WeinhardtA@aol.com on fri 15 mar 96
I have done my job. I have spread the word. I have been the good apostle.
Clayart is now a household word among all those who know clay and know me.
Unfortunately, many of these same people see me as a well through which they
may tap that reservoir of knowledge that is Clayart. Being the good apostle,
I have tentatively agreed to help. (I am also passing out info on how to
connect to clayart!)
A friend of a friend (we'll call hime Mike) is interested in producing
flameware. Mike obviously has some knowledge of where he's going with this as
he has asked me to request information on flameware bodies that can be fired
in the cone 9 - 10 range. I have passed on to him that he should read Daniel
Rhodes' Clay and Glazes for the Potter which recommends firing to cone 11.
He has also asked about petalite but is for some reason interested in
"granular" petalite and a source for purchasing same in the S.E. Pennsylvania
area. I would assume that he will need some pointers on glazing or probably
slips.
Anything regarding flameware and petalite or successful substitutions and
glazes or slips would be extremely helpful. Though I only know "Mike" by
reputation, that reputation is good, a teacher who shares readily with
students and friends and I would like to do the same. Thanks very much!
P.S. As long as I'm on the subject of Flameware, there is a potter in
Southern Florida by the name of Regina Gurland who makes great ceramic woks
and stove-proof teapots. I haven't been able to find her phone number or
address so if any of you Floridians happen to know Reg, please say hi to her
for me and give her my address. She's one wonderful person!
Albert Weinhardt
99 Bowls of Tea on the Wall
11 Greenwood Place
Wyncote PA 19095
WeinhardtA@aol.com
Talbott on wed 25 sep 96
Flameware--what is it??? --how is it made????
Marshall Talbott
Pottery By Celia
Route 114
P.O. Box 4116
Naples, Maine 04055-4116
(207)693-6100 voice and fax
clupus@ime.net
Tony Hansen on sun 29 sep 96
The book "Ceramic Science for the Potter" has a good chapter on Thermal
Shock Bodies and the materials needed to produce them.
--
Tony Hansen, IMC - Pulishers of INSIGHT, FORESIGHT, Magic of Fire
thansen@mlc.awinc.com web: http://digitalfire.com/imc.html
Hasebe on mon 25 nov 96
During this year, sveral Japanese customers (almost all of Japanese I
talked) asked me a flameware casseroles at shows. Is flameware clay
commercially available ? (I do not want mix clay myself in a basement,
yet.)
It is snowing here, and I want to own one for Nabe (a kind of stew cook on
a table) this winter.
Thanks.
Hodaka Hasebe
Pittsford, NY
Phone 716-264-9698
e-mail Hasebeh@vivanet.com
Craig Martell on tue 26 nov 96
Hi: As you probably know already, Flameware is meant to be used on direct
heat, as on an electric stove or a stove using a gas flame. The formulating
and firing of Flameware bodies is tricky, at best. In the book Ceramic
Science for the Potter, West and Lawrence state that the lithium flux of
choice for Flameware bodies is Petalite, which matures at higher temps than
other types of feldspars. Thus there is a high failure rate of Flameware
bodies that are fired to cone 10. In order to reduce or minimize the failure
of Flameware bodies in use, they must be fired to cone 11. Then you have to
use lithium materials, such as spodumene or petalite in the glazes to make
them fit the low expansion Flameware body. I apologize for my long winded
reply and I'll get to the point. No, I am not aware of anybody mixing and
selling flameware clays as they probably don't want the liability(something
you should consider as well), and there is probably so little demand for
flameware clay from potters, that it wouldn't be worth taking the time and
effort to formulate and mix.
Perhaps there are commercial Flameware clays available and someone else will
answer the post and lead you to them. Another approach is to formulate the
clay body yourself and find a clay supplier to mix it for you. Ultimately, I
think you will find that the production of Flameware is technically VERY
challenging.
Kind Regards, Craig Martell-Oregon
Talbott on tue 26 nov 96
Many potters are leery of selling flameware due to the possible liabilities
involved with such a product-- I know this has nothing to do with your
questions but I thought I would mention it anyhow. ...Marshall
>----------------------------Original message----------------------------
>During this year, sveral Japanese customers (almost all of Japanese I
>talked) asked me a flameware casseroles at shows. Is flameware clay
>commercially available ? (I do not want mix clay myself in a basement,
>yet.)
>It is snowing here, and I want to own one for Nabe (a kind of stew cook on
>a table) this winter.
>
>Thanks.
>Hodaka Hasebe
>Pittsford, NY
>Phone 716-264-9698
>e-mail Hasebeh@vivanet.com
Marshall Talbott
Pottery By Celia
Route 114
P.O. Box 4116
Naples, Maine 04055-4116
(207)693-6100 voice and fax
clupus@ime.net
Tom Buck on wed 27 nov 96
Ron Probst wrote a piece on flameware for the 1975 book, The Studio Potter
and there was a discussion on Clayart within the past year, and one
knowledgeable person noted that flameware has to be very carefully
formulated or the internal stresses may cause the pot to explode suddenly
with disastrous results being possible. Please go to the archives and seek
this discussion.
Cheers TomB Hamilton ON Canada URL http://digitalfire.com/magic/tombuck.htm
LINDA BLOSSOM on fri 29 nov 96
Dear Marshall and Craig,
I own one of these pots. I bought it while living in Japan. It is a
wonder. I also have a ceramic type candle (or that flame in a little pot
stuff that campers use (can't think of the name for it)) burner that you
set the cooker on at the table. But just to say that the lidded cookers
are real and they do work. Also, they were very common there and I think
every family owned one. I suspect the body is public knowledge. But don't
expect anyone there to give you a recipe.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
blossom@lightlink.com
http://www.artscape.com
607-539-7912
Hasebe on sat 30 nov 96
Thank you much for info. I found posts related this matter in November
1995. I am surprised that many people mentioned about liabilities. In
Japan, Donabe, flameware is very common, and a popular item during winter
season. I visited Tokyo last month, and saw lots of them at department
stores. Anyway, I understand the concern and do not want to put myself in
trouble. So, I will make it for myself. I found a kind of recipy in
Japanese book, Petalite 30% and clay 70% fire at 1260C. For glaze, 60%
petalite and 40% feldspar. (I do not know the type of clay mentioned here,
though.)
If you go to Tokyo, try to visit Hiro Gallery Shun, (Sun Palace Building
1F, Closed Tuesday, Noon-7:00PM), held a solo exhibition of talented
potters every two weeks, I believe. Take Hibiya line to Hiro, use exit-1,
walk toward Tengenji. This gallery is very GOOD.
Hodaka Hasebe
Pittsford, NY
Phone 716-264-9698
e-mail Hasebeh@vivanet.com
LINDA BLOSSOM on mon 2 dec 96
Dear Hasebe-san,
Thanks for the recipe. Maybe I'll make sample batches using ball clay and
epk to see which might work. I bought my donabe casserole while I was
living in Yokosuka. I probably bought it in Kurihama, where our house was
located. Since Americans do not cook at the table, except fondue, they are
not familiar with flameware as the Japanese are. I have never had a
problem with mine and I would not be afraid to make and sell them, as long
as the recipe is correct. The glaze seems a little odd. No clay or
silica.
If you don't mind my suggesting, it would be easier to read your message
if it were not in all capitals.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
blossom@lightlink.com
http://www.artscape.com
607-539-7912
Craig Martell on mon 2 dec 96
In a message dated 96-12-02 09:57:30 EST, Linda Blossom wrote:
<< I have never had a
problem with mine and I would not be afraid to make and sell them, as long
as the recipe is correct. The glaze seems a little odd. No clay or
silica. >>
Hi Linda: OK, I guess you guys are going to make flameware, and I certainly
would not want to discourage you, and I am in no way making any judgments as
to your abilities at the technical level. I would suggest reading about
Lithium Thermal Shock Bodies in Ceramic Science for the Potter by Lawrence
and West. There is a lot of real solid technical information on developing
and producing Flameware. As I'm sure that you already know, this is very
technically intense ceramics. If I were doing this I would certainly be
prepared for CONTINUAL testing of my raw materials etc. You have to keep the
body and glazes stable in ware that is exposed to direct heat on an electric
or gas stove. Petalite is probably the most refractory type of Spar mineral
that is available to studio potters. According to my info, petalite has 8
moles of silica to 1 radical ox. The data presented by Lawrence and West
says that in order for petalite flameware bodies to survive direct heat, they
must be fired to cone 11 to fully involve the petalite in fusion. They state
that there is a high failure rate of petalite bodies fired to cone10. These
bodies have a very low coefficient of expansion, so glazes must be adjusted
to fit. That accounts for the odd compositions of flameware glazes.
