Lee on tue 10 jan 12
Pete said it was okay to share this private email. I just removed
personal notes. This, and the next post will help clarify what RR
brought to our attention about Pete's thoughts about his clay body
research.
Hi Lee,
I have to make this quick- I have a meeting to go to. It's fascinating
to me that something I wrote in 2001 is still being passed around.
Those who imply that earthenware doesn't work for functional pots
(because it's seen as weaker than stoneware, etc.) are missing the
point about why we make and use handmade pots in the first place: we
do so for aesthetic reasons, and not purely practical ones. If
durability were the only criteria for picking a material then I'd be
working in injection-molded plastic. EVERY time we make a pot out of
clay and make it by hand we are making a STRONG statement that
aesthetic experience is important enough to justify compromising pure
practicality. This topic seems to come up often enough that it makes
me think that I ought to write a column.
Bottom line: humans have made and used earthenware vessels for
millennia and have fired them (depending upon the clay, the technology
and the desired results) to anywhere from cone 08 to cone 5 or 6. Like
ALL ceramic materials, earthenware has strengths and weaknesses and
savvy makers will use materials appropriately. We could easily argue
that porcelain is a lousy material for pots because it transmits too
much heat though the walls. So, for instance, in the case of a teabowl
this quality increases the risk of burning our customers hands and
porcelain teapots allow the tea to cool too quickly. Throw the bum
out! Obviously we are willing to take these qualities into account
when we make pots out of porcelain. As a parallel, a lot of very nice
(and highly valued) clothes are made out of silk or wool, which aren't
the most durable of materials in some respects- you sure can't throw
them in the washer and dryer. If functionality were all that mattered
then I'd be sitting here wearing polyester instead of the cotton (and
wrinkled) kakis or the wool sweater I'm currently wearing. I'd argue
that my cotton and wool clothing are quite functional, despite the
shortcomings inherent to both materials.
As for strength, earthenware has plenty for pots if it's used
appropriately. Remember, sophisticated makers tend to make sensitive
decisions based on the qualities of the finished material. As I've
argued in many private emails on this topic, what does it matter if a
given stoneware body is 50% stronger in MOR if the earthenware pot is
100% thicker? Many who work in earthenware tend to make thicker pots
because the qualities of the materials invite this.
One more issue: industrial research indicates that porous bodies tend
to chip before breaking and vitreous bodies tend to break before
chipping (these studies usually compared vitreous and so-called
"semi-vitrous" ware). This makes perfects sense if you understand the
ability of pores to interrupt cracking. Earthenware, stoneware and
porcelain each tend to fail in different ways. I own a lot of old
earthenware pots and many are chipped. My old stoneware and porcelain
pots have usually gone to the landfill in two or more pieces.
I work at all temperatures and love all clays, precisely because each
body and temperature has different qualities. We need to learn to
celebrate these varied qualities and take advantage of them while
avoiding the shortcomings that each clay or glaze possesses. I hope
this begins to address the issue.
Peter Pinnell
Interim Chair
Hixson-Lied Professor
Department of Art and Art History
120 Richards Hall
University of Nebraska
Lincoln, NE 68588-0114
(402) 472-5522
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Lee on tue 10 jan 12
This post directly addresses RR's questions about Pete's protocol. Enjoy!
Hi Lee,
Feel free to share my comments. As for not adjusting the figures to
take shrinkage into account, I didn't in 2001 but did in the fall of
2010 when I last taught the class (I never had the time to publish
that data- it's still in a big folder on my computer at school). In
the real world there was little difference on a 5/16" bar (the =3DA0wet
diameter of the bars we made)- the increased shrinkage was difficult
to measure with a micrometer and altered the final computed strength
very little. In fact, the differences were well within the margin of
error we got with different bars of the same clay bodies. In other
words, it made no difference.
