Tracy Wilson on sun 29 mar 98
OK ...OK... Friends from Clayart...
Sometimes I can help and sometimes I need help
This time I need help.
I have a great kiln. 40 cu ft downdraft propane fired that is usually pretty
even in temp from top to bottom. Well maybe a cone off. ^9 at the top and
^10 at the bottom. All my glazes look good in that range but one. It's
milky at ^9 and beautiful at ^10. If I fire to ^10 at the top I'm almost
burying ^11 at the bottom which is hotter than I (or the bottom pots) like.
My question is this...
How can I lower the maturation temp of this glaze?
^10 glossy transparent gray
flint 36
potash spar (g-200) 23
EPK 18
Whiting 14
Talc 9
________
100
Can I reduce the EPK by 2% and raise the talc by 2% (as in Chappell's book)
Could it be that simple? I unfortunately don't have the benefit of INSIGHT
and my glaze calculation class was over 20 years ago (read rusty) Any
suggestions?
Thanks SO much in advance...
------------------------------------
Tracy Wilson
Saltbox Pottery
4 Shaw Rd.
Woolwich, ME 04579
phone: 207-443-5586
fax: 207-442-8922
email: saltbox@ime.net
web: http://www.ime.net/~dwilson/
-------------------------------------
Cat81257 on mon 30 mar 98
dear Tracy :
you asked something I can answer..... I lower the maturing temps on my glaze
by the interchange of ball clay for the epk. you can try 50/50 25/75 etc . I
use a ^10 mamo in gas reduction , 25% epk and 75% ball gave me a nice satin
sheen vs all epk giving a matt .. all ball made a great liner glaze . Test it
in varying combo's . its direct sub for epk. e mail me at Cat81257@aol.com
if you have any ????
Craig Martell on mon 30 mar 98
At 01:36 PM 3/29/98 EST, Tracy Wilson wrote:
>----------------------------Original message----------------------------
>How can I lower the maturation temp of this glaze?
>Can I reduce the EPK by 2% and raise the talc by 2% (as in Chappell's book)
>Could it be that simple?
Tracy:
Here's the current formula for your glaze:
Untitled Recipe 1
G200 FELDSPAR 23.00 CaO 0.57*
WHITING 14.00 MgO 0.28*
TALC 9.00 K2O 0.09*
EPK KAOLIN 18.00 Na2O 0.05*
SILICA 36.00 Fe2O3 0.00
======== TiO2 0.00
100.00 Al2O3 0.43
SiO2 4.27
Cost/kg 0.23
Si:Al 9.84
SiB:Al 9.84
Expan 5.90
It's a bit low in KNaO, so let's try bringing it up to the lower limit of
2.0 moles and see what happens. This will be done by raising the g-200,
which will also bring up the alumina and silica, so we can adjust the silica
and kaolin to keep that part of the glaze stable. Mix up a test and fire.
You should see a better melt and a more transparent glaze. Lets hope so
anyway. The adjustment is below. Oh, before I forget, the calculated
expansion of the original glaze is a bit low and if it comes up a bit in the
adjustment, it shouldn't hurt glaze fit.
Adjusted ^10 Trans. Grey
G200 FELDSPAR 31.42 CaO 0.54*
WHITING 13.13 MgO 0.26*
TALC 8.44 K2O 0.13*
EPK KAOLIN 13.77 Na2O 0.07*
SILICA 33.24 Fe2O3 0.00
======== TiO2 0.00
100.00 Al2O3 0.43
SiO2 4.27
Cost/kg 0.27
Si:Al 9.87
SiB:Al 9.87
Expan 6.19
Well, try this and see what happens. You should see a better melt and the
glaze is withing limits for a good, balanced, functional glaze. The
expansion is still a bit low, but slightly improved.
later, Craig Martell-Oregon
David Hewitt on tue 31 mar 98
Tracey,
This glaze looks to me to be high in Silica at 4.26 Seger formula.
I would suggest doing a line blend on the flint, taking this down to 10
parts.
With flint at 15 parts the silica comes down to 2.89 and the Al2O3/SiO2
ratio down from 1:10.01 to 1:6.79
David
In message , Tracy Wilson writes
>----------------------------Original message----------------------------
>
>OK ...OK... Friends from Clayart...
>Sometimes I can help and sometimes I need help
>This time I need help.
>I have a great kiln. 40 cu ft downdraft propane fired that is usually pretty
>even in temp from top to bottom. Well maybe a cone off. ^9 at the top and
>^10 at the bottom. All my glazes look good in that range but one. It's
>milky at ^9 and beautiful at ^10. If I fire to ^10 at the top I'm almost
>burying ^11 at the bottom which is hotter than I (or the bottom pots) like.
>My question is this...
>How can I lower the maturation temp of this glaze?
>
>^10 glossy transparent gray
>
>flint 36
>potash spar (g-200) 23
>EPK 18
>Whiting 14
>Talc 9
> ________
> 100
>
>Can I reduce the EPK by 2% and raise the talc by 2% (as in Chappell's book)
>Could it be that simple? I unfortunately don't have the benefit of INSIGHT
>and my glaze calculation class was over 20 years ago (read rusty) Any
>suggestions?
>Thanks SO much in advance...
>
>------------------------------------
>Tracy Wilson
>Saltbox Pottery
>4 Shaw Rd.
>Woolwich, ME 04579
>phone: 207-443-5586
>fax: 207-442-8922
>email: saltbox@ime.net
>web: http://www.ime.net/~dwilson/
>-------------------------------------
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Vince Pitelka on tue 31 mar 98
At 09:10 AM 3/30/98 -0500, you wrote:
>----------------------------Original message----------------------------
> dear Tracy :
>you asked something I can answer..... I lower the maturing temps on my glaze
>by the interchange of ball clay for the epk. you can try 50/50 25/75 etc . I
>use a ^10 mamo in gas reduction , 25% epk and 75% ball gave me a nice satin
>sheen vs all epk giving a matt .. all ball made a great liner glaze . Test it
>in varying combo's . its direct sub for epk. e mail me at Cat81257@aol.com
>if you have any ????
Be careful with this. I could certainly work lots of the time, but remember
that it is the clay content which makes glazes stick to the surface of pots,
and we usually adjust the ratio of kaolin to ball clay to adjust application
problems, rather than for relative fluxing affect (although that is
certainly a consideration as well). For a glaze with fairly high clay
content, substitution of some or all of the kaolin with ball clay could
cause serious problems. Ball clay of course features high shrinkage in
drying, and excessive ball clay could cause your glaze to crack badly in
drying.
There is an exception to everything. Years ago, when I was experiencing
sudden problems with shivering on a favored satin clear glaze, I replaced
some of the kaolin with ball clay (slightly reducing the alumina content),
and the shivering dissappeared, with no increased problems in application.
As I said, just be careful, and test a small batch before modifying a big
bucket full.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
GURUSHAKTI on wed 1 apr 98
Dear Tracy:
You can lower it a couple of cones just by replacing the feldspar with a soda
spar. If you only want to lower it a bit, try doing a test replacing half the
Potash feldspar with a soda feldspar like Kona F-4 soda feldspar or Nephenline
Syenite.
Good luck!
June
Ron Roy on fri 3 apr 98
Hi Tracy,
I need to know what kind of clay you are using - the expansion of your
glaze is low and lowering the EPK and raising the talc won't do much to
address that problem. Other wise this should be a piece fo cake to fix.
rr
>OK ...OK... Friends from Clayart...
>Sometimes I can help and sometimes I need help
>This time I need help.
>I have a great kiln. 40 cu ft downdraft propane fired that is usually pretty
>even in temp from top to bottom. Well maybe a cone off. ^9 at the top and
>^10 at the bottom. All my glazes look good in that range but one. It's
>milky at ^9 and beautiful at ^10. If I fire to ^10 at the top I'm almost
>burying ^11 at the bottom which is hotter than I (or the bottom pots) like.
>My question is this...
>How can I lower the maturation temp of this glaze?
>
>^10 glossy transparent gray
>
>flint 36
>potash spar (g-200) 23
>EPK 18
>Whiting 14
>Talc 9
> ________
> 100
>
>Can I reduce the EPK by 2% and raise the talc by 2% (as in Chappell's book)
>Could it be that simple? I unfortunately don't have the benefit of INSIGHT
>and my glaze calculation class was over 20 years ago (read rusty) Any
>suggestions?
>Thanks SO much in advance...
>
>------------------------------------
>Tracy Wilson
>Saltbox Pottery
>4 Shaw Rd.
>Woolwich, ME 04579
>phone: 207-443-5586
>fax: 207-442-8922
>email: saltbox@ime.net
>web: http://www.ime.net/~dwilson/
>-------------------------------------
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
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