Lawrence and West dicuss this as well. Also, plenty of bibliography and
cross referencing if you want to go deeper into the subject. I wish you the
best!
Kind Regards, Craig Martell-Oregon
LINDA BLOSSOM on wed 4 dec 96
Dear Craig and Ron, while I'm at it,
I didn't say I was going to make flameware. I only said I wouldn't be
afraid to do so. I'd go to Japan and after a lot of Sake, get someone to
give up their secrets. They don't give away recipes over there. While
everyone here says why something can't be done, others halfway across the
planet have been doing it very successfully for a long time. I just think
that it is better to talk to those who are doing it before pronouncing the
practice impossible.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
blossom@lightlink.com
http://www.artscape.com
607-539-7912
Craig Martell on wed 4 dec 96
In a message dated 96-12-04 07:54:24 EST, Linda Blossom wrote:
<< I just think
that it is better to talk to those who are doing it before pronouncing the
practice impossible. >>
I didn't say making flameware was impossible, I have a friend who did it
successfully for many years. I sure wasn't trying to discourage anyone
either, or I would not have sent references as to technical info. If anyone
on the list chooses to make flameware, It is my hope that you are completely
successful.
Over and Out: Craig Martell-Oregon-bracing up for the big wind today!
bkellyball@aol.com on tue 10 dec 96
SEVERAL YEARS AGO, MAYBE TWENTY, I MET A POTTER FROM NEW HAMPSHIRE NAMED
DICK STUDLEY WHILE HE WAS IN BOSTON....I BOUGHT SEVERAL PIECES AT THE
TIME....AND ALL BUT ONE ARE STILL IN USE TODAY...I CAN MAKE PERFECT RICE
ETC IN THESE FLAMEWARE POTS....I HAVE COOKED DIRECTLY ON THE STOVE,
ELECTRIC AND GAS AND HAVE NEVER HAD ANY PROBLEMS...WHEN I CONTACTED A
POTTER FRIEND IN DALLAS, HE SAID THE LIABILITY WAS TOO GREAT...A FEW YEARS
AGO, IN A TOWN NORTH OF DALLAS (MCKINNEY) I RAN INTO SOME MORE OF THESE
POTS...AGAIN BY DICK STUDLEY
BRIDGETTE BALL
Laurie Berkson on sun 5 oct 97
I know of a restaurant in NY City in search of some special pans made of
flameware.......anyone interested please contact me. Could be a good $ for
the right person......
Many Mused on mon 6 oct 97
a local restaurant (Frederick MD) once commissioned mugs from a local
potter, but the health department wouldn't let them use the mugs for serving
because the work had not been through formal industrial testing/certification
etc.-
just a heads-up before things get too far along.
douglas gray on wed 14 jan 98
This topic came up a while back. I'm reposting the information I found in
Daniel Rhodes' book, CLAY AND GLAZES FOR THE POTTER.
Overproof and flameproof bodies should
1. be formulated with as little silica as possible
2. include some feldspar in the body to take up any free silica
3. fire out at high temperatures, preferably at cone 10, 11 or higher
4. not contain appreciable amounts of iron
Aside from these factors, he suggests that rounded compact spherical forms will
resist cracking more than flat or sharp angled forms. The clay wall should be
consistent in its thickness and the glaze should fit without excessive
compression. He also suggests that the glaze should be applied to both the
inside and outside of the form.
Lithium can be used as a body flux because of its low coefficient of expansion.
Petalite is a natural lithium feldspar and can be used for 30 - 50% of the clay
body. Substitutions of spodumene have been tried with inconclusive results.
Rhodes gives one recipe.
flameware clay body, cone 11 (at least) either oxidation of reduction
petalite 45
feldspar 5
ball clay 35
stoneware clay 10
The test he gives for testing flameware is similar to the tests offered thus
far. Make a small flat dish about seven inches in diameter with walls about one
inch tall. Fire it. Fill it with water and place it on an electric hot plate
until all of the water has boiled away. let it sit for an additional 5 minutes
and then plunge it into cold water. If the body survives several cycles of this
then it may be considered flameproof.
============================================================================ =)
Douglas E. Gray, Assistant Professor of Art
P.O. Box 100547
Department of Fine Arts and Mass Communication
Francis Marion Univeristy
Florence, South Carolina 29501-0547
dgray@fmarion.edu
803/661-1535
F.Chapman Baudelot on wed 24 jul 02
--=======743F6EE6=======
Content-Type: text/plain; x-avg-checked=avg-ok-379C645; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: quoted-printable
Here in Spain people have always bought and used 'flameware' pots which can=
=20
be placed on a direct flame for cooking. Quite recently a large claybody=20
producer, Collet S.A., (I am using two of their products) brought out a=20
flameware body which is low fire and orange-coloured. There is a choice of=
=20
3 special commercial glazes to accompany it. Since it is extremely=20
difficult, costly and time-consuming to sue anyone here (as I well know!),=
=20
I bought one 10k pack of this clay and 2k of one of the special glazes. I=
=20
had almost forgotten I had this, but now that this thread has started up,=20
I'll try it at my own risk and let you all know the results if still alive=
=20
to tell the tale :) I'll try and throw some teapots since so many people=20
are inclined to keep the tea warm by leaving the pot on a hotplate or open=
=20
flame.
Fran=E7oise
http://indalopottery.tripod.com/fenix.html
--=======743F6EE6=======--
Pfeiffer, Dan R (Dan) on wed 16 nov 05
We would like to play a bit with making some flameware. I can find a number
of recipes from Ron and others but I have not found a source that sells a
moist clay. Not having a mixer I am not ready to jump into that just yet.
Maybe the next time a mixer comes up for sale in this part to the country.
So any clues as to who sells a good flameware clay? Seattle Pottery Supply
at one time did but I looked on the web page and it looks like they dropped
it.
I read lots of info in the archives on the risk of being sued and may only
make a few things for us and a few friends but would like to test it and see
how it works.
Thanks.
Dan & Laurel in Elkmont Al
Pfeiffer Fire Arts
Potters Council Members
UU KRC on wed 16 nov 05
I wonder if you have the same problem I was having
with the Seattle Pottery Supply website. At any rate
here is a link to their flameware
http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=11825-25&Category_Code=SC8MC
sorry I can't make it a link. Hope this helps.
I hate to admit this but the first dozen times I was
at the SPS website I did not notice that there are
often many pages of merchandise.
Jared
--- "Pfeiffer, Dan R (Dan)"
wrote:
> We would like to play a bit with making some
> flameware. I can find a number
> of recipes from Ron and others but I have not found
> a source that sells a
> moist clay. Not having a mixer I am not ready to
> jump into that just yet.
> Maybe the next time a mixer comes up for sale in
> this part to the country.
> So any clues as to who sells a good flameware clay?
> Seattle Pottery Supply
> at one time did but I looked on the web page and it
> looks like they dropped
> it.
>
> I read lots of info in the archives on the risk of
> being sued and may only
> make a few things for us and a few friends but would
> like to test it and see
> how it works.
>
> Thanks.
>
>
> Dan & Laurel in Elkmont Al
> Pfeiffer Fire Arts
> Potters Council Members
>
>
______________________________________________________________________________
> 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.
>
__________________________________
Yahoo! FareChase: Search multiple travel sites in one click.
http://farechase.yahoo.com
Ron Roy on thu 17 nov 05
Hi Dan,
I have never recommended that studio potters make flameware by the way - I
have always said it is too risky because we do not have adequate controls.
The reason clay makers don't sell flameware bodies is the same - it is too
easy for things to go wrong.
If you must there is information in Ceramic Science for the Potter by
Laurence and West.
It has been reprinted by Gentle Breeze publishing - - Axner will have it
for sure.
Note the firing range is higher than we usually go - like C11 or 12.