Even if it had resulted in markedly different readings, I'll still
argue that the method we used is more useful for the real world of
pottery. We used the same die to extrude all the bars, fired each to
their maturing temperature and then simply recorded the amount of
force (weight in sand) that it took to break that bar when suspended
across a given span. My interest is in knowing which clay makes the
strongest bar. If it takes 20 lbss of sand to break one bar and 18
lbs. to break another, then the first clay is stronger. In other
words, if I make two pots from two different clay bodies and throw
them with exactly the same wall thickness, then which will be the
stronger pot? It's a simple real-world test in which the results are
directly applicable to pottery-making by hand.
The alternative is to compute the Modulus of Rupture (MOR) which
provides a comparable strength number (Pounds per square inch, for
instance). We added the MOR formula to an Excel spread sheet so MOR
was automatically figured when the diameter, span and breaking force
were entered into the sheet. MOR is a very useful figure for comparing
similar clay bodies (porcelain to porcelain) or comparing the results
of our own bodies with known published data. If we want an accurate
MOR value for our clays then naturally we have to accurately measure
the diameter of the fired bars and use that actual figure in the
formula- which we did. This method adjusts for shrinkage and
(ironically) results in a higher "strength" for clay bodies that
shrink more- there's an obvious numerical advantage to figuring the
MOR with a smaller diameter bar. So- when, in the real world, is it an
advantage for your clay to shrink more?=3DA0I completely understand the
value of figuring an MOR, but for my purposes I'd actually prefer to
have clay bodies that are strong and shrink less. The method we used
for the test is easily duplicated by any potter using stuff that
everyone has in the studio, and no math skills are necessary other
than being able to read pounds off a scale. And the results are easy
to see- stronger clays take more weight to break.
BTW, I learned one two thing this time. If you want to do one thing to
increase the strength of any fired clay, simply run it through a
de-airing pugmill. Off the top of my head I've forgotten how much, but
every clay was much stronger when it had been pugged. We can all put
forward our own theories why, but the difference was marked with every
clay.
All interesting stuff! Now if I only had time to make pots.
Pete
Peter Pinnell
Interim Chair
Hixson-Lied Professor
Department of Art and Art History
120 Richards Hall
University of Nebraska
Lincoln, NE 68588-0114
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Margaret Flaherty on wed 11 jan 12
A good example of why it's always rewarding to read what Pinnell has to
say....
On Wed, Jan 11, 2012 at 12:41 AM, Lee wrote:
> This post directly addresses RR's questions about Pete's protocol. Enjo=
=3D
y!
>
> Hi Lee,
>
> Feel free to share my comments. As for not adjusting the figures to
> take shrinkage into account, I didn't in 2001 but did in the fall of
> 2010 when I last taught the class (I never had the time to publish
> that data- it's still in a big folder on my computer at school). In
> the real world there was little difference on a 5/16" bar (the wet
> diameter of the bars we made)- the increased shrinkage was difficult
> to measure with a micrometer and altered the final computed strength
> very little. In fact, the differences were well within the margin of
> error we got with different bars of the same clay bodies. In other
> words, it made no difference.
>
> Even if it had resulted in markedly different readings, I'll still
> argue that the method we used is more useful for the real world of
> pottery. We used the same die to extrude all the bars, fired each to
> their maturing temperature and then simply recorded the amount of
> force (weight in sand) that it took to break that bar when suspended
> across a given span. My interest is in knowing which clay makes the
> strongest bar. If it takes 20 lbss of sand to break one bar and 18
> lbs. to break another, then the first clay is stronger. In other
> words, if I make two pots from two different clay bodies and throw
> them with exactly the same wall thickness, then which will be the
> stronger pot? It's a simple real-world test in which the results are
> directly applicable to pottery-making by hand.
>
> The alternative is to compute the Modulus of Rupture (MOR) which
> provides a comparable strength number (Pounds per square inch, for
> instance). We added the MOR formula to an Excel spread sheet so MOR
> was automatically figured when the diameter, span and breaking force
> were entered into the sheet. MOR is a very useful figure for comparing
> similar clay bodies (porcelain to porcelain) or comparing the results
> of our own bodies with known published data. If we want an accurate
> MOR value for our clays then naturally we have to accurately measure
> the diameter of the fired bars and use that actual figure in the
> formula- which we did. This method adjusts for shrinkage and
> (ironically) results in a higher "strength" for clay bodies that
> shrink more- there's an obvious numerical advantage to figuring the
> MOR with a smaller diameter bar. So- when, in the real world, is it an
> advantage for your clay to shrink more? I completely understand the
> value of figuring an MOR, but for my purposes I'd actually prefer to
> have clay bodies that are strong and shrink less. The method we used
> for the test is easily duplicated by any potter using stuff that
> everyone has in the studio, and no math skills are necessary other
> than being able to read pounds off a scale. And the results are easy
> to see- stronger clays take more weight to break.
