Peter Jones on mon 10 jan 00
HI, Folks: I am new to the Clayart symposium but have been a potter for 28
years. I was just reviewing the archives on clay bodies and thought I would
share my own formula for stoneware clay that I've been developing over the
years, especially since a number of people have been requesting clay bodies
that they can mix themselves.
This clay body was developed for a number of different purposes and effects.
It had to throw smoothly and easily, be capable of making tall, thin
pieces, have good glaze fit, thermal resistance, clean firing (minimal
sulfur), minimal spotting in reduction firing, readily available
ingredients, good warm toasty color, etc, etc. You know the type. In any
case, I am very pleased with what I have come up with. It meets all those
requirements and adds a few more to boot. I can throw it the day after I
mix it and stick a pot in the bisque firing while it is still leather hard
without detriment. It's smooth and easy on my hands, fits all the glazes
beautifully, has great thermal shock resistance and that warm, toasty color
that reduction firing produces. My only complaint is that the bread dough
mixer I've been using for the past 26 years only mixes about 100 pounds at a
time. I'm getting to the point now where I feel that I would like to
subcontract the mixing out to a reputable firm who won't turn it over to
some kid who could care less about quality.
So.......
Roseville Stoneware Clay 50 lbs
Hawthorne Bonding Clay 3
Sagger Ball Clay 5
G 200 Feldspar 1
Wollastonite 2
100 mesh Mullite 2
50 mesh Grog (Christy Minerals) 3
Bentonite 1
Spanish Red Iron Oxide 150 gms
Roseville is mined by Cedar Heights Clay Co, the same one that manufactures
Goldart. It is far lower in sulfur content overall and in iron pyrites in
particular, the material that causes so much spotting in reduction. It's
about $15 more per ton than Goldart, but well worth the cost. It has much
of the same plasticity that Goldart has. Wollastonite is a calcium silicate
that adds the strength of silica, but is already bonded to calcium as a
fluxing agent. Mullite is calcined kyanite and adds tremendous strength and
good thermal expansion properties to the clay body. The grog is fine meshed
enough not to be rough on the hands nor leave trimming tracks behind, yet
adds tooth and body to the clay for larger pieces. The feldspar bonds to
any remaining free silica, the bentonite adds plasticity and makes it
readily usable right after mixing (since it needs no aging to produce
plasticity) and the iron oxide gives it color.
I mix in the water more by feel than measurement. It's best to add just a
wee bit more water than you might want to throw it with and allow it to age
for a few days before throwing. On the rare occasions when I've added too
much water, I keep a large bag of bone dry trimming scraps handy and throw
in as much as it seems necessary to dry it out. With a day or two of aging,
the excess water has been absorbed by the trimming scraps which are already
the same composition as the clay body, so there's no need to alter the
formula by adding more of one ingredient to dry it out.
A light to medium reduction produces a very nice warm, toasty brown color
that reacts very well with glazes. As I fire to cone 11 most of the time,
I've had to change some of my glazes by adding about 1% flint over the
normal cone 9 formula, but the fit seems to be ideal to the clay body as a
result. My platters, for example, have a flat, uglazed expanse across the
bottom of about 12 inches and I've never had one crack because of glaze
compression problems.
If anyone is interested in more information or a photo of the fired results,
please contact me at: pjcaver@mint.net . Good luck with it.
Peter Jones
80 Mountain Street
Camden, Maine 04843
David W McDonald on thu 13 jan 00
Hi Peter,
Thanks for sharing your stoneware body formula with us. It sounds
great, and I can't wait to try it! Gotta find a source out this way
though (Arizona) for the Roseville stoneware clay.
I'm ready to take the opposite action that you're contemplating.