Good luck - RR
>We would like to play a bit with making some flameware. I can find a number
>of recipes from Ron and others but I have not found a source that sells a
>moist clay. Not having a mixer I am not ready to jump into that just yet.
>Maybe the next time a mixer comes up for sale in this part to the country.
>So any clues as to who sells a good flameware clay? Seattle Pottery Supply
>at one time did but I looked on the web page and it looks like they dropped
>it.
>
>I read lots of info in the archives on the risk of being sued and may only
>make a few things for us and a few friends but would like to test it and see
>how it works.
>
>Thanks.
>
>
>Dan & Laurel in Elkmont Al
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Lee Love on thu 17 nov 05
Dan,
I don't know if this will help, but you buy this kind of clay
here in Japan at the clay store as donabe clay, for making donabe pots
that sit on the fire. You can see photos of these pots on Google here:
http://tinyurl.com/9wwzu
They have petalite in them and are fired at a lower
temp. The young woman potter from Tokoname that was next to us at
the Mashiko festival was doing good business selling funky donabe
pots. She included an instruction sheet for their proper use with
each sale.
Next time I go to Akechi (where our non-Mashiko, imported
materials come from) I will pick up a bag and make myself a couple (one
for the house and one for the woodstove in the studio.)
Check out this article from The Studio Potter:
http://www.studiopotter.org/articles/?art=art0017
--
Lee Love
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
"Human subtlety will never devise an invention more beautiful,
more simple or more direct than does Nature, because in her
inventions, nothing is lacking and nothing is superfluous."
--Leonardo da Vinci
Pfeiffer, Dan R (Dan) on fri 18 nov 05
Thanks for the many ideas and the link. After ordering 100# I found the
shipping would be $80. :( I am not that interested so I will give up on it.
In talking to SP they think they are the only ones making a Flameware clay.
Maybe the next time I am in Seattle I will bring some home. We did get to
stop by their shop last year for a brief visit and was much impressed!
Dan & Laurel in Elkmont Al
Pfeiffer Fire Arts
Potters Council Members
>>>SP825 - FLAMEWARE - 25lbs
Code: 11825-25
Price:$9.50
Shipping Weight: 27.00 pounds>>>>
Lee Love on fri 18 nov 05
On 2005/11/18 2:53:10, ronroy@ca.inter.net wrote:
> The reason clay makers don't sell flameware bodies is the same - it
is too
> easy for things to go wrong.
Someone supplied this link earlier:
http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=11825-25&Category_Code=SC8MC
SP825 - FLAMEWARE - 25lbs
Code: 11825-25
Price:$9.50
Shipping Weight: 27.00 pounds
They offer it here in Japan too.
--
Lee Love
in Mashiko, Japan http://mashiko.org
http://seisokuro.blogspot.com/ My Photo Logs
"Where the spirit does not work with the hand, there is no art."
--Leonardo da Vinci
]
Edouard Bastarache on fri 1 jan 10
Hello all,
French site where they make flameware !!!
=3D
http://www.emilehenry.com/ifr/actualit%C3%A9/actualites/le-premier-wok-en=
=3D
-ceramique-flame
Leur p=3DE2te est aussi =3DE0 base de spodum=3DE8ne et de silice =3D
vitreuse.=3D3D
Their clay is also made up of spodumene and vitreous silica
Cordialement, Denis
Smart.Conseil
Le site Fran=3DE7ais d=3DE9di=3DE9 aux passionn=3DE9s de c=3DE9ramique
El sitio Franc=3DE9s dedicado a los amantes de la cer=3DE1mica
The French site dedicated to ceramics lovers
E-mail : smart2000@wanadoo.fr
Website : http://perso.wanadoo.fr/smart2000/
Forum Smart2000 : http://smart2000.diamonbb.net
Lee Love on fri 1 jan 10
You can buy flameware in Japan at the grocery store and buy the clay at the
claystore.
http://www.google.com/products?hl=3D3Den&q=3D3Djapanese+donabe+pot&sourceid=
=3D3Dn=3D
avclient-ff&rlz=3D3D1B3GGGL_enUS229US231&um=3D3D1&ie=3D3DUTF-8&ei=3D3DpSE-S=
8jCC4y4N=3D
o_ZpYwJ&sa=3D3DX&oi=3D3Dproduct_result_group&ct=3D3Dtitle&resnum=3D3D3&ved=
=3D3D0CCQQr=3D
QQwAg
--
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97that=
is, "Th=3D
e
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
david jenkins on sat 26 mar 11
To Lili and all flameware flamers,
Seattle Pottery Supply sells a flameware clay sp825. They have been=
=3D
=3D20
selling this clay for at least 25 years. When I talked to them a few ye=
=3D
ars ago=3D20
they knew of no flameware accidents or horror stories with their clay.=3D20=
=3D
The horror stories that you talk about are pottery myths that have b=
=3D
een=3D20
around for a long time but have no basis is truth. To use these stories=
=3D
as a=3D20
scare technique does a disservice to the truth and is nothing more than g=
=3D
ossip.
The problems with flameware are explained well by Vince, but even he=
=3D
has=3D20
to drag up past problems with exploding flameware without citing any of t=
=3D
he=3D20
actual incidents. Please let us know if there are any actual facts with n=
=3D
ames,=3D20
date, and outcomes.
Robbie Lobell is working with and selling flameware, and is doing a =
=3D
two=3D20
week workshop on flameware at La Merdiana in May. I don't think she mak=
=3D
es=3D20
the claim of it being appropriate for stovetop but calls it oven to tabl=
=3D
e ware.=3D20=3D20
She has an article in the summer/autumn issue of Studio Potter, call "A=3D=
20=3D
Flameware Journey". I think that Tom and Betsy Wirt do a line of flamewa=
=3D
re=3D20
at Coyote Clay in Minnesota. George Checopoulos at marrowstonepots has =
=3D
an=3D20
article on flameware clay and glazes in Ceramics Technical coming out in =
=3D
May=3D20
that we can all look forward to.
There are clearly a number of people who are interested in and worki=
=3D
ng=3D20
with flameware. To point out the technical problems and dangers is prude=
=3D
nt,=3D20
but to use unfounded horror stories does no good to anyone.
David Jenkins
George Chechopoulos on mon 28 mar 11
To David Jenkins: Thank you for your comments on Flameware David. However=
,
be careful purchasing what clay manufacturers call a "Flameware Clay Body."
I checked with Seattle Pottery today and asked them about the CTE value of
their Flameware clay body and the person I was talking to asked others ther=
e
and finally came back on the line to tell me that they do not have any data
concerning the CTE value of that clay body.
The CTE for ovenware should be below 3ppm and for stove top cooking it
should be below 2ppm. I prefer to keep it below 2ppm for any type of
cooking because if you say that it is Flameware someone is bound to try it
on the burner.
To Ron Roy: Thank you for your comments concerning alkaline earths and
cristobalite. Your information is always informative and accurate and can
always be trusted by the ClayArt group.
George J. Chechopoulos (Tsitsas)
Marrowstone Pottery
292 Merry Road, Box 193
Nordland, WA 98358
www.marrowstonepottery.com
www.youtube.com/marrowstonepots
email: marrowstonepots@waypoint.com
Bonnie Staffel on tue 29 mar 11
My take on the flameware possible disasters, having been in my business =3D
for
20 years I often had customers think that they could put my work on top =3D
of
the stove. Maybe they had old wives tales to fall back on, or were just =3D
not
thinking. However, on a recent TV sales pitch for some ceramic ware =3D
being
advertised, it was said that it could be put on top of the stove =3D
because it
was STONEWARE!!! So now what is the current "stoneware" potter to do?
educating the public never stops. It is really too much to ask the =3D
customer
to remember all this stuff, so they just go ahead with whatever the =3D
latest
information they heard was done, or they lost any paper work received =3D
from
the seller. The studio production potter from the earliest days had to
educate the customer even about the basic uses of their pots. Some
customers could think that the electric stove burner on "low" would be a
safe place on which to place plates to warm them for the dinner as one =3D
of my
customer's did. Of course, the plate broke.
Perhaps the horror stories have come from the above practices with =3D
ordinary
stoneware pots and even microwave cooking by the customer misusing the
pots..
I purchased a beautiful mug from a gallery and after heating my coffee =3D
in
the microwave, the mug came out all crazed. I was very disappointed as I
have been using Cone 6 fired pots regularly in the microwave with no
crazing.=3D20
.