>
> BTW, I learned one two thing this time. If you want to do one thing to
> increase the strength of any fired clay, simply run it through a
> de-airing pugmill. Off the top of my head I've forgotten how much, but
> every clay was much stronger when it had been pugged. We can all put
> forward our own theories why, but the difference was marked with every
> clay.
>
> All interesting stuff! Now if I only had time to make pots.
>
> Pete
>
> Peter Pinnell
> Interim Chair
> Hixson-Lied Professor
> Department of Art and Art History
> 120 Richards Hall
> University of Nebraska
> Lincoln, NE 68588-0114
>
>
>
> --
> Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>
> "Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97t=
hat is, =3D
"The
> land of eternal youth is behind the house, a beautiful land fluent
> within itself." -- John O'Donohue
>
Lee on wed 11 jan 12
On Wed, Jan 11, 2012 at 7:49 AM, Margaret Flaherty
wrote:
> A good example of why it's always rewarding to read what Pinnell has to
> say....
Anybody who has workshopped with Pete comes away knowing that he is
not only brilliant, he is generous with his knowledge.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Lee on wed 11 jan 12
Tony wondered if pugging clay would help it perform better in the
microwave. It probably does, because the clay become denser. I
wanted to make sure folks saw the last part of my second forward from
Pete. Pugging increases the strength of your clay.
I will start pugging my earthenware too, either cleaning the
pug between clays or getting another just for terracotta.
---------- Forwarded message ----------
From: Lee
BTW, I learned one two thing this time. If you want to do one thing to
increase the strength of any fired clay, simply run it through a
de-airing pugmill. Off the top of my head I've forgotten how much, but
every clay was much stronger when it had been pugged. We can all put
forward our own theories why, but the difference was marked with every
clay.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
May Luk on wed 11 jan 12
Hi Lee, or Tony & Clayart;
What is "perform better"? This needs to be clarified so that we are
comparing similar experience.
Comparing clay bars is good for an academic exercise and to further
our understanding. In the end of the day, how do we apply this info to
use? We don't eat off clay bars.
We also need to understand human behavior and consider the end-users.
We make wares to have somebody in mind, hopefully paying customers.
Wares come in different size and shapes, and temperature of food
varies. From heating lunch at day job for several years, I have never
have "good" experience (ie, the bowls are very hot and difficult to
carry to the serving table) with any types of clay and wares ( cone 6
stoneware, Chinese high-fire porcelain, US cone 6 porcelain, British
high-fire porcelain & stoneware, ceramics from mass market, hotel
wares) I always have to put a plate underneath in order to carry it to
my desk. (Maybe I should get myself a serving tray!)
If I buy ceramics for the microwave, I would like it to have:
1- handles on both sides for carrying from the oven to the table.
2- Oversize single loop handle
3- Flare out thick lips, not straight up & down wall
4- Generous sizing
5- white liner glaze
My 'better experience" to only fill the bowl 1/3 to half full for microwavi=
=3D
ng
Best Regards
May.
On Wed, Jan 11, 2012 at 11:19 AM, Lee wrote:
> Tony wondered if pugging clay would help it perform better in the
> microwave. =3DA0 =3DA0It probably does, because the clay become denser. =
=3DA0 I
> wanted to make sure folks saw the last part of my second forward from
> Pete. =3DA0 =3DA0Pugging increases the strength of your clay.
> =3DA0 =3DA0 =3DA0 =3DA0 =3DA0I will start pugging my earthenware too, eit=
her cleani=3D
ng the
> pug between clays or getting another just for terracotta.
