Michael Wendt on sun 1 nov 09
Bob,
Several people have asked me if the body I fire would work a
cone 6.
It is vitreous and translucent at cone 10 so it might still
qualify as a hard cone 6 stoneware. Why not try a box?
Regards,
Michael Wendt
wendtpottery.com
Bob wrote:
I'm having trouble finding a white or buff ^6 stoneware clay
that doesn't
change to a dirty gray in reduction: The available ^6 clay
seem to be
formulated for oxidation firing.
On the other hand, there are some ^10 clays out there that
seem to work at
mid-range. Som here's my question: Is there any practical
reason not to use
the cone 10 stuff at cone 6? I know that it won't be quite
as vitrified, but
is the difference more theoretical than real? That is, would
someone using
my pots be able to tell?
Alternatively, if someone can steer me toward a good light
colored ^6 clay
for use in reduction, I'd greatly appreciate it.
Thanks!
Bob Johnson
Bob Johnson on sun 1 nov 09
I'm having trouble finding a white or buff ^6 stoneware clay that doesn't
change to a dirty gray in reduction: The available ^6 clay seem to be
formulated for oxidation firing.
On the other hand, there are some ^10 clays out there that seem to work at
mid-range. Som here's my question: Is there any practical reason not to use
the cone 10 stuff at cone 6? I know that it won't be quite as vitrified, bu=
t
is the difference more theoretical than real? That is, would someone using
my pots be able to tell?
Alternatively, if someone can steer me toward a good light colored ^6 clay
for use in reduction, I'd greatly appreciate it.
Thanks!
Bob Johnson
Roseburg, Oregon
http://www.flickr.com/photos/psychoceramics/
Sumi von Dassow on sun 1 nov 09
Bob
I have been using cone 10 B-Mix from Laguna and firing it to cone 7 in
reduction. It doesn't stay white,
it gets a bit toasty colored, but most glazes are nice and bright on it.
I recently tested a mug for absorption and
microwavability and came up with an absorption rate of 2.2% - even
better than the absorption rate
of cone 5 B-Mix fired at cone 6 in oxidation, curiously enough - and
when microwaved empty /after/
the absorption test it didn't get hot. (put in microwave oven empty
alongside a full cup of water and
heated until the water in the full cup was hot.)
So my conclusion from this one test is that it is reasonably well
vitrified. If you are firing to cone 6
in reduction the cone 5 B-Mix is fine and whiter than the cone 10 (well,
it is gray), but I found that it
can sometimes bloat at cone 7. If you want really white, there are cone
6 porcelains available, but
you can try a cone 10 porcelain and test it for absorption.
I hope that helps, if you can get Laguna clays.
Sumi
> I'm having trouble finding a white or buff ^6 stoneware clay that doesn't
> change to a dirty gray in reduction: The available ^6 clay seem to be
> formulated for oxidation firing.
>
>
>
> On the other hand, there are some ^10 clays out there that seem to work a=
t
> mid-range. Som here's my question: Is there any practical reason not to u=
se
> the cone 10 stuff at cone 6? I know that it won't be quite as vitrified, =
but
> is the difference more theoretical than real? That is, would someone usin=
g
> my pots be able to tell?
>
>
>
> Alternatively, if someone can steer me toward a good light colored ^6 cla=
y
> for use in reduction, I'd greatly appreciate it.
>
>
>
> Thanks!
>
>
>
> Bob Johnson
> Roseburg, Oregon
> http://www.flickr.com/photos/psychoceramics/
>
>
>
Veena Raghavan on sun 1 nov 09
Bob,
Have you tried Highwater's P5, which is a cone 6 porcelaneous clay. It is
pretty white.
Laguna has a white porcelain called Frost, which is very white and
translucent.
Veena
In a message dated 11/1/2009 10:32:16 PM Eastern Standard Time,
sumi@HERWHEEL.COM writes:
>
> >
> >Alternatively, if someone can steer me toward a good light colored ^6
> clay
> >for use in reduction, I'd greatly appreciate it.
> >
> >
> >
> >Thanks!
> >
> >
> >
> >Bob Johnson
> >Roseburg, Oregon
> >http://www.flickr.com/photos/psychoceramics/
> >
> >
> >
VeenaRaghavan@cs.com
Fred Parker on mon 2 nov 09
Bob:
I am currently testing Highwater's "Helios" porcelain. It has a very wid=
=3D
e
firing range from ^6 to ^11 and can be fired to a very nice white in eith=
=3D
er
oxidation or reduction, according to the company. As I said, I am testin=
=3D
g
some now in electric oxidation at ^6. Will have the result tomorrow. Wh=
=3D
at
I can say about it so far is that it has been great up to this point. It=
=3D
throws very nicely -- much like "B" mix -- and it dries well. I had no
cracking problem and dried it about the same rate as I dry white stonewar=
=3D
e.