As posted: =3D20
> The horror stories that you talk about are pottery myths that have
been
around for a long time but have no basis is truth. To use these =3D
stories
as a scare technique does a disservice to the truth and is nothing more
than gossip.
The problems with flameware are explained well by Vince, but even =3D
he
has to drag up past problems with exploding flameware without citing any =
=3D
of
the actual incidents. Please let us know if there are any actual facts =3D
with
names, date, and outcomes.
Robbie Lobell is working with and selling flameware, and is doing a =
=3D
two
week workshop on flameware at La Merdiana in May. I don't think she =3D
makes
the claim of it being appropriate for stovetop but calls it oven to =3D
table
ware. She has an article in the summer/autumn issue of Studio Potter, =3D
call
"A Flameware Journey". I think that Tom and Betsy Wirt do a line of
flameware
at Coyote Clay in Minnesota. George Checopoulos at marrowstonepots has
an article on flameware clay and glazes in Ceramics Technical coming out =
=3D
in
May that we can all look forward to.
There are clearly a number of people who are interested in and =3D
working
with flameware. To point out the technical problems and dangers is =3D
prudent,
but to use unfounded horror >stories does no good to anyone. David =3D
Jenkins
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD=3DA0 Throwing with Coils and Slabs
DVD=3DA0 Introduction to Wheel Work
Charter Member Potters Council
ivor and olive lewis on fri 1 apr 11
Inquisitive thoughts prompted me this morning as I was making coffee. I
wondered about the nature of the flame coming from the gas hob. The questio=
n
was, what sort of temperature are we applying to a utensil when we set it
above the flame. So I applied the pyrometer/multimeter to the tip of one of
the flames. Within thirty seconds the meter read 780 Deg C. (1436 F).
Beside the problems associated with Cristobalite and Quartz Phase Changes,
this would be above the Glass Transition Temperature (softening point) of
many of the glazes used by studio potters and ceramic artists.
Best regards,
Ivor Lewis,
REDHILL,
South Australia
George Chechopoulos on sun 3 apr 11
Ivor,
That was an interesting experiment that you performed on your burner. The
video that I posted on Youtube and have on my website shows my Flameware po=
t
being heated dry on a 15,000 btu Viking Stove burner. I have to heat the
pot on that burner for 15 to 20 minutes before I get above 600F and when th=
e
pot temp hits 680F (360C) or slightly below the temperature rise stalls and
won't go any higher in the pot given the burner output.
My Flameware Clay Body softening point is at 1217C and I have a Flameware
glaze with a softening point at 1118C. They both perform well together at
the cone 10 firing temperature. The glaze is pretty stable at that firing
temperature but I could try extending out the softening point a bit further=
.
George J. Chechopoulos (Tsitsas)
Marrowstone Pottery
292 Merry Road, Box 193
Nordland, WA 98358
www.marrowstonepottery.com
www.youtube.com/marrowstonepots
email: marrowstonepots@waypoint.com
James Freeman on sun 3 apr 11
On Fri, Apr 1, 2011 at 1:10 AM, ivor and olive lewis
wrote:
> The question
> was, what sort of temperature are we applying to a utensil when we set it
> above the flame. So I applied the pyrometer/multimeter to the tip of one =
of
> the flames. Within thirty seconds the meter read 780 Deg C. (1436 F).
>
> this would be above the Glass Transition Temperature (softening point) of
> many of the glazes used by studio potters and ceramic artists.
>
Ivor, et alii...
Though natural gas burning in air can easily run 1600-2700 degrees F,
depending on the efficiency of the burner, you will pretty much never heat
the vessel to that temperature, even in those spots where the flame directl=
y
impinges. As you are trying to heat those spots, the heat is fairly rapidl=
y
distributed throughout the entire vessel. Think of it sort of like
osmosis. Also, as the flame is adding heat, the vessel is dissipating it t=
o
the air. This is why you will probably reach a stall temperature, where th=
e
rate of increase from the burner is roughly balanced by the rate of
dissipation to the air.
Proof of this concept can be found in the common experiment of boiling wate=
r
in a paper cup, where despite direct flame impingement, the paper cannot ge=
t
hot enough to combust because the water is sucking away the heat as rapidly
as it is being applied. In much the same way, the entire mass of the
ceramic vessel is sucking heat away from the points where the flame
impinges.
Further demonstrations of this same concept can be found in the experiments
I performed and reported on several years ago to disprove the idea of uneve=
n
heating in an oven causing cracking of wares, wherein I boiled water in a
ceramic cup in under a minute by applying the flame of a 5000 degree
oxy-acetylene welding torch to the outside of the cup in order to
demonstrate that no part of the cup ever attained a temperature materially
different than any other part, nor of the contents.
Yet another demonstration occurred in Michael Wendt's experiment of a year
or two ago with nested vessels and thermocouples in his electric kiln, whic=
h
disproved the idea that wares in the kiln could be heated to materially
different temperatures depending on distance from the elements, and thereby
also disproving the idea that slowing the kiln at the end of firing could
allow the center of the kiln to "catch up".
In short, one cannot look solely at temperature. The governing physics
concepts are "heat capacity", which is the ability of the heated material t=
o
store that heat rather than dissipate it, and "thermal conductivity", whic=
h
is how fast the heated material can conduct that heat away from the heat
source and spread it out across other areas. In short, it is not simply a
matter of the temperature applied to the vessel, but rather a matter of
being able to pump heat into the vessel faster than it can be conducted awa=
y
from the hot spots and subsequently lost to the surrounding air. The
"thermal conductivity" works to try to prevent any one spot from being
significantly hotter than another (the K value I discussed in the
impossibility-of-differential-heating-in-an-oven thread to explain why it
just can't happen), while the "heat capacity" operates to try to dissipate
that heat away from the directly heated vessel and out to the surrounding
air and objects (the C value, which prevented materially uneven heating
within Mr. Wendt's kiln during his experiment).
None of this is to say that it is not possible to blow chunks out of an
improperly formulated body via direct flame impingement, but rather only to
point out that it would be pretty darned difficult to ever heat the vessel
in the open air to a point where you would start to melt the clay and glaze=
.
All the best.
...James
James Freeman
"...outsider artists, caught in the bog of their own consciousness, too
preciously idiosyncratic to be taken seriously."
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources
ivor and olive lewis on wed 6 apr 11
Dear James Freeman,
Thank you for your response (3 Apr 2011 21:59:01 -0400).
Yes, my illustration is simplistic. Yes, Physics rules the experience.
Would you agree that thermal shock can occur if there is a significant
temperature difference between the outside of the vessel and its contents i=
f
the rate of conductivity through the ceramic fabric low. Would you also
agree that Thermal shock can occur if there is a high value for coefficient=
s
of thermal expansion. And would you agree that the volumetric change during
a phase change of species of Silicon dioxide could induce fracture.
Sincere regards,
Ivor Lewis,
REDHILL,
South Australia
James Freeman on thu 7 apr 11
Ivor...
Yep, I agree with all three of your hypotheticals. I am sure they are all
theoretically possible if one set out to contrive such conditions. I was
only addressing the idea of melting or softening our clay or glaze with an
open flame.
All the best.
...James
James Freeman
"...outsider artists, caught in the bog of their own consciousness, too
preciously idiosyncratic to be taken seriously."
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources
On Wed, Apr 6, 2011 at 3:38 AM, ivor and olive lewis
wrote:
> Dear James Freeman,
>
> Thank you for your response (3 Apr 2011 21:59:01 -0400).
>
> Yes, my illustration is simplistic. Yes, Physics rules the experience.
>
> Would you agree that thermal shock can occur if there is a significant
> temperature difference between the outside of the vessel and its contents
> if
> the rate of conductivity through the ceramic fabric low. Would you also
> agree that Thermal shock can occur if there is a high value for
> coefficients
> of thermal expansion. And would you agree that the volumetric change duri=
ng
> a phase change of species of Silicon dioxide could induce fracture.
>
> Sincere regards,
>
>
> Ivor Lewis,
> REDHILL,
> South Australia
>
ivor and olive lewis on fri 8 apr 11
Dear George Chechopoulos
An interesting clip on U-Tube.
