Jacquelyn Lumsden on tue 18 feb 97
Does anyone have a recipe for a Cone 10 clear glaze that will not craze on
porcelaine in reduction. It seems to be a difficult thing to find. We have
glazes that work on stoneware, but not on porcelaine at cone 10 in
reduction.
Thanks for your help.
Jackie Lumsden
Waterloo, Ont.
Craig Martell on wed 19 feb 97
At 10:19 AM 2/18/97 EST, you wrote:
>----------------------------Original message----------------------------
> Does anyone have a recipe for a Cone 10 clear glaze that will not craze on
>porcelaine in reduction. It seems to be a difficult thing to find. We have
>glazes that work on stoneware, but not on porcelaine at cone 10 in
>reduction.
Hi: This glaze does not craze on any of the porcelain bodies that I have
used at cone 10R. However, I can't give you any absolute guarantees that it
will work as well for you. The history of this glaze is very short, I
formulated it in about 1980 for the same reasons that you are expressing, I
needed something that didn't craze and was very bright and clear. This
glaze has been working very well for me for the last 17 yrs with a few minor
adjustments from time to time. It will work in oxidation too. Craig
Martell-Oregon
Clear (cone 10 R or Ox.)
Dolomite 4.7% by weight
Whiting 15.9
g-200 feldspar 30.2
6-t kaolin 18.9
amorphous silica 30.3
add: Macaloid 1.5
Matthew Patton on thu 20 feb 97
----------
From: Ceramic Arts Discussion List on behalf of Jacquelyn Lumsden
Sent: Tuesday, February 18, 1997 7:19 AM
To: Multiple recipients of list CLAYART
Subject: Cone 10 Reduction Clear for Porcelaine
----------------------------Original message----------------------------
Does anyone have a recipe for a Cone 10 clear glaze that will not craze on
porcelaine in reduction. It seems to be a difficult thing to find. We have
glazes that work on stoneware, but not on porcelaine at cone 10 in
reduction.
Thanks for your help.
Jackie Lumsden
Waterloo, Ont.
Here is a glaze that I formulated to be particularly craze
resistant. Remember however that crazing is caused
(and allieviated) by many many differing phenomenon.
C10 CLEAR
SILICA 35
FELDSPAR 20
KAOLUIN 15
WHITING 15
GERSTLY BORATE 10
Good Luck! Matthew Patton mjpat@msn.com
Sam Cuttell on thu 20 feb 97
>formulated it in about 1980 for the same reasons that you are expressing, I
>needed something that didn't craze and was very bright and clear. This
>glaze has been working very well for me for the last 17 yrs with a few minor
>adjustments from time to time. It will work in oxidation too. Craig
>Martell-Oregon
>
>Clear (cone 10 R or Ox.)
>
>Dolomite 4.7% by weight
>Whiting 15.9
>g-200 feldspar 30.2
>6-t kaolin 18.9
>amorphous silica 30.3
>
>add: Macaloid 1.5
>
>
Dumb question time (yet again!!)
Can EPK be substituted for 6-t kaolin?
and
where do I buy amorphous silica?
Many thanks in advance
sam - alias the cat lady
Melbourne, Ontario, CANADA
http://www.geocities.com/paris/3110
Look for me at NCECA - I should be easy to spot. I wear long,
colourful skirts....
and, oh yeah; I have purple hair.
Crystal Larson on thu 20 feb 97
Hi there,
I was asking my instructors what could cause your crazing / crawling problem
and they think that your glaze or clay body may have to much magnesium in it
which causes a different shrinkage rate than that of the glaze, hense the
problem. It could also cause shivering, where the clay body shrinks more
than the glaze and will flake off. You might want to try modifying your
glaze recipe or change the type of porcelaine that your are using and see if
that is the problem.
Anyway, the clear glaze that we use at the college I attend is called Clear
Colemanite and I have used it on Porcelaine in reduction on top of glaze
inlays with excellent results as long as you put on a single coat. Double
coats tend to get a whitish look if the firing does not go to a true cone 10.
We fire in a gas kiln and I have never seen it crawl or craze on any of the
student work, my own included, that I have helped unload so I hope that this
will help you.
Please let me know if you have a problem with it as I am extremely interested
in how other peoples' kilns fire and what the results are since I don't have
my own kiln and use the school's kilns. I am giving the glaze recipe as it
is written for students to make up in the school batch:
Clear Colemanite: Cone 10 glaze
lbs ozs
Custer Feldspar 11 -
Ball clay 8 -
Whiting 8 -
Silica 15 -
Colemanite 4 -
Water - approximately 10 quarts
Good Luck
Crystal Larson
woosblue@aol.com
Debby Grant on fri 21 feb 97
Hi Jackie,
here is a ^ 9-10 clear glaze that works for me in both oxidation and
reduction.