After nearly 20 years of trusting someone else to mix my clay for me
(Laguna Clay Company), and becoming totally out of touch with that
process (mixing AND formulating), I'm ready to look into mixing my own
again at some point here. This after receiving several orders (tons) of
badly formulated and mixed clay last year which cost me dearly in time,
energy, MONEY, and faith. Not just faith in my clay supplier, but also
that of my customers who were counting on me to deliver on time as
promised. But I'm sure you are well aware of the risks in this arena. And
from what I've gathered, there are some truly fine and conscientious clay
companies out there, especially on your side of the continent.
Thanks again for your contribution. David McDonald
On Mon, 10 Jan 2000 16:07:31 EST Peter Jones writes:
>----------------------------Original
>message----------------------------
>HI, Folks: I am new to the Clayart symposium but have been a potter
>for 28
>years. I was just reviewing the archives on clay bodies and thought I
>would
>share my own formula for stoneware clay that I've been developing over
>the
>years, especially since a number of people have been requesting clay
>bodies
>that they can mix themselves.
>
>This clay body was developed for a number of different purposes and
>effects.
> It had to throw smoothly and easily, be capable of making tall, thin
>pieces, have good glaze fit, thermal resistance, clean firing (minimal
>sulfur), minimal spotting in reduction firing, readily available
>ingredients, good warm toasty color, etc, etc. You know the type. In
>any
>case, I am very pleased with what I have come up with. It meets all
>those
>requirements and adds a few more to boot. I can throw it the day
>after I
>mix it and stick a pot in the bisque firing while it is still leather
>hard
>without detriment. It's smooth and easy on my hands, fits all the
>glazes
>beautifully, has great thermal shock resistance and that warm, toasty
>color
>that reduction firing produces. My only complaint is that the bread
>dough
>mixer I've been using for the past 26 years only mixes about 100
>pounds at a
>time. I'm getting to the point now where I feel that I would like to
>subcontract the mixing out to a reputable firm who won't turn it over
>to
>some kid who could care less about quality.
>
>So.......
>
>Roseville Stoneware Clay 50 lbs
>Hawthorne Bonding Clay 3
>Sagger Ball Clay 5
>G 200 Feldspar 1
>Wollastonite 2
>100 mesh Mullite 2
>50 mesh Grog (Christy Minerals) 3
>Bentonite 1
>Spanish Red Iron Oxide 150 gms
>
>
>Roseville is mined by Cedar Heights Clay Co, the same one that
>manufactures
>Goldart. It is far lower in sulfur content overall and in iron
>pyrites in
>particular, the material that causes so much spotting in reduction.
>It's
>about $15 more per ton than Goldart, but well worth the cost. It has
>much
>of the same plasticity that Goldart has. Wollastonite is a calcium
>silicate
>that adds the strength of silica, but is already bonded to calcium as
>a
>fluxing agent. Mullite is calcined kyanite and adds tremendous
>strength and
>good thermal expansion properties to the clay body. The grog is fine
>meshed
>enough not to be rough on the hands nor leave trimming tracks behind,
>yet
>adds tooth and body to the clay for larger pieces. The feldspar bonds
>to
>any remaining free silica, the bentonite adds plasticity and makes it
>readily usable right after mixing (since it needs no aging to produce
>plasticity) and the iron oxide gives it color.
>
>I mix in the water more by feel than measurement. It's best to add
>just a
>wee bit more water than you might want to throw it with and allow it
>to age
>for a few days before throwing. On the rare occasions when I've added
>too
>much water, I keep a large bag of bone dry trimming scraps handy and
>throw
>in as much as it seems necessary to dry it out. With a day or two of
>aging,
>the excess water has been absorbed by the trimming scraps which are
>already
>the same composition as the clay body, so there's no need to alter the
>formula by adding more of one ingredient to dry it out.
>
>A light to medium reduction produces a very nice warm, toasty brown
>color
>that reacts very well with glazes. As I fire to cone 11 most of the
>time,
>I've had to change some of my glazes by adding about 1% flint over the
>normal cone 9 formula, but the fit seems to be ideal to the clay body
>as a
>result. My platters, for example, have a flat, uglazed expanse across
>the
>bottom of about 12 inches and I've never had one crack because of
>glaze
>compression problems.