I am wondering if starting of with the bowl filled with ice water might
induce a greater degree of thermal stress on the fabric even though common
sense, exemplified by your images of food being cooked, would deny this
notion .
Best regards,
Ivor Lewis,
REDHILL,
South Australia
ivor and olive lewis on fri 8 apr 11
Dear James Freeman,
Thank you for your comment.
It would be an interesting exercise to set up an investigation to test thes=
e
ideas.
Sincere regards,
Ivor Lewis,
REDHILL,
South Australia
George Chechopoulos on mon 11 apr 11
Dear Ivor Lewis,
I don't think that freezing water in the Flameware bowl and then heating it
on the burner would increase the thermal stresses over heating it up dry as
I have done. However, it would make an interesting demonstration to video
record. I did that experiment a number of times with my first generation
clay body and it had no affect on the performance of the glaze or clay body
which had a water absorption rate of 7.5% (.075). However, I have not done
that same test on what I call my second generation glaze and clay body whic=
h
has a much lower water absorption rate of .7%(.007).
George J. Chechopoulos
Marrowstone Pottery
292 Merry Road, Box 193
Nordland, WA 98358
Website: www.marrowstonepottery.com
Youtube: www.youtube.com/marrowstonepots
Email: marrowstonepots@waypoint.com
Phone: 360-379-5169
ivor and olive lewis on wed 13 apr 11
Dear George Chechopoulos,
You may well be right drawing that conclusion from your observation. But
keeping the inner surface of the utensil at a uniform minimum temperature
will create the greatest temperature difference between the outer and inner
surfaces and hence, the steepest temperature gradient within the ceramic
fabric. This would induce the greater stress from differences in thermal
expansion
Do you have any values for the Coefficient of Thermal Expansion of the clay
bodies you are designing ?. Were that information available you would be
able to calculate the difference.
Regards,Ivor Lewis,
REDHILL,
South Australia
George Chechopoulos on fri 15 apr 11
Dear Ivor Lewis,
Yes, I have very good data for the CTE values for my clay body and glaze. =
I
have a digital dilatometer with computer interface that was being excessed
by NASA about a year ago now. I had it refurbished and tested by Orton
before shipping it to me so the accuracy of the instrument is very good. I
don't have to calculate the CTE because the program gives me the calculated
CTE readouts in chart form. The average CTE of my clay body from 26C to
400C is 1.56 x 10^-6 and my present glaze is at 1.35 over the same
temperature range. It's all in the article that will be coming out in May
in Ceramics Technical. I don't believe that the stresses will be greater
when heating the pot with ice in it on full burner strength than what I hav=
e
already done with a dry pot being heated to over 350C and then being plunge=
d
into ice water but I will perform the experiment a number of times and vide=
o
record the results. It won't be a very exciting video watching the ice mel=
t
in the pot. Give me a little time since I'm in the middle of getting ready
for a small experimental kiln firing (new glazes) then more dilatometer
testing followed by thermal shock testing and then a large kiln firing of
Flameware with the new glazes hopefully.
George J. Chechopoulos
Marrowstone Pottery
292 Merry Road, Box 193
Nordland, WA 98358
Website: www.marrowstonepottery.com
Youtube: www.youtube.com/marrowstonepots
Email: marrowstonepots@waypoint.com
Phone: 360-379-5169
ivor and olive lewis on mon 18 apr 11
Dear George Chechopoulos,
Thank you for your information. Your dilatometer marks the one I was using
in the mid fifties as a genuine polished brass antique category. The
controller had been built by the Laboratory Physicist.
By the way, if Cristobalite were present in a sample, would I be correct in
suggesting the intrusion of the phase change would be marked by a
discontinuity in the print out ?
I will try to obtain the next issue of C.T.
Sincerely,
Ivor
Ron Roy on mon 18 apr 11
Hi Ivor,
Download Peter Sohngens article - you can easily see cristobalite on
the charts when it is present.
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
RR
Quoting ivor and olive lewis :
> Dear George Chechopoulos,
>
> Thank you for your information. Your dilatometer marks the one I was usin=
g
> in the mid fifties as a genuine polished brass antique category. The
> controller had been built by the Laboratory Physicist.
>
> By the way, if Cristobalite were present in a sample, would I be correct =
in
> suggesting the intrusion of the phase change would be marked by a
> discontinuity in the print out ?
>
> I will try to obtain the next issue of C.T.
>
> Sincerely,
>
> Ivor
>
Neon-Cat on tue 19 apr 11
Congratulations, Ron, you=3D92ve got tridymite!
Re: the Peter Sohngens article for which you did the dilatometry,
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
Gentle, flowing, low-temperature curves characteristic of tridymite.
Some examples follow (ones easy to reference for our list).
There=3D92s a great example of a cristobalite peak for a quartzite sample
fired for 4 hours at 1450 C in fig 5 (similar to diffusivity, fig 3),
with a fractional linear change in fig. 4 that really shows off
expansion (scroll almost half-way down):
http://www.scielo.br/scielo.php?pid=3D3DS0366-69132002000300011&script=3D3D=
sci_=3D
arttext
The alpha-beta phase transition of quartz was first discovered at the
end of the 1800=3D92s by Le Chatelier. Around temperatures of 573 C,
quartz (SiO2) undergoes a phase change from the higher temperature
beta-phase to the lower temperature alpha-phase. This phase transition
is accompanied by a change in symmetry, volume, and shape, where the
beta-phase has higher symmetry and volume than the alpha-phase. We
know this and are aware of this phenomenon while firing =3D96 most texts
and books touch on the subject of alpha-beta quartz inversion. You can
see on a dilatometric chart the small but very obvious and
unmistakable quartz alpha-beta transition here (scroll to bottom of
page):
http://www.linseis.net/html_en/thermal/dilatometer/l76.php
Check out the brief discussion and examples of tridymite and
cristobalite dilatometric peaks beginning on page 9 of 12 and 10 of 12
under the heading =3D93Thermal Expansion=3D94 in an article for the governm=
ent
by NS Brodsky (1998). The specimens in this report were analyzed
using other test equipment that supported the dilatometry work (click
=3D91view document=3D92):
www.osti.gov/bridge/servlets/purl/663370-zbujaU/webviewable/663370.pdf
And finally, here=3D92s an article from a researcher who verified his
dilatometric findings with X-ray diffraction =3D96 there are excellent
chart comparisons showing tridymite (and a little quartz) for four
clays fired for 6 hours at 1350 C. See pages 3 and 4, under the
heading =3D93Firing of Clays=3D94 and compare this to your charts in the
Studio Potter article:
http://calteches.library.caltech.edu/94/1/Duwez.pdf
For those who might still be wondering about dilatometers try this,
it=3D92s pretty understandable.
PRINCIPLES OF PUSH-ROD DILATOMETRY
Anter Corp. (Technical Note #69)
www.http://anter.com/TN69.htm
Look at what they offer in the way of testing services (bottom of the
page link).
Orton offers dilatometers.
http://www.ortonceramic.com/instruments/05aDilatometer.shtml
Their site says they can perform a variety of analyses:
=3D95 Calculate the coefficient of thermal expansion (CTE) between
specified temperatures, or a series of specified temperatures
=3D95 Calculate the average coefficient of thermal expansion from room
temperature to a specified temperature at a specified temperature
increment
=3D95 Determine glass transition temperature (for ceramic glasses with
TG's between 400=3DB0C and 850=3DB0C)
=3D95 Determine softening temperature
=3D95 Locate alpha-beta quartz transition
=3D95 Export the data in a text file format for independent analysis or
archiving purposes
You will note they limit their bragging rights to locating the
alpha-beta quartz transition.
Folks do train at universities to use this thermal technique of
dilatometry properly and even then there are many drawbacks to the
instrument and many tricks of the trade. One can get a pretty good
on-line education at least as far as silica polymorphs goes by reading
course work from various engineering schools. Tridymite has been known
for years, studied extensively, and there is certainly no lack of data
on it available to any potter or clay worker. For someone claiming
that we=3D92re overrun with cristobalite it would only seem prudent to
inform oneself about the possibilities of tridymite and be able to
differentiate its signature from that of cristobalite in samples
verified to contain actual cristobalite and tridymite. Tridymite is
what we will find most often in our fired clay bodies at the
temperatures at which we work should any leftover silica get the idea
to morph-off. And tridymite really is no big deal for us.