Gerstley Borate - 21
Wollastonite - 8
Neph Sy - 30
EPK - 10
Flint - 31
Be careful not to use too thick as it could then turn milky.
Hope this helps. Good luck, Debby Grant
Craig Martell on fri 21 feb 97
At 07:12 AM 2/20/97 EST, you wrote:
>----------------------------Original message----------------------------
>Hi there,
>I was asking my instructors what could cause your crazing / crawling problem
>and they think that your glaze or clay body may have to much magnesium in it
>which causes a different shrinkage rate than that of the glaze, hense the
>problem. It could also cause shivering, where the clay body shrinks more
>than the glaze and will flake off. You might want to try modifying your
>glaze recipe or change the type of porcelaine that your are using and see if
>that is the problem.
Hi: Your insructors are assuming quite a lot, without even seeing the glaze
or clay formula. What their advice here amounts to is a total "shot in the
dark". The changes they recommend seem terribly radical if you take into
account that they have no knowledge of the materials being used.
If it were me, I would ignore this advice. They are suggesting that one
material, magnesium, is causing problems at both ends of the expansion
spectrum. Crazing and shivering are totally opposite and the advice here
suggests that one material is causing both. It just can't happen that way.
Regards, Craig in Oregon
Craig Martell on fri 21 feb 97
Sam the Cat lady wrote:
>Dumb question time (yet again!!)
>
>Can EPK be substituted for 6-t kaolin?
>
>and
>
>where do I buy amorphous silica?
>
>Many thanks in advance
Hi Sam: Sure, you can sub epk for 6-t and I don't think it will change the
glaze too much. 6-t is a bit more refractory.
Amorphous silica that I use is 325 mesh non-crystalline silica. Most
suppliers have it. If you have trouble getting amorphous, try what you have
on hand. Craig
Tony Hansen on fri 21 feb 97
Crystal:
It should not be necessary to use Colemanite in a cone 10 glaze. It
produces a glass that is not as hard and durable. Silica and Alumina
have very low expansion rates and cone 10 glazes have high amounts of
silica and alumina. There is a wide selection of fluxing materials
that will melt easily at cone 10 and form a very good interface layer
with the clay body. Thus it is the easiest temperature
range at which to fit a glaze. A typical cone 10 clear glaze should
have at least 20-25% kaolin and 30% flint/silica.
> Clear Colemanite: Cone 10 glaze
> lbs ozs
> Custer Feldspar 11 -
> Ball clay 8 -
> Whiting 8 -
> Silica 15 -
> Colemanite 4 ---
=================================================================
Tony Hansen, IMC - Get INSIGHT 5 beta or The Magic of Fire II at
http://digitalfire.com or http://www.ceramicsoftware.com
Tony Hansen on sun 23 feb 97
> Sure, you can sub epk for 6-t and I don't think it will change the
> glaze too much. 6-t is a bit more refractory.
Be careful if there is a lot of kaolin. 6t is the most plastic kaolin
you can buy, up to 7% dry shrinkage. EPK drastically less plastic.
High kaolin glazes will thus shrink more and possibly crack off. 6t
will suspend better but not gel as well. EPK is a very very good glaze
kaolin, don't sub if you don't have to. Also, 6t is hugely variable
in maturity and plasticity for the past two years.
--
=================================================================
Tony Hansen, IMC - Get INSIGHT 5 beta or The Magic of Fire II at
http://digitalfire.com or http://www.ceramicsoftware.com
Craig Martell on mon 24 feb 97
At 10:27 AM 2/23/97 EST, Tony Hansen wrote:
>Be careful if there is a lot of kaolin. 6t is the most plastic kaolin
>you can buy, up to 7% dry shrinkage. EPK drastically less plastic.
>High kaolin glazes will thus shrink more and possibly crack off. 6t
>will suspend better but not gel as well. EPK is a very very good glaze
>kaolin, don't sub if you don't have to. Also, 6t is hugely variable
>in maturity and plasticity for the past two years.
Thanks for pointing this out Tony. I've been using the same batch of 6-t
kaolin for the past 5 years. I bought a lot! I use up to 20% raw,
uncalcined, 6-t in my glazes and I haven't had any problems yet. I use EPK
in some glazes as well and I think I should do a substitution in the glazes
with 6-t and see how it goes.
Thanks again, Craig Martell-Oregon
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