Gayle Bair on mon 30 oct 00
I got this glaze from Clayart over a year ago.
The color is lovely and slip shows through very nicely.
The problem is crazing on all the different stoneware
and porcelain clay bodies I have used.
I slow fire ^5 and have tried various soaks 20-60 minutes.
I admit that I have an inability to wait until the kiln is below
150 degrees so I start unloading then.
Also what GB substitute would you suggest?
Personally I like the crazing as I like the antique look.
However I don't want to use it on the interior of functional pots.
If there is a way to eliminate the crazing I would be most grateful.
Faux Celedon Cone 5-6
Kona F4 Soda feldspar 50
Wollastonite 20 (I use W-30)
China Clay 10 (I've been using Grolleg)
Silica 10 (I use 20% to reduce crazing on Bmix
5)
Gertsley Borate 10 (haven't tried any of the substitutes
yet)
Copper carbonate 0.5
Black Stain 0.2 (I use Mason 6650)
TIA
Gayle Bair- still crazed after all these years! And another thing
I am finding all this commercial dinnerware that appears crazed.
Do they seal it with a clear glaze or what???
Just curious and thinking about the recent thread on selling
work with crazing. So how can they sell it?
Marcia Selsor on tue 31 oct 00
Gayle,
I use a nice clear base that fits my porcelain with no crazing. I will
try your glaze and see what happens
Whiting 18.5
Neph Sy 25.8
EPK 18.8
Silica 31.1
Gerst. Borate 4.6
(for gas celedon I use 1.5 Spanish Iron, for electric faux celedon 1.5
copper carb. / red in reduction try 1 Tin oxide and .75 copper carb.)
I am working on glazes good in both systems but have different looks.
I'll let you know how it fits my porcelain. I am using the Bray
porcelain so I can't tell you what's in it. I switched from mixing my
own because the glazes fit better.
Marcia
Gayle Bair wrote:
>
> I got this glaze from Clayart over a year ago.
> The color is lovely and slip shows through very nicely.
> The problem is crazing on all the different stoneware
> and porcelain clay bodies I have used.
> I slow fire ^5 and have tried various soaks 20-60 minutes.
> I admit that I have an inability to wait until the kiln is below
> 150 degrees so I start unloading then.
> Also what GB substitute would you suggest?
>
> Personally I like the crazing as I like the antique look.
> However I don't want to use it on the interior of functional pots.
>
> If there is a way to eliminate the crazing I would be most grateful.
>
> Faux Celedon Cone 5-6
>
> Kona F4 Soda feldspar 50
> Wollastonite 20 (I use W-30)
> China Clay 10 (I've been using Grolleg)
> Silica 10 (I use 20% to reduce crazing on Bmix
> 5)
> Gertsley Borate 10 (haven't tried any of the substitutes
> yet)
>
> Copper carbonate 0.5
> Black Stain 0.2 (I use Mason 6650)
>
> TIA
> Gayle Bair- still crazed after all these years! And another thing
> I am finding all this commercial dinnerware that appears crazed.
> Do they seal it with a clear glaze or what???
> Just curious and thinking about the recent thread on selling
> work with crazing. So how can they sell it?
>
> ______________________________________________________________________________
> 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.
--
Marcia Selsor
selsor@imt.net
http://www.imt.net/~mjbmls
http://www.imt.net/~mjbmls/spain99.html
http://www.silverhawk.com/ex99/selsor/welcome.html
Craig Martell on wed 1 nov 00
Hello Gayle:
I looked at this glaze with Insight and Matrix. It's a very good, well
balanced cone 5-6 glaze. The alumina and silica are both in the cone 10
range actually. I don't know how badly the glaze is crazing but you need
to lower the sodium a bit. One thing to try is a direct sub of Cady Cal
100 for the Gerstley Borate. Boron has a low COE and may help the
crazing. The problem with GB is that is also contains sodium so if you
increase the GB for more boron to lower expansion you are actually
increasing the expansion due to the sodium content of GB. Cady Cal has
virtually no sodium so this may do the trick. If a direct sub doesn't work
you can add more Cady at 5% increments and hopefully move toward better
glaze fit.
regards, Craig Martell in Oregon
David Hewitt on thu 2 nov 00
Using my glaze calculator, the Glaze Workbook, The recipe you quote
comes out with a linear expansion coefficient of 5.62 x 10-6/oC using
English & Turner coefficients.
