Lou Roess on sun 6 feb 05
Thanks to everyone who answered my first post about the following
recipe:
> BASE GLAZE Cone 6 OX
>
> 38 Custer Feldspar
> 22 Gerstley Borate
> 4 Strontium Carb
> 11 Whiting
> 25 Flint
> 2% Bentonite
Would anyone care to take it one step further and refigure for more
alumina which it seems to need, and/or a substitution for the GB?
I'd appreciate any help. I'm looking at glaze software but haven't
made the jump yet. Time to recheck the archives. I know there's lots
of information there.
Thanks,
Lou in Colorado
David Hewitt on tue 8 feb 05
Lou,
If I were you I wouldn't use Gerstley Borate as it is too variable and
has other disadvantage. I would use a frit in its place. In fact I would
suggest starting from a different recipe such as shown in Mike Bailey's
book 'Glazes Cone 6. Ones which are clear transparent base glazes like
T12 or BOT2 which does use a calcium borate frit and which one would not
expect to craze on a porcelain body.
T12
Potas feldspar 44.0
China clay 6.0
Bentonite 2.0
Lithium carbonate 4.0
Whiting 14.0
Zinc oxide 5.0
Flint or Quartz 24.0
0.18 K2O 0.32 Al2O3 2.81 SiO2
0.06 Na2O
0.16 Li2O
0.42 CaO
0.18 ZnO
COE 5.52 x 10-6/oC English & Turner
BOT2
Potash felspar 36.4
Calcium borate frit 14.7
China clay 5.0
Lithium carbonate 5.1
Talc 11.7
Zinc oxide 3.9
Quartz 23.2
0.04 K2O 0.26 Al2O3 2.88 SiO2
0.13 Na2O .0.30 B2)3
0.20 Li2O
0.26 CaO
0.23 MgO
0.14 ZnO
COE 3.62 x 10-6/oC English & Turner
These recipes and their analyses are, of course, using Mike's raw
materials. Yours might be slightly different. If you do know the
analysis of yeach of your materials and had a glaze program, then you
could tweek these recipes to suit. I would think, however, that it would
be sensible to just test using your materials and see how they perform.
David.
In message , Lou Roess writes
>Thanks to everyone who answered my first post about the following
>recipe:
>
>> BASE GLAZE Cone 6 OX
>>
>> 38 Custer Feldspar
>> 22 Gerstley Borate
>> 4 Strontium Carb
>> 11 Whiting
>> 25 Flint
>> 2% Bentonite
>
>Would anyone care to take it one step further and refigure for more
>alumina which it seems to need, and/or a substitution for the GB?
>I'd appreciate any help. I'm looking at glaze software but haven't
>made the jump yet. Time to recheck the archives. I know there's lots
>of information there.
>Thanks,
>Lou in Colorado
--
David Hewitt
Web:- http://www.dhpot.demon.co.uk
John Hesselberth on tue 8 feb 05
Hi Lou,
Ok, I'll give it a try. First let me explain my approach. I used my
9/97 analysis for Gerstley Borate--that is always a guess since GB is
so variable. I decided to try to raise alumina from .22 up to 0.3. When
replacing GB with a frit I have found it works best to also replace EPK
with a ball clay. I chose OM4 which is readily available in North
America. It is only a guess, but it would seem that some of the trace
ingredients in ball clay might be similar to those in GB--anyhow it
seems to work better if I do it that way. Lastly I did not try to
balance Na and K individually--only the total of the two. So here is
the recipe.
Base Glaze--GB free
Feldspar--Custer 18.9
Frit--Ferro 3134 28.0
Whiting 8.3
Strontium Carbonate 4.1
Talc 2.4
Ball Clay--OM#4 22.9
Silica 15.4
Total 100.0
You can add bentonite if you need it, but I really believe there is
enough clay in this recipe that it shouldn't be needed. I try not to
use things that don't add a benefit.
Give it a try and let us know the results. It may be slightly different
in aesthetics with the higher alumina level, but I'm betting not much.
Regards,
John
P.S. Deriving the above took about 5 minutes with the help of glaze
calculation software (GlazeMaster, of course)
On Sunday, February 6, 2005, at 08:09 PM, Lou Roess wrote:
> Thanks to everyone who answered my first post about the following
> recipe:
>
>> BASE GLAZE Cone 6 OX
>>
>> 38 Custer Feldspar
>> 22 Gerstley Borate
>> 4 Strontium Carb
>> 11 Whiting
>> 25 Flint
>> 2% Bentonite
>
> Would anyone care to take it one step further and refigure for more
> alumina which it seems to need, and/or a substitution for the GB?
> I'd appreciate any help. I'm looking at glaze software but haven't
> made the jump yet. Time to recheck the archives. I know there's lots
> of information there.
> Thanks,
> Lou in Colorado
>
> _______________________________________________________________________
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>
>
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
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