Wanda Holmes on mon 1 apr 02
I forgot to give the unity value for B2O3 in the revised glaze. It is .08.
Wanda
-----Original Message-----
From: Wanda Holmes [mailto:wholmes@fortetechnology.com]
Sent: Monday, April 01, 2002 7:06 PM
To: Clayart
Subject: Glaze gurus, I could use your help
I tested Richard Behren's Satin Matt Cone 6 glaze and fell in love with the
waxy semi-matte surface. However, it leached badly in a 3-day vinegar test.
So, I set about to make it more durable. Despite my efforts, the "improved"
glaze still leaches almost as badly. Any insight any of you can offer would
be most appreciated.
The original recipe was:
Feldspar (I used Custer) 34.9
Whiting 12.62
Zinc oxide 25.8
EPK 4.10
Silica 22.6
.5 Cobalt carbonate added
The chemical formula is:
Na2O .03
K2O .08
MgO .00
CaO .25
ZnO .64
Al2O3 .15
SiO2 1.6
P2O5 .00
TiO2 .00
Fe2O3 .00
Al:Si 1:10.92
My improved recipe is:
Custer feldspar 25.8
Whiting 5.2
Zinc Oxide 18.6
EPK 9.3
Silica 26.7
Ferro Frit 3124
Cobalt carbonate .5
With a chemical formula of:
Na2O .07
K2O .08
MgO .00
CaO .24
ZnO .61
Al2O3 .25
SiO2 2.52
P2O5 .00
TiO2 .00
Fe2O3 .00
Al:Si 1:10.28
My strategy was to get it within the limits set out by Ron & John in
"Mastering Cone 6 Glazes", boost the alumina and silica up into the durable
range, keep the Al:Si ratio near the original values, & keep the fluxes near
their original values.
The surface quality of the new glaze is very like the original. The color
response is a bit less intense. Once again, it is a thing of beauty, but
not durable. Should I just keep boosting up the Al & Si until I find a
durable result or ruin the surface quality, whichever comes first?
Wanda
John Hesselberth on mon 1 apr 02
Hi Wanda,
This glaze has some unusual characteristics and is outside the range of what
I have tested so I am speculating to some degree. You say it is a waxy
semi-matte, yet it has a silica/alumina ratio of over 10. This would
clearly be in the glossy range so I speculate that you are not getting it
melted (rule 3). Of course it also violates Rules 1 and 2 as you noted.
Notice that it has very little K/Na, some calcium and lots of zinc. Yes
zinc is a good flux at cone 6, but not as good as K/Na.
When you then raised the Si and Al levels to meet minimum rule 1 and 2 goals
you made it even more difficult to melt. The little bit of boron you added
was probably not enough to get the job done--so you are still having a
problem with rule 3. If you took this glaze up to cone 8 - 10 it might do
better--that is the easiest way to see if it is a melting problem. Of
course the glaze will probably be glossy then.
So bottom line--my guess is that this is a good example of an unmelted
matte--and a great new example for me to add to my bag of
lemon-juice-test-tiles. Who else will hazard a guess?
Regards,
John
on 4/1/02 8:11 PM, Wanda Holmes at wholmes@FORTETECHNOLOGY.COM wrote:
> I forgot to give the unity value for B2O3 in the revised glaze. It is .08.
> Wanda
>
> -----Original Message-----
> From: Wanda Holmes [mailto:wholmes@fortetechnology.com]
> Sent: Monday, April 01, 2002 7:06 PM
> To: Clayart
> Subject: Glaze gurus, I could use your help
>
>
> I tested Richard Behren's Satin Matt Cone 6 glaze and fell in love with the
> waxy semi-matte surface. However, it leached badly in a 3-day vinegar test.
> So, I set about to make it more durable. Despite my efforts, the "improved"
> glaze still leaches almost as badly. Any insight any of you can offer would
> be most appreciated.
>
> The original recipe was:
> Feldspar (I used Custer) 34.9
> Whiting 12.62
> Zinc oxide 25.8
> EPK 4.10
> Silica 22.6
>
> .5 Cobalt carbonate added
>
> The chemical formula is:
> Na2O .03
> K2O .08
> MgO .00
> CaO .25
> ZnO .64
>
> Al2O3 .15
>
> SiO2 1.6
> P2O5 .00
> TiO2 .00
> Fe2O3 .00
>
> Al:Si 1:10.92
>
> My improved recipe is:
> Custer feldspar 25.8
> Whiting 5.2
> Zinc Oxide 18.6
> EPK 9.3
> Silica 26.7
> Ferro Frit 3124
> Cobalt carbonate .5
>
> With a chemical formula of:
> Na2O .07
> K2O .08
> MgO .00
> CaO .24
> ZnO .61
>
> Al2O3 .25
>
> SiO2 2.52
> P2O5 .00
> TiO2 .00
> Fe2O3 .00
>
> Al:Si 1:10.28
>
> My strategy was to get it within the limits set out by Ron & John in
> "Mastering Cone 6 Glazes", boost the alumina and silica up into the durable
> range, keep the Al:Si ratio near the original values, & keep the fluxes near
> their original values.
>
> The surface quality of the new glaze is very like the original. The color
> response is a bit less intense. Once again, it is a thing of beauty, but
> not durable. Should I just keep boosting up the Al & Si until I find a
> durable result or ruin the surface quality, whichever comes first?
>
> Wanda
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