>From my experience I am not surprised that it crazes on porcelain. The
clear transparent glaze that I use on porcelain to avoid crazing has a
coefficient of 2.93.
Using your materials and the data that I have on them, you can adjust
the recipe to lower the coefficient to 3.06 as follows:-
Kona F4 3.6
Wollastonite 7.0
China clay 25.0
Silica 28.6
GB 35.8
----
100
I have not tested this so cannot say how it will perform, so it is up to
you if you want to test it.
The recipe that I use is:-
Wollastonite 82
China clay 175
Potash feldspar 39
Zinc oxide 13
Lithium Carbonate 12
Dolomite 39
Silica 256
BPS Low Exp Frit 384
----
1000
In message , Gayle Bair writes
>I got this glaze from Clayart over a year ago.
>The color is lovely and slip shows through very nicely.
>The problem is crazing on all the different stoneware
>and porcelain clay bodies I have used.
>I slow fire ^5 and have tried various soaks 20-60 minutes.
>I admit that I have an inability to wait until the kiln is below
>150 degrees so I start unloading then.
>Also what GB substitute would you suggest?
>
>Personally I like the crazing as I like the antique look.
>However I don't want to use it on the interior of functional pots.
>
>If there is a way to eliminate the crazing I would be most grateful.
>
>Faux Celedon Cone 5-6
>
>Kona F4 Soda feldspar 50
>Wollastonite 20 (I use W-30)
>China Clay 10 (I've been using Grolleg)
>Silica 10 (I use 20% to reduce crazing on Bmix
>5)
>Gertsley Borate 10 (haven't tried any of the substitutes
>yet)
>
>
>Copper carbonate 0.5
>Black Stain 0.2 (I use Mason 6650)
>
>TIA
>Gayle Bair- still crazed after all these years! And another thing
>I am finding all this commercial dinnerware that appears crazed.
>Do they seal it with a clear glaze or what???
>Just curious and thinking about the recent thread on selling
>work with crazing. So how can they sell it?
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
DONALD G. GOLDSOBEL on thu 2 nov 00
Craig, If I wanted to substitute Cadycal for Gerstly B what would I add to
get a non-soluble source of sodium..
TIA
Donald G.
At 10:14 PM 11/01/2000 -0800, you wrote:
>Hello Gayle:
>
>I looked at this glaze with Insight and Matrix. It's a very good, well
>balanced cone 5-6 glaze. The alumina and silica are both in the cone 10
>range actually. I don't know how badly the glaze is crazing but you need
>to lower the sodium a bit. One thing to try is a direct sub of Cady Cal
>100 for the Gerstley Borate. Boron has a low COE and may help the
>crazing. The problem with GB is that is also contains sodium so if you
>increase the GB for more boron to lower expansion you are actually
>increasing the expansion due to the sodium content of GB. Cady Cal has
>virtually no sodium so this may do the trick. If a direct sub doesn't work
>you can add more Cady at 5% increments and hopefully move toward better
>glaze fit.
>
>regards, Craig Martell in Oregon
>
>___________________________________________________________________________
___
>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.
>
Craig Martell on fri 3 nov 00
Donald asked:
>Craig, If I wanted to substitute Cadycal for Gerstly B what would I add to
>get a non-soluble source of sodium..
Hi:
I would use soda feldspar or nepheline syenite. There are several soda
spars available and you could look at the analyses to determine which one
would give you the most soda. I haven't done this yet but you could also
look at the composition of some of Fusion's frits. They make some unusual
ones that are more applicable to studio potters instead of industry. I
just used Fusion 493 in Shino biaxial test and it produced some very nice
glazes. It is mainly a sodium-lithium frit which is sort of a shino
blend. This is just an example but I think there are probably some good
possibilities for non soluble sodium additions with Fusion.
later, Craig Martell in Oregon
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