>
>If anyone is interested in more information or a photo of the fired
>results,
>please contact me at: pjcaver@mint.net . Good luck with it.
>
>Peter Jones
>80 Mountain Street
>Camden, Maine 04843
________________________________________________________________
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Ron Roy on tue 18 jan 00
A word of warning about this clay recipe - this is the kind of body that
looks like it might generate considerable cristobalite in certain kinds of
firing.
High expansion glazes will probably do all right - but this is not the
ideal kind of body for making anything that goes into ovens
I would advise careful testing with your glazes - low expansion glazes will
be the one to pay the most attention to. If you need to know how to test
just let me know - the fist step is glazing the inside only of some fair
sized cylinders (say at least 6" high and 3" wide. After firing - if still
in one piece - freeze em and then pour in boiling water while still frozen
- do it in a sink in case they crack.
Just remember - all gazes have a different expansion/contraction rate - as
do all bodies - mix and match if you must but test for fit for all
combinations.
If you want to know if there is cristobalite in a body after firing - I'll
tell you - you have to prepare a sample and I will run it through my
dilatometer (normal cost is $100 Canadian) and you will be able to see if
there is any.
Look for an excelent article on this subject (cristobalite in stoneware
bodies) in the current issue of studio potter - by Peter Sohngen. The
dilatometer work was done by me and there will be lots of graphs to look at
- and you will see what a cristobalite and quartz curve looks like.
RR
High expansion glazes will probably do all right - but this is not the
ideal kind of body for making anything that goes into ovens
>>Roseville Stoneware Clay 50 lbs
>>Hawthorne Bonding Clay 3
>>Sagger Ball Clay 5
>>G 200 Feldspar 1
>>Wollastonite 2
>>100 mesh Mullite 2
>>50 mesh Grog (Christy Minerals) 3
>>Bentonite 1
>>Spanish Red Iron Oxide 150 gms
>>
>>
>>Roseville is mined by Cedar Heights Clay Co, the same one that
>>manufactures
>>Goldart. It is far lower in sulfur content overall and in iron
>>pyrites in
>>particular, the material that causes so much spotting in reduction.
>>It's
>>about $15 more per ton than Goldart, but well worth the cost. It has
>>much
>>of the same plasticity that Goldart has. Wollastonite is a calcium
>>silicate
>>that adds the strength of silica, but is already bonded to calcium as
>>a
>>fluxing agent. Mullite is calcined kyanite and adds tremendous
>>strength and
>>good thermal expansion properties to the clay body. The grog is fine
>>meshed
>>enough not to be rough on the hands nor leave trimming tracks behind,
>>yet
>>adds tooth and body to the clay for larger pieces. The feldspar bonds
>>to
>>any remaining free silica, the bentonite adds plasticity and makes it
>>readily usable right after mixing (since it needs no aging to produce
>>plasticity) and the iron oxide gives it color.
>>
>>I mix in the water more by feel than measurement. It's best to add
>>just a
>>wee bit more water than you might want to throw it with and allow it
>>to age
>>for a few days before throwing. On the rare occasions when I've added
>>too
>>much water, I keep a large bag of bone dry trimming scraps handy and
>>throw
>>in as much as it seems necessary to dry it out. With a day or two of
>>aging,
>>the excess water has been absorbed by the trimming scraps which are
>>already
>>the same composition as the clay body, so there's no need to alter the
>>formula by adding more of one ingredient to dry it out.
>>
>>A light to medium reduction produces a very nice warm, toasty brown
>>color
>>that reacts very well with glazes. As I fire to cone 11 most of the
>>time,
>>I've had to change some of my glazes by adding about 1% flint over the
>>normal cone 9 formula, but the fit seems to be ideal to the clay body
>>as a
>>result. My platters, for example, have a flat, uglazed expanse across
>>the
>>bottom of about 12 inches and I've never had one crack because of
>>glaze
>>compression problems.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Mark Mondloch on wed 19 jan 00
Ron,
What is it about this recipe that makes you say it might generate lots of
cristobalite?- the relatively low percent of feldspar?