>
>
> ---------- Forwarded message ----------
> From: Lee
>
> BTW, I learned one two thing this time. If you want to do one thing to
> increase the strength of any fired clay, simply run it through a
> de-airing pugmill. Off the top of my head I've forgotten how much, but
> every clay was much stronger when it had been pugged. We can all put
> forward our own theories why, but the difference was marked with every
> clay.
>
>
> --
> =3DA0Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>
> =3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=
=3D97that is=3D
, "The
> land of eternal youth is behind the house, a beautiful land fluent
> within itself." -- John O'Donohue
--=3D20
http://www.artspan.org/artist/mayluk
http://www.ceramicsbrooklyn.com/
Lee on wed 11 jan 12
On Wed, Jan 11, 2012 at 12:47 PM, May Luk wrote:
> Comparing clay bars is good for an academic exercise and to further
> our understanding. In the end of the day, how do we apply this info to
> use? We don't eat off clay bars.
A large range of our ceramics are not eaten off. With
"Grandma's pennies" not having copper in them any more, I have been
using a copper liner in my vases.
> If I buy ceramics for the microwave, I would like it to have:
> 1- handles on both sides for carrying from the oven to the table.
> 2- Oversize single loop handle
> 3- Flare out thick lips, not straight up & down wall
> 4- Generous sizing
> 5- white liner glaze
I am supposing number 0 is "Not ugly." As Pete mentioned, we
can't forget aesthetics.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
May Luk on wed 11 jan 12
Hi Lee;
I thought we were talking about microwave and crazing. Then what is
"perform better"?
Roll it down the hill and see which arrives to the bottom first?
"-)
It sounds nice talking about aesthetics on paper. (Teachers, Ugh!)
Just don't burn my hands and have me drop the bowl on the floor and I
have to clean it up.
I don't have anything against Pete. I live in the real world and I'm
not in school anymore. that's all. Thanks for the lecture,
nevertheless.
Best Regards
May
On Wed, Jan 11, 2012 at 4:58 PM, Lee wrote:
>
>
> =3DA0 =3DA0A large range of our ceramics are not eaten off. =3DA0 =3DA0 =
=3DA0With
> "Grandma's pennies" not having copper in them any =3DA0more, I have been
> using a copper liner in my vases.
>
>> If I buy ceramics for the microwave, I would like it to have:
>> 1- handles on both sides for carrying from the oven to the table.
>> 2- Oversize single loop handle
>> 3- Flare out thick lips, not straight up & down wall
>> 4- Generous sizing
>> 5- white liner glaze
>
> =3DA0 I am supposing number 0 is "Not ugly." =3DA0 As Pete mentioned, we
> can't forget aesthetics.
>
> --
> =3DA0Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>
--=3D20
http://www.artspan.org/artist/mayluk
http://www.ceramicsbrooklyn.com/
Lee on thu 12 jan 12
This is one of the first clay pieces I made, in terracotta. It is life siz=
=3D
ed.
I made it in my first clay class with Curt Hoard at the UofMn in 1990.
It is titled "Homage To A Hawaiian Shirt." It is a copy of my favorite
Hawaiian Shirt that disintegrated. This was also the year Paul
Wellstone was elected. I had this show in the Minnesota State Fair as
a part of the Northern Clay Show. An Aide to Paul Wellstone asked if I
would consider allowing this to be put in Wellstone's new D.C. office.
I said "SURE!" The Aide said that Paul wanted to have Minnesota art in
his office. The funding for this project never came through, sorry to
say. Much to my disappointment, his piece "disappeared" while I was
living in Japan. I am happy I have a photo of it!
http://bit.ly/wcSZBU
or
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/396282_101504866873970=
=3D
57_550727056_9129789_275267688_n.jpg
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Gerholdclay on thu 12 jan 12
I wonder if the apparatus that Pete is talking about to test clay strength =
h=3D
as been published anywhere? Is this a standardized test or just one Pete ha=
s=3D
developed?
This also sounds like a test that could be adapted to test strengh of clay =
j=3D
oins possibly resolving the long standing question of the best way to make=
s=3D
tong joins.
