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mixing clays

updated mon 20 feb 12

 

Gail Dapogny on tue 6 jun 00


Ron, this question is really for you although I certainly welcome
anyone who would be interested and generous enough to respond:


Do you think there would be any bad consequences with combining (dry
mixing) white stoneware and porcelain bodies, then wet mixing and
pugging them?

The porcelain body is as follows (using our batch amounts):


ANN ARBOR PORCELAIN:

Grolleg 68

Custer 180

EPK 92

6-Tile 60

OM-4 28

Flint 52

Bentonite 8

TOTAL 408


The white stoneware body is:

WHITE STONEWARE BODY (Ann Arbor):

Fire Clay (AP Green) 31

OM-4 Ball 14

Custer Spar 14

6 Tile 22

Flint (140 mesh) 9

Fine Grog 8

Bentonite 2

TOTAL 100


Ron, I know you must be scratching your head and wondering why I
wouldn't just ask you about reformulating (and I might yet). Right
now, we're on a pretty tight schedule getting ready for the AA Art Fair
and I can't really interrupt our guild's clay making schedule to fool
around with a new recipe for my own benefit. But I'm sick of the
graininess of the white stoneware and would like to try to smooth it
out a bit, but retain the stoneware strength. I could accomplish
this, I think, by combining them (although I don't have any idea of
what proportions I should use----50/50?) or instead by adding some
porcelain scrap instead of stoneware scrap to the stonewarebatch when I
am mixing/pugging it. Any thoughts? Can you give meany
advice?

Thanks....Gail








Gail Dapogny

1154 Olden Road

Ann Arbor, MI 48103-3005

(734) 665-9816

gdapogny@umich.edu

www.silverhawk.com/ex99/dapogny

douglas gray on thu 8 jun 00


Gail,

I'd hold out to hear from Ron, but from my experience I'd have to say
Yes, you can mix the two clay bodies together. Dry mixing will give you the
most consistent mix, but I've carefully wedged wet clay bodies together and used
them. I don't know where the name came from, but I've always called those
mixtures of stoneware and porcelain BUCKWHEAT. I've done half and half
mixtures, one third to two thirds. There really aren't any steadfast rules
except that all the part of the clay form should be made out of the same
mixture--meaning that lids and handles and sprigs of decoration should be made
from the same mixture to minimize shrinkage and drying stresses.

Now the disclaimer. Mixing the clay bodies will result in a smooth, less
gritty, clay body but you will also be changing the shrinkage rate of the clays.
Shrinkange will be slightly more than the stoneware alone and slightly less than
the porcelain. This means that glazes that perfectly fit either the stoneware
or porcelain most likely will not perfectly fit the mixture--that is to say you
might notice more or less crazing, or worse more or less cracking of the clay.
Now, it could be that the shrinkage rate of your white stoneware is close to the
rate for porcelain, in which case the fit issue would be minimal.

You will also notice slight color and surface changes in the fired glazes. If
you are used to seeing the glazes on porcelain, the addition of white stoneware
with probably tend to muddy the color and make the glaze less glassy. This is
due to increased amounts of trace iron and refractory clays used to make
stoneware. If on the other hand you've been using the glazes on stoneware
alone, you will notice that the colors may be a bit brighter, more glassy, and
may tend to run more. This is a rusult of the extra flux and glass former that
is present in porcelain.

>From experience though, I have mixed stoneware and porcelains before without
notable difficulties with the glaze. You should be able to test your mixture
and glazes without interupting the rest of your studio mates.

Doug

In message Gail Dapogny writes:
> Ron, this question is really for you although I certainly welcome
> anyone who would be interested and generous enough to respond:
>
>
> Do you think there would be any bad consequences with combining (dry
> mixing) white stoneware and porcelain bodies, then wet mixing and
> pugging them?


Douglas E. Gray, Assistant Professor of Art
P.O. Box 100547
Department of Fine Arts and Mass Communication
Francis Marion University
Florence, South Carolina 29501-0547

dgray@fmarion.edu
phone 843/661-1535
fax 843/661-1432

Ron Roy on fri 9 jun 00


Hi Gail,

I look after a few bodies that are mixtures (50/50) of porcelain and
stoneware. I think it will work if both bodies fire well to the temperature
you want the mixture to fire to.

If you really want to be sure - test the two you want to mix together for
absorbency - and test the mixture as well.

You want the porcelain to be close to no absorption and the stoneware to be
around 2 to 1% - the mixture will be in between the two as far as I know. I
have never seen it work any other way.

