Gloria Davidson on thu 24 jul 97
Hi All,
I have a problem with the following glaze that I hope some of the
glaze chemistry Guru's out there might be able to help me with. I have used
this glaze for years now with good success but it requires cone 10 flat and
11 tipping to mature. I would like to lower the temp. to a 9 flat and cone
10 tipping but don't really know where to begin. I fire a 35 cubic ft.
Minnesota Flat Top with natural gas. If anyone can get me started, I would
be grateful.
Also, I have been trying to paint with stains over this glaze. I
use them mixed with water and gerstly borate but can't get a smooth flow
going. I was wondering how mixing the stains right in with some of the
Buttermilk would work. Does anyone have suggestions???
Many thanks for your time. I love this group and have learned so
much from reading your shares.
Gloria
Buttermilk
Gherstly Borate 10.5% Kaolin 6.8%
Dolomite 6.8% Talc 13.5%
Whiteing 9.0% Flint 24.1%
Potash Feldspar 29.3%
Opax 8.0%
My Turn Pottery
Tony Hansen on sat 26 jul 97
> I have used
> this glaze for years now with good success but it requires cone 10 flat and
> 11 tipping to mature. I would like to lower the temp. to a 9 flat and cone
> 10 tipping but don't really know where to begin.
> Gherstly Borate 10.5%, Kaolin 6.8%, Dolomite 6.8%, Talc 13.5%
> Whiteing 9.0%, Flint 24.1%, Potash Feldspar 29.3%, Opax 8.0%
Just add feldspar in 5% amounts till its looks right.
However it is possible the surface character relies on
some sort of magnesia mechanism and there is plenty in this glaze. Or
with
the low Al2O3 it might be a crystalization effect. This mechanism may or
may
not like to move downward, depending on the degree of temperature
dependence.
It is possible that adding feldspar might upset the oxide balance that
produces
the surface effect.
I didn't have time to convert this glaze to a formula but that low
kaolin
and feldspar sure looks suspicious. Without adequate alumina to
stabilize
the melt I'd be careful about leaching.
--
T o n y H a n s e n, I M C thansen@digitalfire.com
=========================================================
INSIGHT5/Magic of Fire II demos at http://digitalfire.com
David Hewitt on sat 26 jul 97
At the recent Aberystwyth Potters Festival I listened to David Frith
recounting how some years back when fuel costs were going up very
significantly, he decided to reformulate his glazes to work at lower
cones (down from 10 to 8). While this was possible, he was not satisfied
as there was always some difference in the final results. He then tried
ball milling his glazes for some hours (I think he mentioned 6 hours or
may be longer) and this produced the desired result and the same final
effect at cone 8 which had previously been obtained at cone 10.
I have no direct experience of this technique, but perhaps it will be of
interest to you. Has any other Clayart reader experience of this?
In message , Gloria Davidson writes
>----------------------------Original message----------------------------
>Hi All,
> I have a problem with the following glaze that I hope some of the
>glaze chemistry Guru's out there might be able to help me with. I have used
>this glaze for years now with good success but it requires cone 10 flat and
>11 tipping to mature. I would like to lower the temp. to a 9 flat and cone
>10 tipping but don't really know where to begin. I fire a 35 cubic ft.
>Minnesota Flat Top with natural gas. If anyone can get me started, I would
>be grateful.
> Also, I have been trying to paint with stains over this glaze. I
>use them mixed with water and gerstly borate but can't get a smooth flow
>going. I was wondering how mixing the stains right in with some of the
>Buttermilk would work. Does anyone have suggestions???
> Many thanks for your time. I love this group and have learned so
>much from reading your shares.
>Gloria
>
>Buttermilk
>
>Gherstly Borate 10.5% Kaolin 6.8%
>Dolomite 6.8% Talc 13.5%
>Whiteing 9.0% Flint 24.1%
>Potash Feldspar 29.3%
>
>Opax 8.0%
>
>My Turn Pottery
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
URL http://www.ceramicsoftware.com/education/people/hewitt.htm
Ric Swenson on sun 27 jul 97
-------reply------
yes, making the particle size smaller makes materials (generally) melt at a
lower temperature (I'm quite certain there are exceptions, but that is a
good way to lower the PCE of a glaze without re-formulating. One or two
cones lower is all I have heard about trying.
Another method that F.Carlton Ball was fond of was replacing part or all of
the feldspar in a glaze with Nepheline Syenite to drop a Pyrometric Cone
Equivalent or two (maybe)
There may be other materials that available to you that will produce good
results when you experiment.
When Bennington Potters dropped from cone 9 to cone 6 after the energy
crisis in the 70s, and went to a fast fire Keith tunnel kiln (about 5 hours
cold/cold) the base glaze changed to a Fusion Ceramics frit F-18. BTW,
in 1983, after meeting the manager of KYANITE Corp. at an American Ceramics
Society Convention, a suggested trial clay body with addition of 10 % (200
mesh) raw KYANITE improved survival rates of large pieces through the
tunnel dramatically.