Paul
Sent from my iPad
On Jan 11, 2012, at 12:41 AM, Lee wrote:
> This post directly addresses RR's questions about Pete's protocol. Enjo=
y=3D
!
>=3D20
> Hi Lee,
>=3D20
> Feel free to share my comments. As for not adjusting the figures to
> take shrinkage into account, I didn't in 2001 but did in the fall of
> 2010 when I last taught the class (I never had the time to publish
> that data- it's still in a big folder on my computer at school). In
> the real world there was little difference on a 5/16" bar (the wet
> diameter of the bars we made)- the increased shrinkage was difficult
> to measure with a micrometer and altered the final computed strength
> very little. In fact, the differences were well within the margin of
> error we got with different bars of the same clay bodies. In other
> words, it made no difference.
>=3D20
> Even if it had resulted in markedly different readings, I'll still
> argue that the method we used is more useful for the real world of
> pottery. We used the same die to extrude all the bars, fired each to
> their maturing temperature and then simply recorded the amount of
> force (weight in sand) that it took to break that bar when suspended
> across a given span. My interest is in knowing which clay makes the
> strongest bar. If it takes 20 lbss of sand to break one bar and 18
> lbs. to break another, then the first clay is stronger. In other
> words, if I make two pots from two different clay bodies and throw
> them with exactly the same wall thickness, then which will be the
> stronger pot? It's a simple real-world test in which the results are
> directly applicable to pottery-making by hand.
>=3D20
> The alternative is to compute the Modulus of Rupture (MOR) which
> provides a comparable strength number (Pounds per square inch, for
> instance). We added the MOR formula to an Excel spread sheet so MOR
> was automatically figured when the diameter, span and breaking force
> were entered into the sheet. MOR is a very useful figure for comparing
> similar clay bodies (porcelain to porcelain) or comparing the results
> of our own bodies with known published data. If we want an accurate
> MOR value for our clays then naturally we have to accurately measure
> the diameter of the fired bars and use that actual figure in the
> formula- which we did. This method adjusts for shrinkage and
> (ironically) results in a higher "strength" for clay bodies that
> shrink more- there's an obvious numerical advantage to figuring the
> MOR with a smaller diameter bar. So- when, in the real world, is it an
> advantage for your clay to shrink more? I completely understand the
> value of figuring an MOR, but for my purposes I'd actually prefer to
> have clay bodies that are strong and shrink less. The method we used
> for the test is easily duplicated by any potter using stuff that
> everyone has in the studio, and no math skills are necessary other
> than being able to read pounds off a scale. And the results are easy
> to see- stronger clays take more weight to break.
>=3D20
> BTW, I learned one two thing this time. If you want to do one thing to
> increase the strength of any fired clay, simply run it through a
> de-airing pugmill. Off the top of my head I've forgotten how much, but
> every clay was much stronger when it had been pugged. We can all put
> forward our own theories why, but the difference was marked with every
> clay.
>=3D20
> All interesting stuff! Now if I only had time to make pots.
>=3D20
> Pete
>=3D20
> Peter Pinnell
> Interim Chair
> Hixson-Lied Professor
> Department of Art and Art History
> 120 Richards Hall
> University of Nebraska
> Lincoln, NE 68588-0114
>=3D20
>=3D20
>=3D20
> --
> Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>=3D20
> "Ta tIr na n-=3DC3=3DB3g ar chul an tI=3DE2=3D80=3D94tIr dlainn trina ch=
=3DC3=3DA9ile"=3DE2=3D
=3D80=3D94that is, "The
> land of eternal youth is behind the house, a beautiful land fluent
> within itself." -- John O'Donohue
Soj on fri 13 jan 12
I find this odd, as I routinely microwave all my stoneware, whether I thr=
=3D
ew
it or not, and have never had a bowl get so hot I couldn't handle it.
The only ware I've ever had this happen with was some older (like 40 or 5=
=3D
0
yrs old or possibly older) commercial dishware. I can't remember the mak=
=3D
er.