I think it's a good idea overall but - you can expect your glazes to be not
as melted as on the porcelain but the workability should improve over the
porcelain.

RR


>Ron, this question is really for you although I certainly welcome anyone
>who would be interested and generous enough to respond:
>
>Do you think there would be any bad consequences with combining (dry
>mixing) white stoneware and porcelain bodies, then wet mixing and pugging
>them?
>The porcelain body is as follows (using our batch amounts):
>
>ANN ARBOR PORCELAIN:
>Grolleg 68
>Custer 180
>EPK 92
>6-Tile 60
>OM-4 28
>Flint 52
>Bentonite 8
>TOTAL 408
>
>The white stoneware body is:
>WHITE STONEWARE BODY (Ann Arbor):
> Fire Clay (AP Green) 31
> OM-4 Ball 14
> Custer Spar 14
> 6 Tile 22
> Flint (140 mesh) 9
> Fine Grog 8
> Bentonite 2
> TOTAL 100
>
>Ron, I know you must be scratching your head and wondering why I wouldn't
>just ask you about reformulating (and I might yet). Right now, we're on a
>pretty tight schedule getting ready for the AA Art Fair and I can't really
>interrupt our guild's clay making schedule to fool around with a new
>recipe for my own benefit. But I'm sick of the graininess of the white
>stoneware and would like to try to smooth it out a bit, but retain the
>stoneware strength. I could accomplish this, I think, by combining them
>(although I don't have any idea of what proportions I should
>use----50/50?) or instead by adding some porcelain scrap instead of
>stoneware scrap to the stonewarebatch when I am mixing/pugging it. Any
>thoughts? Can you give meany advice?
>Thanks....Gail

Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849

Gail Dapogny on sun 11 jun 00


Hi Ron,
I searched the archives for clay absorbency test (also density) but nothing
appeared. How do I accomplish that?
Thanks. ---Gail



>Hi Gail,
>
>I look after a few bodies that are mixtures (50/50) of porcelain and
>stoneware. I think it will work if both bodies fire well to the temperature
>you want the mixture to fire to.
>
>If you really want to be sure - test the two you want to mix together for
>absorbency - and test the mixture as well.

Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
www.silverhawk.com/ex99/dapogny

Ben Morrison on fri 17 feb 12


I'd say with out doing absorption testing on your own you can't really know=
=3D
. The manufacturers seem to have a wide variety of ideas about what a cone =
=3D
6 clay is supposed to be. I use Clay Art in Tacoma which mixes up some nice=
=3D
clay bodies I've come to rely on. I've found that some suppliers are marki=
=3D
ng clays cone 6 - 10. This obviously won't be vitrified at cone 6, but it's=
=3D
being marketed that way. I purchase clays that are formulated 4 - 6 for co=
=3D
ne 6 ware. Meaning when I purchase Clay Art's cone 6 porcelain it's a true =
=3D
cone 6 porcelain that when fired to cone 10 is way over fired and will sag =
=3D
and bloat.=3DA0=3D0A=3D0ALong story short with out knowing the true chemist=
ry beh=3D
ind the clay you're mixing together we can't really provide any insight.=3D=
0A=3D
=3D0A-Ben=3D0A=3D0A=3D0A________________________________=3D0A From: "ronroy=
@CA.INTER.=3D
NET" =3D0ATo: Clayart@LSV.CERAMICS.ORG =3D0ASent: Frid=
ay, =3D
February 17, 2012 11:46 AM=3D0ASubject: Re: mixing clays=3D0A =3D0AHi David=
,=3D0A=3D
=3D0ADepends - lets say a cone 6 oxidation stoneware has an absorbency of=
=3D0A2=3D
% and you mix it with a cone 10 oxidation stoneware with an=3D0Aabsorbency =
of=3D
2% then the answer is yes - mixing equal amounts of each=3D0Afired to cone=
8=3D
will have an approximate absorbency. I would expect=3D0Athe shrinkage and =
ex=3D
pansion would be and average as well.=3D0A=3D0AThe only way you can tell wh=
at t=3D
he absorbency of most clays is to test=3D0Athem yourself - most clay compan=
ie=3D
s don't test their clays before=3D0Ashipping and most clay companies still =
la=3D
bel their clay bodies to be=3D0Asuitable at many different temperatures so =
yo=3D
u can't predict what will=3D0Ahappen unless you do your own testing.=3D0A=
=3D0ANot=3D
sure what to say about mixing a stoneware and a porcelain clay to=3D0Aget =
an=3D
average - many porcelains when tested have no absorbency which=3D0Acould m=
ea=3D
n they actually have more flux than they need to be mature -=3D0Athat extra=
f=3D
lux would give an unexpected result.=3D0A=3D0AIf one of the clays contained=
iro=3D
n and was fired in reduction - mixed=3D0Awith a clay that was fired in oxid=
at=3D
ion and the resulting clay was=3D0Afired in oxidation you would probably ge=
t =3D
a different result.=3D0A=3D0AIf I could see the two clay recipes and how th=
ey a=3D
re fired I could=3D0Agive a more definitive answer.=3D0A=3D0ARR=3D0A=3D0A=
=3D0AQuoting D=3D
avid Todd :=3D0A=3D0A> If I mix equal parts of a =
cone=3D
10 clay and a cone 6 clay together, is it a=3D0A> cone 8 firing clay? Woul=
d =3D
the COE be averaged as well?=3D0A> David Todd=3D0A> www.otterrafting.com=3D=
0A>