Ric
>----------------------------Original message----------------------------
>At the recent Aberystwyth Potters Festival I listened to David Frith
>recounting how some years back when fuel costs were going up very
>significantly, he decided to reformulate his glazes to work at lower
>cones (down from 10 to 8). While this was possible, he was not satisfied
>as there was always some difference in the final results. He then tried
>ball milling his glazes for some hours (I think he mentioned 6 hours or
>may be longer) and this produced the desired result and the same final
>effect at cone 8 which had previously been obtained at cone 10.
>
>I have no direct experience of this technique, but perhaps it will be of
>interest to you. Has any other Clayart reader experience of this?
>
>In message , Gloria Davidson writes
>>----------------------------Original message----------------------------
>>Hi All,
>> I have a problem with the following glaze that I hope some of the
>>glaze chemistry Guru's out there might be able to help me with. I have used
>>this glaze for years now with good success but it requires cone 10 flat and
>>11 tipping to mature. I would like to lower the temp. to a 9 flat and cone
>>10 tipping but don't really know where to begin. I fire a 35 cubic ft.
>>Minnesota Flat Top with natural gas. If anyone can get me started, I would
>>be grateful.
>> Also, I have been trying to paint with stains over this glaze. I
>>use them mixed with water and gerstly borate but can't get a smooth flow
>>going. I was wondering how mixing the stains right in with some of the
>>Buttermilk would work. Does anyone have suggestions???
>> Many thanks for your time. I love this group and have learned so
>>much from reading your shares.
>>Gloria
>>
>>Buttermilk
>>
>>Gherstly Borate 10.5% Kaolin 6.8%
>>Dolomite 6.8% Talc 13.5%
>>Whiteing 9.0% Flint 24.1%
>>Potash Feldspar 29.3%
>>
>>Opax 8.0%
>>
>>My Turn Pottery
>>
>
>--
>David Hewitt
>David Hewitt Pottery ,
>7 Fairfield Road, Caerleon, Newport,
>South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
>URL http://www.ceramicsoftware.com/education/people/hewitt.htm
Ric Swenson, Bennington College, Route 67-A, Bennington, Vermont,
05201-6001 USA. telephone 802 442 - 5401 vox X 262 fax X 237
direct fax line
802 442 - 6164
rswenson@bennington.edu
Debby Grant on mon 28 jul 97
Hello Gloria,
I have been using this same glaze for years. Got it out of CM. In fact
I have recently posted it to Clay Art. However I do not fire it quite as
high as you do - only to a slight ^10 bend. I have used it in both oxidation
and reduction but prefer it in oxidation. It is quite opaque so you will
not get very much color differentiation by just painting stains over it.
An iron slip works quite well but I always do my brush work on the
bisqued pot under the glaze. You might try some of the coloring oxides
in the glaze itself. I have already posted them.
Good luck, Debby Grant in NH
Ron Roy on mon 28 jul 97
>----------------------------Original message----------------------------
>Hi All,
> I have a problem with the following glaze that I hope some of the
>glaze chemistry Guru's out there might be able to help me with. I have used
>this glaze for years now with good success but it requires cone 10 flat and
>11 tipping to mature. I would like to lower the temp. to a 9 flat and cone
>10 tipping but don't really know where to begin. I fire a 35 cubic ft.
>Minnesota Flat Top with natural gas. If anyone can get me started, I would
>be grateful.
> Also, I have been trying to paint with stains over this glaze. I
>use them mixed with water and gerstly borate but can't get a smooth flow
>going. I was wondering how mixing the stains right in with some of the
>Buttermilk would work. Does anyone have suggestions???
> Many thanks for your time. I love this group and have learned so
>much from reading your shares.
>Gloria
>
>Buttermilk
>
>Gherstly Borate 10.5% Kaolin 6.8%
>Dolomite 6.8% Talc 13.5%
>Whiteing 9.0% Flint 24.1%
>Potash Feldspar 29.3%
>
>Opax 8.0%
Hi Gloria,
I may have lowered the temperature too much - so - mix this one (500 grams)
and test it in a cool part of your kiln (with large cones beside it. Then
mix equal parts (by volume) with your original. This will give you the
recipe between the two. If it is better than either the new one I am
sending add each ingrediant together (fome my new one and your old one) to
get the recipe for the middle one. Gerstley borate 10.5 + 13.0 = 23.5
divided by 2 =11.75 for instance.
Gerstley Borate - 13.0
Dolomite - 6.0
Whiting - 9.0
G200 spar - 29.0 (or Custer)
EPK - 6.0 (or whatever kaolin you are using)
Talc - 16.0
Silica - 21.0
Opax - 8
Total 108.0
Ratio - 11.52 (yours is 11.49)
Expansion - 443.23 (yours is 433.52)
By the way both glazes are seriously short of Alumina and Silica and
oversupplied with Magnesium so don't consider this a durable glaze. There
is not a toxicity problem because there are no problematic oxides in the
glaze - just be careful what you mix with and put under or over this glaze
in areas that will come in contact with food.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
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