Sylvia
Ron Roy wrote:
> ----------------------------Original message----------------------------
> A word of warning about this clay recipe - this is the kind of body that
> looks like it might generate considerable cristobalite in certain kinds of
> firing.
>
> High expansion glazes will probably do all right - but this is not the
> ideal kind of body for making anything that goes into ovens
>
> I would advise careful testing with your glazes - low expansion glazes will
> be the one to pay the most attention to. If you need to know how to test
> just let me know - the fist step is glazing the inside only of some fair
> sized cylinders (say at least 6" high and 3" wide. After firing - if still
> in one piece - freeze em and then pour in boiling water while still frozen
> - do it in a sink in case they crack.
>
> Just remember - all gazes have a different expansion/contraction rate - as
> do all bodies - mix and match if you must but test for fit for all
> combinations.
>
> If you want to know if there is cristobalite in a body after firing - I'll
> tell you - you have to prepare a sample and I will run it through my
> dilatometer (normal cost is $100 Canadian) and you will be able to see if
> there is any.
>
> Look for an excelent article on this subject (cristobalite in stoneware
> bodies) in the current issue of studio potter - by Peter Sohngen. The
> dilatometer work was done by me and there will be lots of graphs to look at
> - and you will see what a cristobalite and quartz curve looks like.
>
> RR
>
> High expansion glazes will probably do all right - but this is not the
> ideal kind of body for making anything that goes into ovens
> >>Roseville Stoneware Clay 50 lbs
> >>Hawthorne Bonding Clay 3
> >>Sagger Ball Clay 5
> >>G 200 Feldspar 1
> >>Wollastonite 2
> >>100 mesh Mullite 2
> >>50 mesh Grog (Christy Minerals) 3
> >>Bentonite 1
> >>Spanish Red Iron Oxide 150 gms
> >>
> >>
> >>Roseville is mined by Cedar Heights Clay Co, the same one that
> >>manufactures
> >>Goldart. It is far lower in sulfur content overall and in iron
> >>pyrites in
> >>particular, the material that causes so much spotting in reduction.
> >>It's
> >>about $15 more per ton than Goldart, but well worth the cost. It has
> >>much
> >>of the same plasticity that Goldart has. Wollastonite is a calcium
> >>silicate
> >>that adds the strength of silica, but is already bonded to calcium as
> >>a
> >>fluxing agent. Mullite is calcined kyanite and adds tremendous
> >>strength and
> >>good thermal expansion properties to the clay body. The grog is fine
> >>meshed
> >>enough not to be rough on the hands nor leave trimming tracks behind,
> >>yet
> >>adds tooth and body to the clay for larger pieces. The feldspar bonds
> >>to
> >>any remaining free silica, the bentonite adds plasticity and makes it
> >>readily usable right after mixing (since it needs no aging to produce
> >>plasticity) and the iron oxide gives it color.
> >>
> >>I mix in the water more by feel than measurement. It's best to add
> >>just a
> >>wee bit more water than you might want to throw it with and allow it
> >>to age
> >>for a few days before throwing. On the rare occasions when I've added
> >>too
> >>much water, I keep a large bag of bone dry trimming scraps handy and
> >>throw
> >>in as much as it seems necessary to dry it out. With a day or two of
> >>aging,
> >>the excess water has been absorbed by the trimming scraps which are
> >>already
> >>the same composition as the clay body, so there's no need to alter the
> >>formula by adding more of one ingredient to dry it out.