David Todd on fri 17 feb 12


If I mix equal parts of a cone 10 clay and a cone 6 clay together, is it a
cone 8 firing clay? Would the COE be averaged as well?
David Todd
www.otterrafting.com

ronroy@CA.INTER.NET on fri 17 feb 12


Hi David,

Depends - lets say a cone 6 oxidation stoneware has an absorbency of
2% and you mix it with a cone 10 oxidation stoneware with an
absorbency of 2% then the answer is yes - mixing equal amounts of each
fired to cone 8 will have an approximate absorbency. I would expect
the shrinkage and expansion would be and average as well.

The only way you can tell what the absorbency of most clays is to test
them yourself - most clay companies don't test their clays before
shipping and most clay companies still label their clay bodies to be
suitable at many different temperatures so you can't predict what will
happen unless you do your own testing.

Not sure what to say about mixing a stoneware and a porcelain clay to
get an average - many porcelains when tested have no absorbency which
could mean they actually have more flux than they need to be mature -
that extra flux would give an unexpected result.

If one of the clays contained iron and was fired in reduction - mixed
with a clay that was fired in oxidation and the resulting clay was
fired in oxidation you would probably get a different result.

If I could see the two clay recipes and how they are fired I could
give a more definitive answer.

RR


Quoting David Todd :

> If I mix equal parts of a cone 10 clay and a cone 6 clay together, is it =
a
> cone 8 firing clay? Would the COE be averaged as well?
> David Todd
> www.otterrafting.com
>

Vince Pitelka on sat 18 feb 12


Ben Morrison wrote:
"I've found that some suppliers are marking clays cone 6 - 10. This
obviously won't be vitrified at cone 6, but it's being marketed that way."

Or even worse, marketed as cone 6-11. It is important for all of us to
realize that this marketing practice is a ruse, a deception. You cannot
have a single claybody for utilitarian ware that will be properly vitrified
at both cone-6 and cone-10. If it is mature at cone-10, it will be
underfired at cone-6 and glazes will likely craze badly. If it is mature a=
t
cone 6 it will be seriously over-vitrified at Cone-10 with possible
shivering and dunting and might even bloat and sag. I wish we could all
agree to boycott any claybodies advertised as covering such a broad firing
range. If they are intended purely for sculptural work, then it isn't such
a problem, but for utilitarian work it is a marketing deception.

In answer to David's original question, I agree that if a person has a
claybody that matures properly at cone-6 and one that matures properly at
cone-10 and equal parts of the two are mixed, the resulting claybody will
mature at cone-8. That is a pretty safe assumption.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net
http://iweb.tntech.edu/wpitelka/

Steve Mills on sat 18 feb 12


I suspect the real answer is "suck it and see!"
I'm currently mixing variations of two clays, one local, one bought, in an =
e=3D
ffort to achieve a body that will look good in gas reduction, throw well, a=
n=3D
d will woodfire.=3D20
The local has real visual character in reduction, but lacks throwing streng=
t=3D
h, the bought one woodfires beautifully and throws well but is as boring as=
h=3D
ell in reduction, so trial and error is my journey at the moment.=3D20

Steve M


Steve Mills
Bath
UK
www.mudslinger.me.uk badly
Sent from my iPod


On 17 Feb 2012, at 16:54, David Todd wrote:

> If I mix equal parts of a cone 10 clay and a cone 6 clay together, is it =
a=3D

> cone 8 firing clay? Would the COE be averaged as well?
> David Todd
> www.otterrafting.com

Lee on sun 19 feb 12


All the clay mixing I saw in Japan was the combination of two or more
soft clays.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/

=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue