Fredrick Paget on tue 21 aug 01
I have heard that tungsten oxide acts as a surfactant in glazes.
If Karl Platt is still monitoring he could steer you in the right direction.
>Hello,
>
>I was looking to use as a glaze material a mica product mined
>and processed locally and got a puzzling result at cone 5 elec.
>
>Some areas are smooth matte, but large swaths are covered
>with bubbles and sharp-walled craters (bottoms of craters
>are very high gloss).
>
>I'm wondering about the mechanics of the bubbles. I assume
>that the bubbles are due to a high surface tension in the
>molten glaze at the same time there is a lot of outgassing.
>
>What factors increase the bubbling and/or diminish it? I
>can see a future both for the matte if I can produce it
>reliably and for the bubbly part as one of a two-coat system.
>Test glaze is:
> 4.5 WHITING
> 41.0 FRIT 3134
> 50.0 PM 325 (Polymica 325 mesh)
> 4.5 CUSTER FELDSPAR
> 5.0 IRON OXIDE RED
> CaO 0.61* 10.44%
> K2O 0.16* 4.56%
> Na2O 0.24* 4.52%
> Al2O3 0.47 14.59%
> B2O3 0.43 9.18%
> SiO2 2.64 48.85%
> Fe2O3 0.16 7.85%
>
> Cost/kg 41.83
> Si:Al 5.68
> SiB:Al 6.60
> Expan 8.70
>Polymica is:
> K2O 0.90* 8.43%
> Na2O 0.10* 0.62%
> Al2O3 2.80 28.40%
> SiO2 9.40 56.18%
> Fe2O3 0.40 6.36%
> Si:Al 3.36
>SiB:Al 3.36
>
>Any comments that bubble to the surface welcomed.
>
>Best
>Jeff
>
>Jeff Lawrence jml@cybermesa.com
>
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From Fred Paget, Marin County, California, USA
Jeff Lawrence on tue 21 aug 01
Hello,
I was looking to use as a glaze material a mica product mined
and processed locally and got a puzzling result at cone 5 elec.
Some areas are smooth matte, but large swaths are covered
with bubbles and sharp-walled craters (bottoms of craters
are very high gloss).
I'm wondering about the mechanics of the bubbles. I assume
that the bubbles are due to a high surface tension in the
molten glaze at the same time there is a lot of outgassing.
What factors increase the bubbling and/or diminish it? I
can see a future both for the matte if I can produce it
reliably and for the bubbly part as one of a two-coat system.
Test glaze is:
4.5 WHITING
41.0 FRIT 3134
50.0 PM 325 (Polymica 325 mesh)
4.5 CUSTER FELDSPAR
5.0 IRON OXIDE RED
CaO 0.61* 10.44%
K2O 0.16* 4.56%
Na2O 0.24* 4.52%
Al2O3 0.47 14.59%
B2O3 0.43 9.18%
SiO2 2.64 48.85%
Fe2O3 0.16 7.85%
Cost/kg 41.83
Si:Al 5.68
SiB:Al 6.60
Expan 8.70
Polymica is:
K2O 0.90* 8.43%
Na2O 0.10* 0.62%
Al2O3 2.80 28.40%
SiO2 9.40 56.18%
Fe2O3 0.40 6.36%
Si:Al 3.36
SiB:Al 3.36
Any comments that bubble to the surface welcomed.
Best
Jeff
Jeff Lawrence jml@cybermesa.com
John Hesselberth on wed 22 aug 01
Hi Jeff,
I'll start by admitting I'm going to be doing a little guessing on this one,
but I would offer a couple observations:
1. This glaze would seem to be significantly overfluxed for cone 5. The
combination of 0.4 KNa + 0.43 boron and relatively low silica tell me that.
Over fired glazes sometimes blister like you have described.
2. The variability could come from a couple different sources. Side to side
difference in heat history. If the bubbles result from overfiring were they
also right up against the coils? Secondly, how insoluble is the KNa
contained in the mica? I'm not familiar with mica, but if the KNa in it was
relatively soluble that could cause variable composition as you applied the
glaze.
I think my first step would be to fire another sample to about cone 2 and
see what happens.
Hopefully Ron or some others will chime in on this one and give you a more
informed analysis.
Regards, John
on 8/21/01 10:26 PM, Jeff Lawrence at jml@SUNDAGGER.COM wrote:
> Hello,
>
> I was looking to use as a glaze material a mica product mined
> and processed locally and got a puzzling result at cone 5 elec.
>
> Some areas are smooth matte, but large swaths are covered
> with bubbles and sharp-walled craters (bottoms of craters
> are very high gloss).
>
> I'm wondering about the mechanics of the bubbles. I assume
> that the bubbles are due to a high surface tension in the
> molten glaze at the same time there is a lot of outgassing.
>
> What factors increase the bubbling and/or diminish it? I
> can see a future both for the matte if I can produce it
> reliably and for the bubbly part as one of a two-coat system.
> Test glaze is:
> 4.5 WHITING
> 41.0 FRIT 3134
> 50.0 PM 325 (Polymica 325 mesh)
> 4.5 CUSTER FELDSPAR
> 5.0 IRON OXIDE RED
> CaO 0.61* 10.44%
> K2O 0.16* 4.56%
> Na2O 0.24* 4.52%
> Al2O3 0.47 14.59%
> B2O3 0.43 9.18%
> SiO2 2.64 48.85%
> Fe2O3 0.16 7.85%
>
> Cost/kg 41.83
> Si:Al 5.68
> SiB:Al 6.60
> Expan 8.70
> Polymica is:
> K2O 0.90* 8.43%
> Na2O 0.10* 0.62%
> Al2O3 2.80 28.40%
> SiO2 9.40 56.18%
> Fe2O3 0.40 6.36%
> Si:Al 3.36
> SiB:Al 3.36
>
> Any comments that bubble to the surface welcomed.
>
> Best
> Jeff
>
> Jeff Lawrence jml@cybermesa.com
>
Paul Lewing on wed 22 aug 01
Jeff,
Do you have any idea what the Loss on Ignition of the mica is? My guess is
that's where the bubbles are coming from. Have you tried calcining it
first?
Paul Lewing, Seattle
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