> >>
> >>A light to medium reduction produces a very nice warm, toasty brown
> >>color
> >>that reacts very well with glazes. As I fire to cone 11 most of the
> >>time,
> >>I've had to change some of my glazes by adding about 1% flint over the
> >>normal cone 9 formula, but the fit seems to be ideal to the clay body
> >>as a
> >>result. My platters, for example, have a flat, uglazed expanse across
> >>the
> >>bottom of about 12 inches and I've never had one crack because of
> >>glaze
> >>compression problems.
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough
> Ontario, Canada
> M1G 3N8
> Evenings 416-439-2621
> Fax 416-438-7849
--
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake, WI 53075
silvercreek@execpc.com
http://www.execpc.com/silvercreek
Ron Roy on thu 20 jan 00
Hi Sylvia,
I'm going to try to keep this short - but you are essentially right - KNaO
are the oxides that will melt cristobalite as it forms - CaO and MgO don't
do it well at all. On top of this the body has iron oxide which is a big
time flux in reduction but has the reputation of being a catalyst for
cristobalite formation. I think it has more to do with - if the iron is
fluxing the body you can't have as much KNaO.
I know there is no silica added to the body below but the fireclays and
ball clays will have free silica with them. When making a body for oven use
it is best to not include any free silica - I should say fine silica -
granular does not seem to be a problem. It's the micro fine silica - of
which there is a lot even in 200m silica - like over 90 % over 400 mesh and
finer.
The problem becomes - having a refractory enough body to take at least 10%
feldspar.
I have measured any number of cone 10 porcelains (they usually have about
25% pot spar and 25% silica and have never seen any cristobalite in any of
them.
There is usually at least some in every cone 10 reduction body I have
measured - as I have said - Peter Sohngen has really nailed this in his
article - I don't have a copy of Studio Potter yet but I'm sure it will
arrive any day now.
RR
>----------------------------Original message----------------------------
>Ron,
>What is it about this recipe that makes you say it might generate lots of
>cristobalite?- the relatively low percent of feldspar?
>Sylvia
>
>Ron Roy wrote:
>
>> ----------------------------Original message----------------------------
>> A word of warning about this clay recipe - this is the kind of body that
>> looks like it might generate considerable cristobalite in certain kinds of
>> firing.
>>
>> High expansion glazes will probably do all right - but this is not the
>> ideal kind of body for making anything that goes into ovens
>>
>> I would advise careful testing with your glazes - low expansion glazes will
>> be the one to pay the most attention to. If you need to know how to test
>> just let me know - the fist step is glazing the inside only of some fair
>> sized cylinders (say at least 6" high and 3" wide. After firing - if still
>> in one piece - freeze em and then pour in boiling water while still frozen
>> - do it in a sink in case they crack.
>>
>> Just remember - all gazes have a different expansion/contraction rate - as
>> do all bodies - mix and match if you must but test for fit for all
>> combinations.
>>
>> If you want to know if there is cristobalite in a body after firing - I'll
>> tell you - you have to prepare a sample and I will run it through my
>> dilatometer (normal cost is $100 Canadian) and you will be able to see if
>> there is any.
>>
>> Look for an excelent article on this subject (cristobalite in stoneware
>> bodies) in the current issue of studio potter - by Peter Sohngen. The
>> dilatometer work was done by me and there will be lots of graphs to look at
>> - and you will see what a cristobalite and quartz curve looks like.
>>
>> RR
>>
>> High expansion glazes will probably do all right - but this is not the
>> ideal kind of body for making anything that goes into ovens
>> >>Roseville Stoneware Clay 50 lbs
>> >>Hawthorne Bonding Clay 3
>> >>Sagger Ball Clay 5
>> >>G 200 Feldspar 1
>> >>Wollastonite 2
>> >>100 mesh Mullite 2
>> >>50 mesh Grog (Christy Minerals) 3
>> >>Bentonite 1
>> >>Spanish Red Iron Oxide 150 gms
>> >>
>> >>
>> >>Roseville is mined by Cedar Heights Clay Co, the same one that
>> >>manufactures
>> >>Goldart. It is far lower in sulfur content overall and in iron
>> >>pyrites in
>> >>particular, the material that causes so much spotting in reduction.
