iglasgo on mon 9 apr 07
I'm having endless fun testing glazes, so I thought I'd post a couple
of them. I've also posted a couple photos at
http://outinmonument.blogspot.com/
I'm working on getting a perfect copper blue for some tiles I'm
making for my in-laws... Food safety per se isn't necessary, and the
crazing is not a problem, but the glaze needs to be durable enough to
stand up to my MIL's cleaning regimen. I tested my Cone 04 formula and
it's just not durable enough.
So I decided to try for a Cone 6 copper blue to match the low-fire
glaze. What did I get myself into... After what seems like a
million tests & recalculations I have arrived at this formula.
The color is absolutely perfect. Gorgeous, deep, exquisite. Just a
tiny bit of brown where it breaks on edges. The surface is a smooth,
tactile dry matte with a few sugary crystals. Crazed, but not too
crazed. It runs like crazy. But the color, oh, it is so delicious, and
it is durable enough that it is not harmed by 36 hours in vinegar.
Someone else might find this glaze to be perfect for their
use. The only problem for me is that I really want a glossy glaze
that doesn't break too much or run.
Here's the recipe & analysis:
My copper blue so far, ^6 ox.
Nepheline syenite 46
Strontium carbonate 19
Lithium carbonate 6
Whiting 3.5
Kentucky OM #4 2.5
Silica 19
Frit 3134 4
Add:
Copper carbonate 5
Cobalt carbonate 0.025
Na2O 0.23
K2O 0.06
CaO 0.14
Li2O 0.22
SrO 0.35
Al2O3 0.30
B2O3 0.04
SiO2 2.24
So obviously this glaze is really high in strontium which I guess is
what's making it matte. I have tried a version with more silica which
did make it more glossy but also turned the glaze to a typical green
color. Omitting the lithium made it less runny but also hurt the
color. So I don't know where to go from here in trying to make it do
what I want it to do. Would adding EPK stiffen it up without hurting
the color response? Any other ideas?
The other glaze I'm perfectly happy with the color and surface, but I
don't know if it would be considered stable or not. It was a very
unexpected result of a line blend of my cone 04 copper blue glaze and
a cone 8 high calcium glaze. It has a nice semi-gloss surface, though
it is heavily crazed.
It is a light blue-green where thin, and deep green where very thick.
Where it is medium thickness it appears like there's brown, almost
metallic copper colored crystals floating on the surface. The overall
effect is kind of like a mysterious, swampy bayou.
Here's the recipe & analysis:
Copper brown, ^6 ox.
G-200 feldspar 27
Nepheline syenite 16.5
Whiting 19
Strontium carbonate 3
Soda ash 7
EPK 5.5
Silica 17
Frit 3134 5
Add:
Copper carbonate 3
Na2O 0.29
K2O 0.10
MgO 0.00
CaO 0.55
SrO 0.05
Al2O3 0.28
B2O3 0.04
SiO2 2.16
My guess from the numbers is that it's not stable, but I don't really
know. Is it close? If I added EPK for stability would it be closer, or
does it simply have too much soda to be a stable formula?
I am having more and more fun with the glaze testing instead of
frustration. I won't say it's all become clear as a bell, but I feel
like I've started to gain some intuitive understanding of the
materials and the color responses so I have more idea where I'm going
and how to get there. I hope to have more serendipitous results to
post soon.
-Ivy G.
Matthew Katz on tue 10 apr 07
Hi Ivy, I haven't had a chance to look at your second glaze yet, but I would
give the following variation on the first one a try.
As I see it, the problem is not from too much Strontium, as much as not
enough. In that The glaze had a RO/R2O of .50/.50. This is going to limit
the gloss region of the glaze. so I increased the ratio to .70/.30 which
gives a wider working range. This should also help a little with run-away
Lithium, too.
