ernstm@musc.edu on mon 25 jan 99
I have this nice satin matt glaze called Patti's White which looks great at a
cone 7 but consistently underfires at anything below a 7. The glaze was
supposed to be a cone5-6 glaze. We used it in the classroom studio and also
in my home studio and it always looks underfired at cont 6. I tried adding
10% GB for a quick fix with inconsistent results. Would some of you glaze
gurus out there please look at this glaze formula and see what I could do to
lower the firing temperature on this glaze. I really like it. Thanks a lot. I
learn so much from your archives! Patti's White Flint 15 Ball clay 15 Soda
feldspar 20 Dolomite 20 Gerstley borate 12 Wollastonite 10 Zircopax 8
Any advise you've got would be appreciated. Thanks again, Mary
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David Hewitt on wed 27 jan 99
For a satin cone 6 glaze I would think that this is short on silica in
particular and also alumina. This can be corrected by adding china clay
and silica. The following recipe is what I would suggest. This using the
existing recipe and adding 10 parts flint and 30 parts EPK, so it would
read as follows:-
Flint 25
Ball Clay 15
Soda Feldspar 20
Dolomite 20
Gerstley borate 12
Wollastonite 10
Zircopax 8
EPK 30
---
140
K2O/Na2O .12 Al2O3 .47 SiO2 2.42
CaO .58 B2O3 .12 TiO2 .01
MgO .30 Fe2O3 .01 ZrO2 .11
This looks OK on limit formula for durability and reduces the
coefficient of expansion from 4.75 to 3.66 x10-6/oC Linear English &
Turner. One would not expect it to give rise to crazing.
David
In message , ernstm@musc.edu writes
>----------------------------Original message----------------------------
>I have this nice satin matt glaze called Patti's White which looks great at a
>cone 7 but consistently underfires at anything below a 7. The glaze was
>supposed to be a cone5-6 glaze. We used it in the classroom studio and also
>in my home studio and it always looks underfired at cont 6. I tried adding
>10% GB for a quick fix with inconsistent results. Would some of you glaze
>gurus out there please look at this glaze formula and see what I could do to
>lower the firing temperature on this glaze. I really like it. Thanks a lot. I
>learn so much from your archives! Patti's White Flint 15 Ball clay 15 Soda
>feldspar 20 Dolomite 20 Gerstley borate 12 Wollastonite 10 Zircopax 8
>Any advise you've got would be appreciated. Thanks again, Mary
>
>-----------== Posted via Deja News, The Discussion Network ==----------
>http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Ron Roy on fri 29 jan 99
Hi Mary,
The glaze Patti's white is short of silica - I have reformulated it with
enough silica, kept the expansion about the same and I am reasonably sure
it will melt well at cone 6 - if not send it back and I will fix it. I have
added a Frit (Ferro # 3134) to make it a more stable glaze in the bucket.
If you don't want to use it (or another Frit) I can reformulate with all
GB.
Ron's reformulation of Patti's white to make more durable.
-----------------
F4 SPAR............. 37.00
DOLOMITE............ 5.00
F3134............... 9.00
Gers Borate 9/97.... 9.00
WOLAST.............. 12.00
OM-4................ 15.00
SILICA.............. 13.00
ZIRCOPAX............ 7.00
----------
107.00
FORMULA & ANALYSIS
------------------
*CaO........ .50 10.90%
MnO2....... .00 .00%
*MgO........ .11 1.67%
*K2O........ .05 1.97%
*Na2O....... .17 3.96%
Fe2O3...... .00 .25%
TIO2....... .01 .18%
*B2O3....... .17 4.62%
AL2O3...... .30 11.86%
SiO2....... 2.59 60.01%
ZrO2....... .10 4.58%
RATIO 8.60 (was 9.12)
EXPAN 458.16 (was 465.64)
WEIGHT 258.55
>----------------------------Original message----------------------------
>I have this nice satin matt glaze called Patti's White which looks great at a
>cone 7 but consistently underfires at anything below a 7. The glaze was
>supposed to be a cone5-6 glaze. We used it in the classroom studio and also
>in my home studio and it always looks underfired at cont 6. I tried adding
>10% GB for a quick fix with inconsistent results. Would some of you glaze
>gurus out there please look at this glaze formula and see what I could do to
>lower the firing temperature on this glaze. I really like it. Thanks a lot. I
>learn so much from your archives! Patti's White Flint 15 Ball clay 15 Soda
>feldspar 20 Dolomite 20 Gerstley borate 12 Wollastonite 10 Zircopax 8
>Any advise you've got would be appreciated. Thanks again, Mary
>
>-----------== Posted via Deja News, The Discussion Network ==----------
>http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Burt Cohen on sat 30 jan 99
>
> -----------== Posted via Deja News, The Discussion Network ==----------
> http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Hi Mary-
I wouldn't line up in the Glaze guru line but if it was me I would take
your
20% of feldspar and replace half of it with Nepheline Syenite. It
usually lowers the fusion point without affecting the glaze. If you find
that doesn't do it completely sub out all of the feldspar with Neph
Syn-Cheers- Burt Cohen
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