But this stuff got hot enough to cook on just from the heat of the plate=
=3D
.=3D20
It had belonged to my stepmother. I don't know what was in the clay that=
=3D
had been used to make the stuff but this stuff got volcano hot. I ended =
=3D
up
throwing it all away as I could not, in good conscience, even donate it d=
=3D
ue
to the risk of burning some unsuspecting child down the road, given the w=
=3D
ay
we all heat things up in microwaves these days.
I wonder what could be in the clay body that could cause this, as I have
never experienced it with any other substance in the microwave. Does
anybody have any guesses? I would like to actively avoid any clay body t=
=3D
hat
would behave this way...
On Wed, 11 Jan 2012 13:47:18 -0500, May Luk wrote:=
=3D
> ... I have never
>have "good" experience (ie, the bowls are very hot and difficult to
>carry to the serving table) with any types of clay and wares ( cone 6
>stoneware, Chinese high-fire porcelain, US cone 6 porcelain, British
>high-fire porcelain & stoneware, ceramics from mass market, hotel
>wares) I always have to put a plate underneath in order to carry it to
>my desk.
John Hesselberth on fri 13 jan 12
On Jan 13, 2012, at 5:54 AM, Soj wrote:
>=3D20
> I wonder what could be in the clay body that could cause this, as I =3D
have
> never experienced it with any other substance in the microwave. Does
> anybody have any guesses? I would like to actively avoid any clay =3D
body that
> would behave this way...
Hi Soj,
Water. Absorbed water. Microwave ovens are designed to very efficiently =3D
heat water.
Apparently your stoneware is well enough vitrified that it doesn't do =3D
this; however you even have to be careful with some stoneware bodies. If =
=3D
that are not formulated to be down to 2-3% absorption at their glaze =3D
firing temperature they can have the problem too. Earthenware, of =3D
course, normally has absorption levels of 6-10% when fired to the normal =
=3D
06-04 range.
Some people believe high iron glazes also cause the problem. I have =3D
never been able to duplicate their results with glazes containing up to =3D
12% RIO if the body was 2% or lower absorption. But there may be some =3D
conditions under which this happens.
Regards.
John
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with tools =3D
he is all" .... Thomas Carlyle
marci Boskie's Mama =3D^..^=3D on fri 13 jan 12
At 11:00 PM 1/12/2012, you wrote:
>From: Lee
>Subject: Re: Adventures in earthenware - PP
>
>This is one of the first clay pieces I made, in terracotta. It is life si=
z=3D
>ed.
>I made it in my first clay class with Curt Hoard at the UofMn in 1990.
>It is titled "Homage To A Hawaiian Shirt." It is a copy of my favorite
>Hawaiian Shirt that disintegrated.
(snip)
----
COOL piece, Lee. What is the coloring on it, other than the terra
cotta? Slip and mason stains?
marci the chinapainter
Edouard Bastarache on fri 13 jan 12
John,
"Earthenware, of course, normally has absorption levels of 6-10% when fired
to the normal 06-04 range."
Some doing earthenware accept a higher absorption,like 14 % at the Gien
Factory in France and they fire to cone 1. Naturally the pieces are
completely covered by glazes.
Gis,
Edouard Bastarache
Spertesperantisto
Sorel-Tracy
Quebec
http://www.flickr.com/photos/30058682@N00/
http://edouardbastarache.blogspot.com/
http://smart2000.pagesperso-orange.fr/bloggs_edouard.htm
http://www.facebook.com/edouard.bastarache
----- Original Message -----
From: "John Hesselberth"
To:
Sent: Friday, January 13, 2012 9:27 AM
Subject: Re: Adventures in earthenware - PP
On Jan 13, 2012, at 5:54 AM, Soj wrote:
>
> I wonder what could be in the clay body that could cause this, as I have
> never experienced it with any other substance in the microwave. Does
> anybody have any guesses? I would like to actively avoid any clay body
> that
> would behave this way...
Hi Soj,
Water. Absorbed water. Microwave ovens are designed to very efficiently hea=
t
water.
Apparently your stoneware is well enough vitrified that it doesn't do this;
however you even have to be careful with some stoneware bodies. If that are
not formulated to be down to 2-3% absorption at their glaze firing
temperature they can have the problem too. Earthenware, of course, normally
has absorption levels of 6-10% when fired to the normal 06-04 range.