Marian Gooding
Neon-Cat Ceramics
www.neon-cat.com
Ron Roy on tue 19 apr 11
Call it what ever you want - the fact remains - that expansion happens =3D2=
0
at ovenware temperatures. The article explains how to avoid that =3D20
problem.
I have all the samples here - anyone want to have them analyzed?
RR
Quoting Neon-Cat :
> Congratulations, Ron, you=3DE2=3D80=3D99ve got tridymite!
Neon-Cat on tue 19 apr 11
Ron, calling it what it is (tridymite) might reassure rather than
terrorize potters and other clay workers. There are important
differences between tridymite and cristobalite. Probably the most
important has to do with volume change during displacive phase
transformations (alpha <-> beta also called low <--> high).
The temperature-initiated displacive transformation of quartz at 573 C
(1063 F) has a volume change associated with it that averages 1.6%.
The displacive transformation of high-middle tridymite at 160 C (320
F) has a volume change of 0.3%; the middle-low tridymite displacive
transformation at 105 C (221 F) has a volume change of 0.8% (total
high-low 1.1%).
Compare this to the volume change at 200-270 C (392 =3D96 518 F)
associated with the high-low cristobalite displacive transformation of
>3%. That=3D92s a big difference. Should any leftover quartz engage in
reconstructive transformation thank goodness we=3D92ll have the small
volume change associated with tridymite during its displacive
transformations. Quartz and cristobalite are dangerous (possible
fracture or weakening of pots), tridymite is not. As an example, take
silica bricks that are used for high-temperature applications =3D96 when
they=3D92re made a small amount of the alkaline earth compounds CaCO3
(calcium carbonate, aka whiting) or calcium oxide (CaO) are added as
flux to dissolve the quartz and precipitate the SiO2 as tridymite. In
service the tridymite has much less shrinkage during displacive
transformation than either quartz or cristobalite so the refractory
bricks avoid fracture or weakening.
Just to touch on a few more differences between cristobalite,
tridymite, and quartz, I=3D92ll give just a couple of more brief examples.
The structure of quartz, tridymite, and cristobalite are different.
Bonding within the clay body may be affected; the placement of cations
may be influenced, internal stresses within the clay body may be
influenced, etc., etc. Cristobalite is a symmetric cubic structure
and is isotropic. Tridymite and quartz have different structures and
are anisotropic (their expansion differs along different
crystallographic directions). There is a correlation between the
melting temperature of a clay body and the linear thermal expansion
coefficient of the materials that make it up, especially those with
more closed structures. Both melting temperature and thermal expansion
are influenced by bond strength and the magnitude of thermal
vibrations set of during firing. As bond strength increases, the
melting temperature increases, and the thermal expansion coefficient
decreases.
The density is different for each silica polymorph. For example, high
quartz has a density of 2.65 g/cm3. High tridymite has a density of
2.26 g/cm3. High cristobalite has a density of 2.32 g/cm3. The
higher-temperature polymorphs have the lower densities, reflecting
their more open structures. In a mixed-material, ceramic body where
there might be more than one crystalline phase and a noncrystalline
phase each material=3D92s density is based on the atoms present and the
packing arrangement of the atoms. Among other things the density of
individual constituents affects the overall bulk density of the fired
pot which then impacts the porosity and water absorption of the pot.
Anyway, I am sick of science now. Those interested can study on their
own. I think you get the idea =3D96 it does make a difference what we have
formed in our ceramics and we should have a general idea of what is
and is not possible. Tridymite is =3D93in=3D94. Cristobalite is =3D93out=3D=
94. Life=3D
as
a potter or clay worker is much, much better without undue fear of
cristobalite.
I've been meaning to thank George C. for putting up a little
information about his flameware work. While not for me, it's
interesting -- I like to read about what others are doing.
Congratulations on your upcoming article!
Marian Gooding
Neon-Cat Ceramics
www.neon-cat.com
On Tue, Apr 19, 2011 at 1:54 PM, wrote:
> Call it what ever you want - the fact remains - that expansion happens at
> ovenware temperatures. The article explains how to avoid that problem.
>
> I have all the samples here - anyone want to have them analyzed?
>
> RR
Ron Roy on wed 20 apr 11
Again - call it what you want - potters usually just call it
cristobalite just to keep things simple - nothing wrong with that -
Here is what the Hamers says in the chapter on silica - 10 pages of
essential information for potters on the most important oxide we use.
"The potter may meet with another phase of silica called tridymite.
Tridymite is a complex phase having two major subdivisions and nine
minor subdivisions called forms. Quartz converts to tridymite between
870c and 1470c (1598f and 2678f)if suitable catalysts are present. It
cannot exist indefinitely above 1470c but at this temperature begins
to convert to pure cristobalite. On cooling tridymite will remain as
tridymite at atmospheric pressure. If under greater pressure,
tridymite will convert back into quartz which is a denser phase. For
this reason very little tridymite occurs as a natural mineral.
Tridymite has industrial application as silica bricks and in
combination with cristobalite in earthenware bodies. The inversion
properties of it's nine forms combined with cristobalite can give
control of a tendency to craze coupled with a resistance to thermal
shock.
Tridymite and disordered cristobalite can obviously exist side by side
at temperature below 1470c. The same catalysts that assist the
conversion of quartz to tridymite also act as a catalyst of both into
disordered cristobalite. Therefore the easiest way is to consider
these conversions from quartz to tridymite, disordered cristobalite
and pure cristobalite as one and include these phase changes under the
name cristobalite."
So when I say cristobalite you now know what I mean - not that it
means any difference to the outcome - or how to deal with it.
RR
Quoting Neon-Cat :
> Ron, calling it what it is (tridymite) might reassure rather than
> terrorize potters and other clay workers. There are important
> differences between tridymite and cristobalite. Probably the most
> important has to do with volume change during displacive phase
> transformations (alpha <-> beta also called low <--> high).
ivor and olive lewis on thu 21 apr 11
Dear Ron, in part of your quotation Hamer uses the term "Disordered" to
describe Cristobalite. So I flipped the pages and only found
"Disordered"used in connection with Kaolin. In this context atoms of other
elements are substituted in the Kaolin crystal lattice, Is Hamer telling us
the same thing happens with Silicon dioxide ? If not, what is "Disordered
Cristobalite"?
I note that in his section on Cristobalite he tells us that "Cristobalite
does not expand at a constant rate when heated from room temperature. In th=
e
first 200 deg C it expands approximately 0.7% volumetrically. Then at 226
deg C it suddenly expands by 3%" There are two diagrams illustrating this
for heating and cooling.
James Freeman on thu 21 apr 11
Ivor, Ron...
This may help: http://www.minsocam.org/ammin/AM49/AM49_952.pdf
Seems the cristobalite/tridymite relationship is rather complex, and cannot
really be looked at without also looking at the other minerals in our clay
bodies. The key seems to be with the various (and varying) fluxes. Quite
interesting.
(Preemptive note to certain combatants: Please, please don't argue with ME=
,
as I have nothing to do with this argument, and I really don't care. Argue
with the paper I shared if you wish. Dismiss it because of it's date of
publication if you wish. Call the authors stupid or uninformed or behind
the times if you wish. Just please leave me out of it.)
All the best.
...James
James Freeman
"...outsider artists, caught in the bog of their own consciousness, too
preciously idiosyncratic to be taken seriously."
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources
On Thu, Apr 21, 2011 at 3:20 AM, ivor and olive lewis u
> wrote:
> Dear Ron, in part of your quotation Hamer uses the term "Disordered" to
> describe Cristobalite. So I flipped the pages and only found
> "Disordered"used in connection with Kaolin. In this context atoms of othe=
r
> elements are substituted in the Kaolin crystal lattice, Is Hamer telling =
us
> the same thing happens with Silicon dioxide ? If not, what is "Disordered
> Cristobalite"?
>
> I note that in his section on Cristobalite he tells us that "Cristobalite
> does not expand at a constant rate when heated from room temperature. In
> the
> first 200 deg C it expands approximately 0.7% volumetrically. Then at 226
> deg C it suddenly expands by 3%" There are two diagrams illustrating thi=
s
> for heating and cooling.
>
Neon-Cat on fri 22 apr 11
That was sweet, you're welcome, Ivor!
