with one foot in art and one in science.


http://www.primalpotter.com


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Taylor Hendrix on tue 27 mar 07


Hey you two bearded wonders,

I dig what you're saying but "satisfaction" is by some scientific
standards unquantifiable so don't even try, but you two stinkers knew
that. I think interpretation of what scientists say is what is the
dicey thing in most situations. Better to understand that science says
something rather than everything on a certain subject.

Hey, perhaps well aged clay smells comforting and that in turn makes
one feel better when throwing it. One can't help but feel good about
business when half the clay order has been thrown, right?

Anyway, I can't wait to dry out the two 5 gal buckets of slip I have
had sitting around for about a month. I have a "feeling" that that
stuff is going to be golden.

Let's get dirty,

Taylor, in Rockport TX

On 3/26/07, John Jensen wrote:
...
If I had to quantify this satisfying experience,
...

> I guess this quantification game is pretty dicey, at that; even when
> one is making up the data.
...

Kathy Forer on tue 27 mar 07


On Mar 26, 2007, at 8:01 PM, Vince Pitelka wrote:

> I know that the clay
> that had been sitting around for four to six months was much more
> satisfying
> to throw than the stuff that just arrived.

It seems to have a lot to do with density. When clay is brand new
from a bag it's kinda tight and a little slimy. Somewhat unnaturally
plastic, too dense. It needs more air and more volume so it can be
compressed by your hands or tools, not the bag. Wedging or even
slamming doesn't do it. It needs to be taken apart to some degree and
reconstituted.

If the clay is store new and time is pressing, simply sitting a
plastic bag of clay in a full bucket of water will go far toward
reconditioning the clay. If time permits, it's even better if it gets
too soft and wet and needs to be dried out.

I don't have a bathtub but keep several five gallon tubs of clay
under my wedging table (and more two gallon buckets on shelving).
Some of the clay is pretty old by now but when it's dried out and
wedged it's just the way I like it.

Kathy

--
Kathy Forer
www.foreverink.com

Matthew Katz on tue 27 mar 07


Well, Thanks for the welcome!
We are excited to be entering this forum, and we think that this is a great
place to keep the conversation going.
I should say that, you will often find that both Bill and I will answer
posts, depending on who gets to the first, but there may be some redundancy=
,
and maybe even some disagreement between us. But we work together and share
the same information and philosophy. In the end we have no agenda, we are
only interested in making ceramics the best they can be.
I'm sorry if either of us came off as defensive, but I it is hard to judge
people's tone on email. As I said we are not interested in making the
ceramics world see things our way, we are just sharing the knowledge that w=
e
have gained through years of research. We just like to get knowledge and
discussion out there, as we do every day here in Alfred. Part of that daily
exchange is working with artists, and working as artists (as I myself am).
So I would like to reiterate one point. That is there seems to be an
assumption, that me are missing something about the artistic process. Or
that we are creating this data out of whole cloth. The fact is that we know
how artists work, we know how their studios function. we know how they mix
their clay or glazes, or how they throw, sculpt, or fire. We do it ourselve=
s
every day in our own studios (except Bill, but it is really funny to watch
him try the wheel). Bill makes up for this by having lunch with John Gill
almost every day, where they discuss what we have been working on and John
tunes Bill into how things really work. So we ask that you give us the
benefit of the doubt.
As per your particular point, I think that there is a step in the process
that you might have overlooked. In your discussion of slop clay you assume
that the aging of the slop is what it made it better. I would argue that it
is in fact the slaking of the clay body that enhance the performance. For
those who did see our presentations at NCECA, you will not that the vast
majority of of conversation was about proper mixing (50%) vs aging (0.01%),
and how Slurry mixing, is by leaps and bound the best way to improve clay
performance on all fronts. The fact is that that by slaking down you clay
you are putting it in a slurry state, and aiding in throughly mixing the
clay which was not accomplished in the first place. Where as the traditiona=
l
mixing methods (Soldner and Dough Mixers) Do a poor job of properly mixing
the clay form the start. By braking the clay down and getting it mixed up
really well in a slurry, you will improve you performance dramatically.
Best,
Matt