Some people believe high iron glazes also cause the problem. I have never
been able to duplicate their results with glazes containing up to 12% RIO i=
f
the body was 2% or lower absorption. But there may be some conditions under
which this happens.
Regards.
John
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with tools he i=
s
all" .... Thomas Carlyle
Taylor Hendrix on fri 13 jan 12
Many, commercially produced plates are not made with stoneware or are
not fired to the optimum vitrification of the clay if it is stoneware.
This we know from reading and from common experiences. Several of my
plates purchased in Europe as seconds heat up a bit in the microwave
and show crazing probably from dishwasher usage. Our Polish pottery
plates come to mind.
Taylor, in Rockport TX
wirerabbit1 on Skype (-0600 UTC)
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/
https://youtube.com/thewirerabbit
On Fri, Jan 13, 2012 at 8:27 AM, John Hesselberth
wrote:
> On Jan 13, 2012, at 5:54 AM, Soj wrote:
>
>>
>> I wonder what could be in the clay body that could cause this, as I have
>> never experienced it with any other substance in the microwave. =3DC2=3D=
A0Do=3D
es
>> anybody have any guesses? =3DC2=3DA0I would like to actively avoid any c=
lay =3D
body that
>> would behave this way...
>
>
> Hi Soj,
>
> Water. Absorbed water. Microwave ovens are designed to very efficiently h=
=3D
eat water.
>
...
ivor and olive lewis on fri 13 jan 12
May Luc asks us the following question..
"What is "perform better"? This needs to be clarified so that we are
comparing similar experience.
Comparing clay bars is good for an academic exercise and to further our
understanding. In the end of the day, how do we apply this info to use? We
don't eat off clay bars."
Perhaps this is one issue that divides Artists from The Rest. May is right
to think that we need a higher degree of objectivity in the way information
is presented. Without objective qualification and quantification statements
such as "perform better" are subjective and bring no observations or
measurements to the workshop or studio that can be used to give credence to
the material we are using. Trust and confidence come from precision of
representations of what we believe to be valid facts.
Regards,
Ivor Lewis,
REDHILL,
South Australia
Eric Koenig on sat 14 jan 12
I haven't been able to find any specifics about which particular clay bod=
=3D
ies=3D20
heat up like that; but after searching around a little, I've found a tech=
=3D
nical=3D20
term for it that might help somebody to track it down:=3D20
thermal runaway.=3D20=3D20
Apparently, it happens in some ceramics and glasses (note that anything t=
=3D
hat=3D20
fuses and cools before it has a chance to form crystals is a glass). Fro=
=3D
m the=3D20
little I skimmed from various articles, there is some kind of heat feedba=
=3D
ck loop=3D20
instead of the heat properly dissipating, which is something I've never h=
=3D
eard=3D20
of. It can actually cause some of these materials to melt under high exp=
=3D
osure=3D20
to microwaves.
Eric
Lee on sat 14 jan 12
On Fri, Jan 13, 2012 at 9:35 AM, marci Boskie's Mama =3D3D^..^=3D3D
wrote:
> =3DA0COOL piece, Lee. What is the coloring on it, other than the terra
> cotta? Slip and mason stains?
Marci,
I didn't think anybody would look at it. ;^)
I used commercial engobe, underglaze and overglaze, and
the class clear, firing multiple times. It wouldn't fit in the
"common" electric kilns in the big room. Linda Sikora (She is at
Alfred teaching now) took me under her wing and fired it in the grad
students' electric that had an extended ring.
The shirt went missing while I was in Japan, but I have two
other pieces I made with it in my first clay class.
Hey, tonight, got accepted to a gallery I applied to a
couple years ago. My plan is to have new work there after my month
in Japan and trip to Korean after the spring:
http://thegrandhand.com/
See Hawaiian Shirt at these links:
http://bit.ly/wcSZBU
or
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/396282_101504866873970=
=3D
57_550727056_9129789_275267688_n.jpg
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
| |
|