Marian
On Fri, Apr 22, 2011 at 8:57 PM, ivor and olive lewis
wrote:
> Dear Marion,
> Thank you for clarifying the term "Disordered" in the context of Silicon
> Dioxide structures.
> Best regards.
> Ivor Lewis,
> REDHILL,
> South Australia
Ron Roy on fri 22 apr 11
Hi Ivor,
I have no idea what disordered cristobalite is - I have to assume it
is different from pure but how and why I don't know.
We also have to understand that we are dealing with thicknesses of
clay - the silica at the surface of the clay goes through it's
inversion at a different time than the silica in the interior - I
think that explains the evenness of that curve.
Keep in mind - I have done hundreds of runs on both clays and glazes -
fired by me and by others - I have yet to see anything that makes me
think there are any problems with the results I am getting.
Couple that with the calibrations I do every 50 runs or so using a
fused alumina rod supplied by Orton and I am confident the results I
am getting are reliable.
Care to do some experiments to clarify some of your questions? Sample
preparation is simple.
RR
Quoting ivor and olive lewis :
> Dear Ron, in part of your quotation Hamer uses the term "Disordered" to
> describe Cristobalite. So I flipped the pages and only found
> "Disordered"used in connection with Kaolin. In this context atoms of othe=
r
> elements are substituted in the Kaolin crystal lattice, Is Hamer telling =
us
> the same thing happens with Silicon dioxide ? If not, what is "Disordered
> Cristobalite"?
>
> I note that in his section on Cristobalite he tells us that "Cristobalite
> does not expand at a constant rate when heated from room temperature. In =
the
> first 200 deg C it expands approximately 0.7% volumetrically. Then at 226
> deg C it suddenly expands by 3%" There are two diagrams illustrating thi=
s
> for heating and cooling.
>
Neon-Cat on fri 22 apr 11
Dear Ivor and list, you can find images, diagrams, and descriptions of
disordered cristobalite in recent publications and texts . In the case
of cristobalite, the disorder spoken of is one of orientational
disorder =3D96 bond angles are a tad off or short-range stacking is
slightly off or bonds lengths are shortened a bit from the expected.
Some researchers liken the structure of Beta-cristobalite over certain
ranges to that of silica glass as opposed to that of
Alpha-cristobalite. Researchers continue to debate the finer points of
cristobalite, tridymite, and other less common silica polymorphs. The
fact still remains that tridymite and cristobalite are two separate
and distinct polymorphs each with their own properties -- as
different as apples and oranges. To lump cristobalite and tridymite
together and call them both cristobalite is insanity and does our
field no good service. I gave several good reasons why we should not
be lulled into thinking that any rise in a dilatogram in the region of
cristobalite and tridymite should just be considered cristobalite. Why
work to remove something (tridymite) that is not a problem?
Many decades ago Seger gave us some rules that are still followed by
many as regards the use of thermal data and they involve the
coefficient of thermal expansion (CTE). The CTE, as determined by
dilatometry, is the slope of a line at any temperature. The
measurement of CTE, by the way, is influenced by the thermal history
of the fired clay body and other things. In real life we look at well
prepared samples and processes and documented charts with completed
CTEs for clay bodies when considering their worth as far as specific
service goes and when adjusting glaze-clay body fit. You glaze buffs
use programs to supply CTE information to you and debate sources and
availability for the CTEs of less common materials. Why Ron/Sohngen
did not give us in the Studio Potter article the CTE as determined for
each clay sample is beyond me. Ron/Sohngen give us only =3D93percent
linear thermal expansion=3D94 and talk of flattened curves, steeper
curves, humps, and bumps as they attempt to tell us that some of the
samples contain cristobalite when they clearly do not. What they
discovered was tridymite, a non-threat to pots because if it inverts
at all through displacive phase transformation the volume change
associated with this transformation is low (high forms may remain as
metastable forms even at room temperature =3D96 they don=3D92t have to
invert). Ron=3D92s mumble-jumble that =3D93cristobalite=3D94 means cristoba=
lite
and tridymite is so absurd. If I sent a sample to a reputable lab to
be analyzed for the products created in a fired sample and it
contained tridymite, the lab would not send me results saying, =3D93you=3D9=
2ve
got cristobalite!=3D94 Grade school students and those in higher
institutions these days are taught the three main phases of silica
(quartz, tridymite, and cristobalite) in introductory geology,
chemistry, environmental science, health sciences, and related fields.
To now want to debate the existence of tridymite or attempt on this
list to debate the finer points of each silica polymorph or to rehash
decades of progressively established fact is a dodge of the original
claim made in the Studio Potter article (our clay bodies have that
dreadful cristobalite unless you do things our way). We might as well
have elephants in the clayart room next year, along with the donkeys
and flamboyant boas, if anything goes in our thinking. Make those
elephants pink, please.
When trying to fit a glaze to a clay body we typically (should) look
at the CTE of the clay body and that of the glaze. A good fit has the
CTE of the glaze 5-15% (10% is said to be ideal) lower than that of
the clay body. This has been a standard popular method for many
decades. The data necessary to consider proper clay body-glaze fit is
not provided in the Ron/Sohngen article as they attempt to show you
cristobalite that doesn=3D92t exist and tie its production to glaze-clay
body failures and failures of pots in the oven.
The greatest factor affecting thermal shock resistance is the
coefficient of thermal expansion (CTE). The lower it is, the better.
There is a handy formula for calculating thermal shock resistance that
utilizes the coefficient of thermal expansion (CTE). Ceramic engineers
have compiled table after table of data on the physical and mechanical
properties of specific materials, from glasses, to oxides, to known
named substances, minerals, etc. For example, quartz and cordierite (a
magnesium silicate, 2MgO-2Al2O3-5SiO2) both have very low CTEs. In the
case of cordierite it has a negative CTE along the c-axis (it=3D92s
anisotropic) and an open structure. When it is heated thermal energy
is absorbed by rearrangements of its tetrahedral units through their
tilting and/or rotation. So if we are making cordierite in a clay body
(cone 13 plus) the overall CTE of the clay body will be reduced. Many
thermal shock resistance ceramics make use of cordierite. By the way,
the dilatometric chart of cordierite is a straight, steep line. One
just does not compare the =3D93look=3D94 of charts, or their visual
similarities as Ron & Sohngen did when trying to compare clay bodies =3D96
we use their calculated CTEs to compare thermal expansion.
In any case, try this article on disordered cristobalite. I=3D92ll leave
you to find others on you own.
http://web.me.com/dove_family/martin/publications/PRL_1993_Ian.pdf
Cordierite: http://www.ferroceramic.com/Cordierite_table.htm
Marian Gooding
Neon-Cat Ceramics
www.neon-cat.com
ivor and olive lewis on sat 23 apr 11
Dear Marion,
Thank you for clarifying the term "Disordered" in the context of Silicon
Dioxide structures.
Best regards.
Ivor Lewis,
REDHILL,
South Australia
George Chechopoulos on sat 23 apr 11
Dear Marian,
I'm fairly new to this group so I'm not familiar with a lot of the past
interaction between the members but I really wish you would eliminate your
interspersion of negative and disrespectful comments that have been
interlaced through some of your technical dissertations. There are better
ways of disagreeing with the opinions of other members of the group without
being insulting no matter how ridiculous you think they may be. I sometime=
s
have that same tendency, especially after reading the current issue of the
Ceramics Monthly Techno Files which I intend to comment on to the Editor
(dumb glazes) but I have my wife who insists on reviewing and censoring out
all of my inflammatory remarks. I'm afraid that your kitty cats just aren'=
t
very good at that.
In reference to your comments on Friday, April 22nd I have the following
comments and questions:
If we are talking about Flameware Pottery (Stove Top and Oven use) then any
hump at low temperature (~177C to 204C) makes a big difference and I really
don't care what you call it. Since Dilatometry can't tell you exactly what
polymorph of silica it is I prefer to call it "Cristobalite" and to create =
a
true Flameware clay body I want to get rid of it entirely to prevent even
the remotest possibility of breakage through that temperature range. Sorry
Marian, I'm sure you are shuddering at this point. My degree is in
Architectural Engineering not Chemistry.