Fred Parker
On Sun, 1 Nov 2009 11:54:11 -0800, Bob Johnson wrot=
=3D
e:
SNIP
>
>Alternatively, if someone can steer me toward a good light colored ^6 cl=
=3D
ay
>for use in reduction, I'd greatly appreciate it.
>
John Britt on mon 2 nov 09
Jeff,
I am pretty sure the Helios is now rated cone 7 - 10, not 6 - 10, but I c=
=3D
ould=3D20
be wrong. That is with the less than 1% absorption,
John Britt
www.johnbrittpottery.com
Lee Love on mon 2 nov 09
Bob, can you get a with earthenware? It is the next thing I will
test. I have been having good luck with Continental Clay's smooth
red earthenware. Look at Linda Arbuckle's pdf handouts for glazes.
--
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Chaeli Sullivan on mon 2 nov 09
Hi Bob
I've long been impressed with Georgie's: Gmix-6 with grog.=3DA0 Used it in =
ox=3D
idation and reduction and it stays white.=3DA0 Plus, it's an extremely vers=
at=3D
ile clay.
Good luck
Chae
Bob wrote:
I'm having trouble finding a white or buff ^6 stoneware clay that doesn't c=
=3D
hange to a dirty gray in reduction: The available ^6 clay seem to be formul=
=3D
ated for oxidation firing.
Alternatively, if someone can steer me toward a good light colored ^6 clay =
=3D
for use in reduction, I'd greatly appreciate it.
Thanks!
Bob Johnson
=3D0A=3D0A=3D0A
John Hesselberth on mon 2 nov 09
On Nov 2, 2009, at 8:15 AM, Fred Parker wrote:
> It has a very wide
> firing range from ^6 to ^11 and can be fired to a very nice white in
> either
> oxidation or reduction, according to the company.
Hi Fred and others following this thread.
Be aware that NO clay body I have ever seen is suitable for all
purposes over a 5 cone firing range. Of particular concern is the
degree of vitrification for functional work. A body designed for cone
10/11 may well leak at cone 6. You cannot depend on the glaze to
prevent leaking.
A body designed for cone 6 may well be overfired and slump or be too
brittle at cone 10/11. Clay bodies normally only have a couple cone
range for a particular use. In my opinion, the clay body manufacturers
do a great disservice when they rate a body with a 5 cone range
without some better definition of what they mean.
Alway check water absorption yourself if you are doing functional
work. It should be less than 3%--my own preference is 1.5-2%. Clay
body manufacturers have their own idea of what the standards should be
for their body. In addition very few check every batch for meeting
those standards and they do vary. For example I had a batch of cone 5
B mix a few years back that leaked at cone 6 but was OK at cone 7. It
may have been an oddball, but it happened. Fortunately, I checked it
and caught it before I put pots out on the market with that batch.
By the way, another good and easy check for leakers is to fill a
glazed and fired pot with water and set it on a paper towel overnight.
The paper towel will tell the story in the morning.
Regards,
John
Bob Johnson on mon 2 nov 09
Lee: I really need to stay with ^6 stoneware or porcelain, because =3D
that's
what all my glazes are suited for. Also, I would like to find a light =3D
white,
cream, or buff body to brighten things up. The problem is that most of =3D
them
turn a not-so-pretty gray in reduction. I may have to go to a true
porcelain, although I don't want the hassle of cracking problems.
Thanks!
Bob
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Lee Love
Sent: Monday, November 02, 2009 6:39 AM
To: Clayart@LSV.CERAMICS.ORG
Subject: Re: Cone 10 clay at cone 6: How much difference?
Bob, can you get a with earthenware? It is the next thing I will
test. I have been having good luck with Continental Clay's smooth
red earthenware. Look at Linda Arbuckle's pdf handouts for glazes.
--
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
No virus found in this incoming message.
Checked by AVG - www.avg.com=3D20
Version: 8.5.424 / Virus Database: 270.14.45/2476 - Release Date: =3D
11/02/09
07:51:00
Sumi von Dassow on tue 3 nov 09
Bob
The absorbency test is to take a fired piece warm from the kiln and
weigh it accurately on a gram scale;
then immerse it in water, bring it to a boil, boil 5 minutes; let it
cool down in the water; dry it off with a lint-free
cloth, and weigh it again. Subtract the dry weight from the wet weight,
divide the difference by the dry weight,
and multiply by 100. That is your absorbency percentage. Vitrified clay
has an absorbency of no more than
about 3%.
Sumi
> Thanks, Sumi (and others who made similar suggestions). I did try the Lag=
una
> ^5 B mix, but didn't like the gray I got in reduction; haven't tried the =
^10
> version.
>
> Currently I'm working with some Georgie's ^10 Deschutes White for a Steve=
n
> Hill workshop coming up next week--but I'll also try it in my kiln at ^6 =
in
> reduction. If it works well, I'll let you know.
