Gavin Stairs on mon 20 sep 99
John,
Once again I congratulate you on insightful and useful work.
It would be useful to know more about the base glaze for this experiment.
It is possible that there is a relationship with other concentrations, not
only in the SiO2 and Al2O3, but also with fluxes. CuO might substitute for
Mg, for example (ionic radii 87pm vs 86pm, coordination number 2). Ca has
a much larger radius, but that is another possiblilty. And so on. Just on
the basis of the radii one might speculate that more copper could be
retained in a magnesium poor glaze than in a magnesium rich one. It might
be interesting to do some line blends in this way.
Gavin
June Perry on tue 21 sep 99
If a thin coating of clear glaze can keep copper reds from being fugitive it
might work to keep the higher copper content glazes from leaching. Have you
tried this?
Warm regards,
June
John Hesselberth on tue 21 sep 99
Gavin and others,
The base glaze I used for this experiment is a high calcium (virtually no
magnesium) mat to semimat:
Frit 3124 31.0
EPK 31.7
Wollastonite 23.2
Flint 14.1
Dark Rutile 5.5
Copper Carb. varied
It was fired to a strong cone 6 (cone 6 all the way down, cone 7 just
starting to bend)
Gavin Stairs wrote:
>----------------------------Original message----------------------------
>John,
>
>Once again I congratulate you on insightful and useful work.
>
>It would be useful to know more about the base glaze for this experiment.
>It is possible that there is a relationship with other concentrations, not
>only in the SiO2 and Al2O3, but also with fluxes. CuO might substitute for
>Mg, for example (ionic radii 87pm vs 86pm, coordination number 2). Ca has
>a much larger radius, but that is another possiblilty. And so on. Just on
>the basis of the radii one might speculate that more copper could be
>retained in a magnesium poor glaze than in a magnesium rich one. It might
>be interesting to do some line blends in this way.
>
>Gavin
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Ray Aldridge on tue 21 sep 99
At 09:43 PM 9/19/99 EDT, John Hesselberth wrote:
>----------------------------Original message----------------------------
I'd be interested in seeing the formula of the glaze you used in your tests.
Ray
John Hesselberth on tue 21 sep 99
June Perry wrote:
>----------------------------Original message----------------------------
>If a thin coating of clear glaze can keep copper reds from being fugitive it
>might work to keep the higher copper content glazes from leaching. Have you
>tried this?
>
>Warm regards,
>June
Hi June,
Yes, that can work. I tried it several months ago and have used it as a
crutch while I try to understand how to make the glaze itself stable.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Ray Aldridge on wed 22 sep 99
At 01:46 PM 9/21/99 EDT, you wrote:
>----------------------------Original message----------------------------
>June Perry wrote:
>
>>----------------------------Original message----------------------------
>>If a thin coating of clear glaze can keep copper reds from being fugitive it
>>might work to keep the higher copper content glazes from leaching. Have you
>>tried this?
>>
>>Warm regards,
>>June
>Hi June,
>
> Yes, that can work. I tried it several months ago and have used it as a
>crutch while I try to understand how to make the glaze itself stable.
>
But, doesn't this change the surface quality of the glaze?
I noticed that the glaze you tested bears a strong family resemblance to
the Insight matte. I've been working recently with a variant of that
glaze, recalculated to use 3134, and whiting and flint in place of the
wollastonite. (Yes, I'm cheap, but in my defense, I use a lot of glaze.)
It's a potentially great glaze that seems to defy the conventional wisdom
of limit formulas, and makes me wish I could afford the software.
If the funding were available for so many tests, something like Ian
Currie's volumetric blending approach to glaze development would yield a
lot of useful data. I think that's the sort of thing Gavin envisions the
International Clay Guild doing-- might be able to negotiate volume
discounts with a testing lab.
Ray
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