Other than that I thought that what you had to say was very useful in
relation to Flameware Pottery but I don't think that Peter Sohngen's articl=
e
had anything to do with Flameware or glazes, thus why would he have needed
to bother with CTE values? Did I miss something again? In particular, I
found your comment on the CTE for glaze fit of 5-15% (10% being ideal) lowe=
r
than that of the clay body of particular interest to me. Based on my
experiments thus far, 10% appears to be about right but do you have any goo=
d
references for those percentages? If so, it would be helpful to me.
George J. Chechopoulos (Tsitsas)
Marrowstone Pottery
292 Merry Road, Box 193
Nordland, WA 98358
www.marrowstonepottery.com
www.youtube.com/marrowstonepots
email: marrowstonepots@waypoint.com
Neon-Cat on sat 23 apr 11
George, with regard to 'the CTE for glaze fit of 5-15% (10% being
ideal) lower than that of the clay body', probably the easiest
reference for potters is the W. G. Lawrence & R. R. West book "Ceramic
Science for the Potter", second edition, if you can find it. I'd put
up the relevant passages but have some things I need to do in the next
few days. Seger's rules became the basis for much of industry thinking
for many years and then spilled into some studio potter books to
influence thought in our realm.
I think it is absolutely wonderful that Ron Roy has shown us that our
clay bodies are free of cristobalite. Tridymite is ever so much more
user friendly. Hallelujah!
Marian
Neon-Cat
George Chechopoulos on sun 24 apr 11
Marian,
Thank you for that reference from "Ceramic Science for the Potter." That
book was my starting point for Flameware research about two years ago but m=
y
reading of the book was very selective and not complete at the time. That
information probably would not have made much of an impression on me at the
time because it was before my purchase of the dilatometer and my
experiments. At this point it makes more sense to me and I can now go back
to my output data and calculate the expansion difference between my clay
body and glaze even though I know that my product works fine based on the
thermal shock testing that I have performed thus far.
George J. Chechopoulos
Marrowstone Pottery
292 Merry Road, Box 193
Nordland, WA 98358
Website: www.marrowstonepottery.com
Youtube: www.youtube.com/marrowstonepots
Email: marrowstonepots@waypoint.com
Neon-Cat on mon 25 apr 11
George, while I am of course delighted that you have found the
information of use, I posted an answer to your question for fellow
list members - in general - because of the historical significance of
Seger=3D92s work and its influence, past and present. While quite nice in
some sections, "Ceramic Science for the Potter" is dated and thus not
an end-all text as the field of ceramic science continues to progress,
deepen, and expand.
As to your earlier post, I am not mollified by your =3D91thank you=3D92 now=
.
However, I am very glad to have read that first post =3D96 it=3D92s always
nice to get a hint of the measure of a man.
Marian
Neon-Cat Ceramics
=3D93We dance round in a ring and suppose.
But the secret sits in the middle and knows.=3D94
(Robert Frost, The Secret Sits, "A Witness Tree", Poem #681, 1942)
Bill Merrill on tue 26 apr 11
Ron Probst did a lot of flameware tests. The Spodumene used today is
quite different than the Spodumene I used over 35 years ago. When a
fusion button was done, the thimble shaped fusion button grew over
double in height and diameter. The color was a beautiful orange color.
Todays spodumene is something that needs to be tried, but it is not the
same. The problem with hand thrown Flameware is if the body is not an
even thickness, it is likely it may not work so well. What happens is
and has to Wally Schwab is there can be an explosion of the pot when
it's on the stove. Wally told me he quite making them because of that
fact. The flameware body is also hard to have a glaze fit. The body
really affects the glaze. There are a couple of flameware glazes in
Ron's article.
=3D20
The article by Ron Probst that was in Studio Potter , Volume 2, (winter
1973/74many years ago is online at:
http://www.studiopotter.org/articles/?art=3D3Dart0017 ....
=3D20
Bill
mel jacobson on thu 26 may 11
i have no interest in clay flameware. but, i am happy
that others wish to work with it. good luck.
over the years i have stopped making baking dishes and
anything that has to go into the oven. it just seems that
there is risk that i no longer will take.
the world is lawsuit/ happy.
and, there are so many commercial baking products
out there. cheap at kohl's.
i don't even use my own stuff in the oven very often.
pyrex works fine.
it also has to do with a very ignorant buying public.
and, many that make food, bake, use ovens/ do not
have a clue what they are doing.
no training. and, watching the food channel does not
make a person a complete cook.
far too much left out.
so, i tell folks to serve/eat off of my dishes, pots, but cooking
is no longer what i teach. i tell them to warm food
before serving...but, care must be taken.
many have no clue about freezer to oven concepts.
clueless.
so, i can sell all i make. do not have to get into the
cooking business. i do not lose sales.
they buy what i make...and folks do not even ask
about cooking casseroles with big covers any longer. they do not
miss them.....and that is because few would ever use them.
much less a `soup tureen`.
even for a good `you betcha` nice Lutheran church casserole `hot dish`,
with four layers of canned tuna, noddles and cheese/wiz and mushroom soup
and peas.
(campbell's soup of course, no cheap subs.)
mel
the new dog goes to `hunting school` for two weeks in june.
phew, about time. she is a retrieving maniac. we had a pair coyotes
in the yard last week, and the fox is really in panic over being chased
by saffron. the critters don't like the great big golden dog, and she rule=
s
her yard inside her electronic fence. (three acres.) and we have at least
four pair of ducks nesting, with one pair of canada geese in our far back
yard. the result of lots of rain. (small lake has formed.)
from: minnetonka, mn
website: http://www.visi.com/~melpots/
clayart link: http://www.visi.com/~melpots/clayart.html
new book: http://www.21stcenturykilns.com
alternate: melpots7575@gmail.com
Bill Merrill on tue 24 apr 12
I have made hundreds of casseroles over the past 45 years and I have
never had one break. I have used the same basic clay body with some
modifications over the years due to some clay's aren't mined any more.
I have used Talc as a flux in my clay body as the MGO in the Talc helps
develop the orange color I like and the fact that Talc is helpful with
the coefficient of expansion of the clay. The body is vitreous and my
glazes work well on it. Buying clay premade is potentially
uncontrollable and you have to live with the results. I always have
mixed my clay and get what I want from the body. The body I like is
short at first and throws or hand builds well. My clay has 6 different
clay's plus Talc and grog. I call it the 'Ol rubber body because it
responds so well to the fire. If I had to buy a commercial body for
oven ware I would do all kinds of controlled tests with the body and the
glazes I would choose to use. =3D20
Wally Schwabb made great Flameware tea pots for many years. The
Spodumene changed and some of his teapots blew up on the stove so he
quit making them. He always replaced them without question,
discontinued making them. =3D20
Flameware glazes are another issue that needs tobe addressed when making
flameware. Traditional cone 10 glazes need to be adjusted drastically
to work with the body. Most of the flameware glazes I have seen are
rather muddy due to the clay body. There is an article on Flameware by
Ron Probst in Studio Potters from the 70's. It can be viewed at
http://www.studiopotter.org/articles/?art=3D3Dart0017
Keep making pots, the best are yet to be done.
Bill
ronroy@CA.INTER.NET on thu 26 apr 12
Hi Bill,
My offer to do a dilatometer test of your clay body still stands.
I would advise anyone who wants to make high fired ovenware to read
the article by Peter Sohngen - you can see it on the studio potters
web site. It explains what you need to do to make sure your clay body
does not have a damaging high expansion rate which can lead to
premature failure of ovenware.
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
RR
Quoting Bill Merrill :
> I have made hundreds of casseroles over the past 45 years and I have
> never had one break. I have used the same basic clay body with some
> modifications over the years due to some clay's aren't mined any more.
> I have used Talc as a flux in my clay body as the MGO in the Talc helps
> develop the orange color I like and the fact that Talc is helpful with
> the coefficient of expansion of the clay. The body is vitreous and my
> glazes work well on it. Buying clay premade is potentially
> uncontrollable and you have to live with the results. I always have
> mixed my clay and get what I want from the body. The body I like is
> short at first and throws or hand builds well. My clay has 6 different
> clay's plus Talc and grog. I call it the 'Ol rubber body because it
> responds so well to the fire. If I had to buy a commercial body for
> oven ware I would do all kinds of controlled tests with the body and the
> glazes I would choose to use.
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