>
> Can anyone tell me a good way to find out how vitrified the clay is?
> Absorbency? Ringing? Etc.?
>
> Bob
>
>
Bob Johnson on tue 3 nov 09
Thanks, Sumi (and others who made similar suggestions). I did try the Lagun=
a
^5 B mix, but didn't like the gray I got in reduction; haven't tried the ^1=
0
version.
Currently I'm working with some Georgie's ^10 Deschutes White for a Steven
Hill workshop coming up next week--but I'll also try it in my kiln at ^6 in
reduction. If it works well, I'll let you know.
Can anyone tell me a good way to find out how vitrified the clay is?
Absorbency? Ringing? Etc.?
Bob
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Sumi von Dasso=
w
Sent: Sunday, November 01, 2009 4:42 PM
To: Clayart@LSV.CERAMICS.ORG
Subject: Re: Cone 10 clay at cone 6: How much difference?
Bob
I have been using cone 10 B-Mix from Laguna and firing it to cone 7 in
reduction. It doesn't stay white,
it gets a bit toasty colored, but most glazes are nice and bright on it.
I recently tested a mug for absorption and
microwavability and came up with an absorption rate of 2.2% - even
better than the absorption rate
of cone 5 B-Mix fired at cone 6 in oxidation, curiously enough - and
when microwaved empty /after/
the absorption test it didn't get hot. (put in microwave oven empty
alongside a full cup of water and
heated until the water in the full cup was hot.)
So my conclusion from this one test is that it is reasonably well
vitrified. If you are firing to cone 6
in reduction the cone 5 B-Mix is fine and whiter than the cone 10 (well,
it is gray), but I found that it
can sometimes bloat at cone 7. If you want really white, there are cone
6 porcelains available, but
you can try a cone 10 porcelain and test it for absorption.
I hope that helps, if you can get Laguna clays.
John Hesselberth on tue 3 nov 09
On Nov 3, 2009, at 4:45 PM, Bob Johnson wrote:
> Can anyone tell me a good way to find out how vitrified the clay is?
> Absorbency? Ringing? Etc.?
Hi Bob,
Here is the way we recommend doing it in MC6Gs.
"Take an unglazed, but glaze fired test tile 1 or 2 inches wide by 3 =3D20
to 5 inches long x 0.5 inch thick. The size is not critical although =3D20
making it too thin can increase the error because of relatively more =3D20
surface area for water evaporation. On the other hand, if it is too =3D20
thick water may not penetrate all the way into the test sample. =3D20
Immediately on opening the kiln, carefully weigh it and record the =3D20
weight. Do not delay doing this or the result will be in error because =3D2=
0=3D
of pickup of atmospheric moisture. Weigh the sample while it is still =3D20=
=3D
warm. Submerge the tile in a pan of water and gently boil it for at =3D20
least two hours. Let the test sample cool to room temperature while it =3D2=
0=3D
is still submerged. When the test tile is cool, quickly remove it from =3D2=
0=3D
the pan, dry it carefully and promptly weigh it again. The fractional =3D20=
=3D
moisture absorption is calculated by [boiled weight-original weight] / =3D2=
0=3D
[original weight]. To convert to percentage, multiply by 100. If you =3D20
want a more rigorous and accurate determination of water absorption =3D20
see ASTM C373-88=3D97the procedure used by the whiteware industry which =
=3D20=3D
has been carefully validated."
Regards,
John
Ron Roy on fri 6 nov 09
Hi Sumi,
The standard test for absorbency recommended by Rhodes in Clay and Glazes
for the Potter is the same as yours but the boiling time is 2 hours - just
so no-one will think the results will be the same between the two different
boiling times.
RR
On Wed, Nov 4, 2009 at 12:44 AM, Sumi von Dassow wrote:
> Bob
>
> The absorbency test is to take a fired piece warm from the kiln and
> weigh it accurately on a gram scale;
> then immerse it in water, bring it to a boil, boil 5 minutes; let it
> cool down in the water; dry it off with a lint-free
> cloth, and weigh it again. Subtract the dry weight from the wet weight,
> divide the difference by the dry weight,
> and multiply by 100. That is your absorbency percentage. Vitrified clay
> has an absorbency of no more than
> about 3%.
>
> Sumi
>
> Thanks, Sumi (and others who made similar suggestions). I did try the
>> Laguna
>> ^5 B mix, but didn't like the gray I got in reduction; haven't tried the
>> ^10
>> version.
>>
>> Currently I'm working with some Georgie's ^10 Deschutes White for a Stev=
en
>> Hill workshop coming up next week--but I'll also try it in my kiln at ^6
>> in
>> reduction. If it works well, I'll let you know.
>>
>> Can anyone tell me a good way to find out how vitrified the clay is?
>> Absorbency? Ringing? Etc.?
>>
>> Bob
>>
>>
>>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
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