On 3/27/07, primalmommy wrote:
>
>
>
> I am kind of excited to see the posts by the presenters. It's too bad the=
y
> seem to have been put on the defensive. Most of us were arguing about an
> idea, based on a second-hand retelling of something we hadn't witnessed, =
and
> certainly intended no disrespect to the experts/science involved. I am al=
so
> concerned that some of the more colorful citizens of clayart-ville might
> seem to represent the entire list, at least to folks unfamiliar with our
> weird little town.
>
> I suspect that the missing puzzle piece is the extent to which potters
> recycle clay. Many university and community art programs make clay in lar=
ge
> mixers, using the community slop barrel like bakers use sourdough
> starter (and the stinkier, the better.) I do buy bagged clay in my own h=
ome
> studio, but have big rubbermaid storage boxes stacked along an outside wa=
ll
> full of years-old trimming scraps, rejected greenware, and clay that drie=
d
> out on me -- mostly reconstituted with water from my rain barrel, and oft=
en
> mossy green by the time I pug and reuse it.
>
> I think the presenters may have underestimated the number of potters,
> students, teachers and guilds who use clay mixers, pug mills, plaster sin=
ks
> or old bluejean-legs to turn clay slop back into useable clay -- now full=
of
> skin cells, yeast from the air, and whatever organics drift, fall or are
> sneezed into the clay.
>
> In the EMU studio, the first batch of clay we made fall semester was
> almost unuseable. By the time the classes had generated a couple of trash
> cans full of splash pan dumpings, trimmings, and pots that didn't survive
> critique, the clay improved immensely. The grad students soon learned to
> make big batches whenever the slop buckets got particularly ripe, and sto=
re
> it for as long as possible. Mine is in a wooden bin against the wall shar=
ed
> by the kiln, so it's nice and warm as well. It's almost like leaving brea=
d
> dough to rise.
>
> I don't know if there's a way to quantify all of this. It would probably
> involve some kind of survey, of the sort used by ceramics mags or the
> potters council, to find out how many potters own pug mills or clay
> mixers... how many work in university or community studio programs or gui=
lds
> where clay is made... how many studio potters who buy bagged clay also
> recycle or add something to change its workability.
>
> Short of that, it might be best to add disclaimers: like "Bagged
> commercial clays made using chlorinated water are not improved by aging p=
ast
> the time required for dry materials to absorb liquid". (For all I know, y=
ou
> did say that and the rest was lost in translation.)
>
> Anyway, welcome to the list, guys, and please stick around. We have some
> glaze chemistry geeks here who we learn from and argue with and value
> immensely. Good science is always welcome here, as is the open exchange o=
f
> ideas -- that's the spirit of scientific inquiry.
>
> Yours
> Kelly in Ohio, a potter/writer married to a woodworking biologist, happy
> with one foot in art and one in science.
>
>
> http://www.primalpotter.com
>
>
> Click for home mortgage, fast & free, no lender fee, approval today//tagline.bidsystem.com/fc/CAaCDCZ64w8cLzk8GdrF62tJpKwmGftz/>
>
> http://www.primalpotter.com
>
>
> Click to lower your debt and consolidate your monthly expensesline.bidsystem.com/fc/CAaCDCZ6sVBOCfpBFDXMEYjUn3XFwY4q/>
>
> _______________________________________________________________
> Get the Free email that has everyone talking at http://www.mail2world.com
> Unlimited Email Storage =96 POP3 =96 Calendar =96 SMS =96 Translator =96 =
Much More!
>



--=20
Matthew Katz
Alfred, NY

Ron Roy on thu 29 mar 07


Lee,

I am under the impression that clay is usually seamed - in layers - did you
not say about some that there were layers of sand?

RR


> This is another reason while potter specific clay is better than
>industrial mixed clay. Because the clay comes out of the ground
>whole and it is only blundged and screened, it is never in an
>"unmixed" state.
>
>
>--
>Lee in Mashiko, Japan

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0

Ron Roy on fri 30 mar 07


Hi Bill,

When you talk about aging - is it in slip clay or clay ready for throwing?

RR

>To whom it may concern:
>
>
>I gave a presentation at NCECA in Louisville on clay and bodies. (Yes,
>I am the infamous Dr. Carty, although I never refer to myself that way.
>I am "Bill" to my friends and all the artists I interact with.) I also
>made comments on aging clays. I believe on the ClayArt discussion site
>however, my comments have been taken out of context. (I can't tell from
>the discussion if Phil was present, but he seems rather angry -- and I
>checked, I am using the word myth or mythology correctly according to
>Merriam-Webster's Collegiate Dictionary. I can elaborate if necessary.)
>
>
>Also, however, I believe it is really important for all of you to
>realize that the talks were not about aging! The question about aging
>came up in the short question and answer period at the end of talk and
>was just briefly addressed. If this is really of interest, and it may
>be, I would be happy to address aging at some future date. David Pier
>talked about things of importance to artists with regards to clay
>bodies. Matt addressed the importance of particle size on workability
>of clay bodies -- and yes, he had a fair number of great electron
>microscope images of clays and feldspars. And I talked about how the
>bodies fire and also touched, briefly, on the importance of mixing from
>observations on slumping. We did not address aging in our talks so you
>will likely be disappointed when the NCECA publication comes out.
>
>While I am not an artist (nor technically a scientist -- my background
>is ceramic engineering), I have worked with artists for roughly 20 years
>answering, to the best of my ability, questions regarding ceramics.
>Over time, too, my answers have sometimes changed based on observations.
>In all cases, I weigh the question and decide how to best answer the
>question. I have never disputed that artists may be able to feel
>differences that we are unable to measure, but my observations, and
>particularly those regarding aging and clay, have typically been tested
>and evaluated by artists. To all who know me, know that I am hands-on
>and eagerly enter into discussion on the way that things behave --
>particularly clays.
>
>Artists and industrial types pay a lot of attention to aging. As a
>result of both interactions with industry and with artists, we have
>evaluated aging from an experimental perspective. For this discussion,
>I believe it is necessary to define aging as change in behavior until
>steady-state is achieved. In other words, the clay may change with time
>until it stops changing. We (my research group and the Whiteware
>Research Center) have always been interested in measuring behavior, but
>more importantly, in mechanisms. We are much more interested in WHY
>something happens, rather than WHAT happens. From the perspective of
>why, we can help to understand better how to control the behavior or to
>compensate for changes in behavior. That seems to be something that
>artists find valuable.
>
>
>The common misperception (myth?) is that clay "ages" due to bacteria
>growth. I believe this was likely true 75 years ago or longer, but not
>for modern clay. While articles on aging have all but disappeared from
>recent literature (at least for industrial clay discussions), they were
>somewhat common up to the 1940s. I recall several articles specifically
>that grew bacteria in clay during the 1920s. The problem, however, is
>that it was not possible to explain why in some cases the clay would
>become easier to work and sometimes harder. The change in clay
>workability did not seem to be connected to bacteria growth based on the
>discussions in these articles, and frankly, the workability discussions
>were a bit vague. But that is not surprising, however, because the goal
>of article was to address bacteria growth.
>
>The mythology associated with ancient Chinese potters is that they would
>bury their clay in the ground for their grandchildren to allow the clay
>to age and have the best workability. This may have been true at one
>point, perhaps several hundred years ago, but does not seem to be the
>case any longer. Clay is produced in China much the same way as it is
>produced here in the U.S.: raw materials are mined, ground, mixed with
>water, worked into a plastic mass, then used. The mass production
>system does not really have mechanisms that allow for clay to be stored
>for months, let alone years, before use. I believe that is also true of
>artists in the U.S. Clay is purchased for use. Few artists have the
>storage capacity to keep enough clay to last for years of work. Typical
>clay storage is less than one year (based on a limited sampling of
>artists I know that I asked, but it make sense).
>
>Clay does age, but this aging, based on our observations (and a large
>amount of research and experimentation) is due to raw material
>dissolution and an increase in dissolved salts or ions. In a well mixed
>clay, this process is complete within a day or two at the most. The
>clay does not continue to dissolve with time due to the achievement of a
>sort of equilibrium or steady-state in the water chemistry. Of course,
>if the clay is poorly mixed, this process may take considerably longer,
>but the process is still likely done in less than a week.
>
>Furthermore, and perhaps most importantly, if the clay is obtained from
>a commercial vendor, and from my experience a vast majority of the clay
>used by artists comes from commercial clay suppliers, it has a limited
>window for aging. Whether the clay is purchased as a raw material from
>a supplier (such as Zemex or Unimin, etc.) or as a mixed body (such as
>from Laguna, or Trinity, etc.) then the clay is not likely be a good
>candidate medium for bacteria growth. There are two reasons, but one is
>sufficient: The clay has been mixed with tap water. Tab water
>typically contains, if nothing else, chlorine -- and chlorine kills
>bacteria. It is as simple as that. I have also been told that
>commercial clays contain an anti-bacterial agent, but have not verified
>this.
>
>
>The second reason is a practical one. A box clay, bought from a
>supplier or from a distribution retailer is of indefinite age, but it is
>quite unlikely that the clay will have set, in the box, for less than
>one week when the artist receives it. The clay body cannot be
>reasonably batched, mixed, extruded, boxed, and shipped in less than one
>week. It is likely considerably longer than that for the simple reason
>that these companies produce more than one or two bodies. Twenty bodies
>is more likely the case. It costs money to change the recipe, with mill
>clean-out, changing recipes, etc. The clay suppliers make as much clay
>as the market will bear at one time -- typically at least a few tons of
>clay. This clay then sits in a warehouse waiting to be shipped, or in
>the distributor warehouse waiting to be bought. Therefore, I would be
>surprised if the clay changes at all once in the hands of the potter or
>artist.
>
>In industry, however, things are different. Clay is produced in-house
>and it can get into the process immediately. Assuming that my argument
>that it takes a day for things to equilibrate (age if you like), this
>clay may appear to be different and changing in the industrial process.
>In these situations, it is possible that the clay will be changing,
>aging if you like, producing a non-uniform behavior with time. This
>problem shows up as increased loss rates for the simple matter that
>machines are unable to compensate for changes in the clay. If the clay
>is allowed to set, in the plastic state, even for only a day, these
>variations or changes are unnoticeable.
>
>That said, if an artist digs clay from a river bed and used the river
>water to mix the clay, then yes, aging due to bacteria is quite
>possible. Also, if you mix your clay using beer instead of water, that
>may be similarly true. However, again, if mixed using tap water, aging
>due to bacteria growth is quite unlikely. Note also though that not all
>tap water is the same. If an artist moves to a new location, changes in
>the water chemistry can cause changes in the workability and behavior of
>the clay.
>
>The fact is that aging for artists should not be a great problem.
>Changes that are seen could be due to several things, drying, changes in
>humidity, temperature of the clay, etc. However, I don't believe that
>aging is really an issue.
>
>Feel free to email me with questions. I will respond as quickly as I
>can.
>
>Cheers.
>
>Bill Carty
>
>carty@alfred.edu
>
>
>
>
>
>______________________________________________________________________________
>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.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0