Neph Sy
25.56 Strontium Carb 24.44 Lithium Carb 3.33 Whiting 6.11 OM4 15.00
Flint 23.33 3134 2.22 SiO2+B2O3/Al Ratio Alkali Metals Alkali Earths
5.43 :1 0.22 0.78 SiO2 B2O3 Al2O3 3.15 0.58 Li2O Na2O K2O 0.17
0.05 MgO CaO SrO BaO ZnO Fe2O3 0.01 0.77 0.00
On 4/9/07, iglasgo wrote:
>
> I'm having endless fun testing glazes, so I thought I'd post a couple
> of them. I've also posted a couple photos at
> http://outinmonument.blogspot.com/
>
> I'm working on getting a perfect copper blue for some tiles I'm
> making for my in-laws... Food safety per se isn't necessary, and the
> crazing is not a problem, but the glaze needs to be durable enough to
> stand up to my MIL's cleaning regimen. I tested my Cone 04 formula and
> it's just not durable enough.
>
> So I decided to try for a Cone 6 copper blue to match the low-fire
> glaze. What did I get myself into... After what seems like a
> million tests & recalculations I have arrived at this formula.
> The color is absolutely perfect. Gorgeous, deep, exquisite. Just a
> tiny bit of brown where it breaks on edges. The surface is a smooth,
> tactile dry matte with a few sugary crystals. Crazed, but not too
> crazed. It runs like crazy. But the color, oh, it is so delicious, and
> it is durable enough that it is not harmed by 36 hours in vinegar.
> Someone else might find this glaze to be perfect for their
> use. The only problem for me is that I really want a glossy glaze
> that doesn't break too much or run.
>
> Here's the recipe & analysis:
> My copper blue so far, ^6 ox.
>
> Nepheline syenite 46
> Strontium carbonate 19
> Lithium carbonate 6
> Whiting 3.5
> Kentucky OM #4 2.5
> Silica 19
> Frit 3134 4
> Add:
> Copper carbonate 5
> Cobalt carbonate 0.025
>
> Na2O 0.23
> K2O 0.06
> CaO 0.14
> Li2O 0.22
> SrO 0.35
> Al2O3 0.30
> B2O3 0.04
> SiO2 2.24
>
> So obviously this glaze is really high in strontium which I guess is
> what's making it matte. I have tried a version with more silica which
> did make it more glossy but also turned the glaze to a typical green
> color. Omitting the lithium made it less runny but also hurt the
> color. So I don't know where to go from here in trying to make it do
> what I want it to do. Would adding EPK stiffen it up without hurting
> the color response? Any other ideas?
>
> The other glaze I'm perfectly happy with the color and surface, but I
> don't know if it would be considered stable or not. It was a very
> unexpected result of a line blend of my cone 04 copper blue glaze and
> a cone 8 high calcium glaze. It has a nice semi-gloss surface, though
> it is heavily crazed.
> It is a light blue-green where thin, and deep green where very thick.
> Where it is medium thickness it appears like there's brown, almost
> metallic copper colored crystals floating on the surface. The overall
> effect is kind of like a mysterious, swampy bayou.
>
> Here's the recipe & analysis:
> Copper brown, ^6 ox.
>
> G-200 feldspar 27
> Nepheline syenite 16.5
> Whiting 19
> Strontium carbonate 3
> Soda ash 7
> EPK 5.5
> Silica 17
> Frit 3134 5
> Add:
> Copper carbonate 3
>
> Na2O 0.29
> K2O 0.10
> MgO 0.00
> CaO 0.55
> SrO 0.05
> Al2O3 0.28
> B2O3 0.04
> SiO2 2.16
>
> My guess from the numbers is that it's not stable, but I don't really
> know. Is it close? If I added EPK for stability would it be closer, or
> does it simply have too much soda to be a stable formula?
>
> I am having more and more fun with the glaze testing instead of
> frustration. I won't say it's all become clear as a bell, but I feel
> like I've started to gain some intuitive understanding of the
> materials and the color responses so I have more idea where I'm going
> and how to get there. I hope to have more serendipitous results to
> post soon.
>
> -Ivy G.
>
>
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>
--
Matthew Katz
Alfred, NY
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