>> >>It's
>> >>about $15 more per ton than Goldart, but well worth the cost. It has
>> >>much
>> >>of the same plasticity that Goldart has. Wollastonite is a calcium
>> >>silicate
>> >>that adds the strength of silica, but is already bonded to calcium as
>> >>a
>> >>fluxing agent. Mullite is calcined kyanite and adds tremendous
>> >>strength and
>> >>good thermal expansion properties to the clay body. The grog is fine
>> >>meshed
>> >>enough not to be rough on the hands nor leave trimming tracks behind,
>> >>yet
>> >>adds tooth and body to the clay for larger pieces. The feldspar bonds
>> >>to
>> >>any remaining free silica, the bentonite adds plasticity and makes it
>> >>readily usable right after mixing (since it needs no aging to produce
>> >>plasticity) and the iron oxide gives it color.
>> >>
>> >>I mix in the water more by feel than measurement. It's best to add
>> >>just a
>> >>wee bit more water than you might want to throw it with and allow it
>> >>to age
>> >>for a few days before throwing. On the rare occasions when I've added
>> >>too
>> >>much water, I keep a large bag of bone dry trimming scraps handy and
>> >>throw
>> >>in as much as it seems necessary to dry it out. With a day or two of
>> >>aging,
>> >>the excess water has been absorbed by the trimming scraps which are
>> >>already
>> >>the same composition as the clay body, so there's no need to alter the
>> >>formula by adding more of one ingredient to dry it out.
>> >>
>> >>A light to medium reduction produces a very nice warm, toasty brown
>> >>color
>> >>that reacts very well with glazes. As I fire to cone 11 most of the
>> >>time,
>> >>I've had to change some of my glazes by adding about 1% flint over the
>> >>normal cone 9 formula, but the fit seems to be ideal to the clay body
>> >>as a
>> >>result. My platters, for example, have a flat, uglazed expanse across
>> >>the
>> >>bottom of about 12 inches and I've never had one crack because of
>> >>glaze
>> >>compression problems.
>>
>> Ron Roy
>> 93 Pegasus Trail
>> Scarborough
>> Ontario, Canada
>> M1G 3N8
>> Evenings 416-439-2621
>> Fax 416-438-7849
>
>--
>Mark & Sylvia Mondloch
>Silver Creek Pottery & Forge
>W6725 Hwy 144
>Random Lake, WI 53075
>
>silvercreek@execpc.com
>http://www.execpc.com/silvercreek
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Peter Jones on fri 21 jan 00
I don't necessarily disagree with Ron Roy's comments on my clay body formula
other than to say that it works for me. I've had no problems with it so far
and I've been using it for a number of years, making casseroles and large,
flat bottom platters (no glaze on the bottom expanse) with a number of
different glazes on them. Teapots, too. As a potter who uses a lot of his
own wares in his own house, I can be pretty cavalier about how I treat my
own work. The only breakage I've experienced in normal usage has been when
I drop it on the floor. But I'm working on that, too! In any case, my wife
routinely pours boiling hot water into a cold teapot in the morning and it
has yet to crack or even ping. I've been using the casserole for probably
10 years, about twice a month on average. I've yet to have any customers
come back to me complaining about how their casserole has failed. Of course
I do suggest to people who buy my work that they place their casserole in a
cold oven and then turn it on.
Perhaps the clay body could use a small increase in the feldspar content.
Even 1% more would double the amount without appreciably altering its
throwing quality. It surely wouldn't hurt the reaction with the glazes
either, perhaps even improving them. But, this body has gone through many
changes over the years and it's hard to argue with success. In fact there
used to be flint thrown in and more feldspar as well.
In any case, I don't know that there is any one ideal clay body formula.
This one works extremely well for me with the glazes I use and has caused me
no grief. Hard to argue with that.
Peter Jones
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