Paul Lewing on mon 12 jul 04
on 7/12/04 11:08 AM, Chris Clyburn at chris_clyburn@COX.NET wrote:
> Is the
> difference great enough to warrant the wait and money, or can I substitute
> without running the risk of drastic changes. I know from Hamaer and Hamer
> that sodium shifts cobalt to more of a purple (one of the colors that i am
> looking for) and changes copper to more of a blue, unless of course I misread.
> The two glazes I am most concerned with follow:
>
> 43 matte med. purple
> Kona F4 (soda feldspar) 38
> China clay 4
> Bentonite 2
> Magnesium carbonate 17
> Whiting 14
> Zinc oxide 5
> Flint 20
> (+) Cobalt oxide 0.75
>
> and :
> 39 matte dk. blue-purple
> Kona F4 (soda feldspar) 70
> Bentonite 3
> Lithium carbonate 3
> Dolomite 7
> Zinc oxide 5
> Flint 12
> (+) Cobalt oxide 2
> (+) Tin oxide 5
Chris, the second glaze here, having nearly twice the feldspar as the first,
would probably be more affected by the switch than the first. But I think
the difference would be negligible. No way to know, of course, except to
test with both kinds.
In general, I'd say that the biggest influence on the colors you're going to
get from these glazes would not be from the feldspar at all. The second
glaze has a fair amount of zinc in it, which will affect the shades of blue
and green you'll get from cobalt and copper more than the difference in the
two feldspars. And the first glaze has a truly ungodly amount of magnesium
carbonate in it. No matter what feldspar you use, you're going to get a
lavender shade of blue from cobalt in that. Is this one of those crawling
glazes that beads up? I'd expect that to shrink enough to fall right off
the pot as it dries. If it were me, I'd reformulate that, and replace as
much of that magnesium carbonate with talc as I could get away with.
Paul Lewing, Seattle,
who came home from a backpack trip a day early last week because it was
snowing!
Chris Clyburn on mon 12 jul 04
I am curious how much of a difference using a potassium feldspar, such as
Custer, instead of a sodium feldspar, like Kona F-4, would make in a glaze
fired to cone 6. I have a series of test glazes I am planning to make and am
under severe time and money constraints. I have time to do one batch of
tests and I have custer feldspar available, but would have to order any of
the sodium feldspars. The order would cost more for shipping than the
material costs and the wait would cut my time margin very close. Is the
difference great enough to warrant the wait and money, or can I substitute
without running the risk of drastic changes. I know from Hamaer and Hamer
that sodium shifts cobalt to more of a purple (one of the colors that i am
looking for) and changes copper to more of a blue, unless of course I misread.
The two glazes I am most concerned with follow:
43 matte med. purple
Kona F4 (soda feldspar) 38
China clay 4
Bentonite 2
Magnesium carbonate 17
Whiting 14
Zinc oxide 5
Flint 20
(+) Cobalt oxide 0.75
and :
39 matte dk. blue-purple
Kona F4 (soda feldspar) 70
Bentonite 3
Lithium carbonate 3
Dolomite 7
Zinc oxide 5
Flint 12
(+) Cobalt oxide 2
(+) Tin oxide 5
Any help would be greatly appreciated.
Thanks,
Chris Clyburn
Mike Gordon on mon 12 jul 04
Hi Chris,
Are these glazes fired in Oxidation or Reduction? Electric or gas kiln?
Mike Gordon
On Jul 12, 2004, at 12:08 PM, Chris Clyburn wrote:
> I am curious how much of a difference using a potassium feldspar, such
> as
> Custer, instead of a sodium feldspar, like Kona F-4, would make in a
> glaze
> fired to cone 6. I have a series of test glazes I am planning to make
> and am
> under severe time and money constraints. I have time to do one batch of
> tests and I have custer feldspar available, but would have to order
> any of
> the sodium feldspars. The order would cost more for shipping than the
> material costs and the wait would cut my time margin very close. Is the
> difference great enough to warrant the wait and money, or can I
> substitute
> without running the risk of drastic changes. I know from Hamaer and
> Hamer
> that sodium shifts cobalt to more of a purple (one of the colors that
> i am
> looking for) and changes copper to more of a blue, unless of course I
> misread.
>
> The two glazes I am most concerned with follow:
>
> 43 matte med. purple
> Kona F4 (soda feldspar) 38
> China clay 4
> Bentonite 2
> Magnesium carbonate 17
> Whiting 14
> Zinc oxide 5
> Flint 20
> (+) Cobalt oxide 0.75
>
> and :
>
>
> 39 matte dk. blue-purple
> Kona F4 (soda feldspar) 70
> Bentonite 3
> Lithium carbonate 3
> Dolomite 7
> Zinc oxide 5
> Flint 12
> (+) Cobalt oxide 2
> (+) Tin oxide 5
>
>
>
> Any help would be greatly appreciated.
>
> Thanks,
>
> Chris Clyburn
>
> _______________________________________________________________________
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Chris Clyburn on tue 13 jul 04
--- In clayart@yahoogroups.com, Mike Gordon wrote:
> Hi Chris,
> Are these glazes fired in Oxidation or Reduction? Electric or gas kiln?
> Mike Gordon
Hi Mike,
The glazes are cone 6 electric oxidation.
Chris Clyburn
David Beumee on tue 13 jul 04
Chris,
Considering the spar content of both glazes in question, I would not substitute Custer straight across for Kona, speaking as one who has done fusion button tests on both spars.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> I am curious how much of a difference using a potassium feldspar, such as
> Custer, instead of a sodium feldspar, like Kona F-4, would make in a glaze
> fired to cone 6. I have a series of test glazes I am planning to make and am
> under severe time and money constraints. I have time to do one batch of
> tests and I have custer feldspar available, but would have to order any of
> the sodium feldspars. The order would cost more for shipping than the
> material costs and the wait would cut my time margin very close. Is the
> difference great enough to warrant the wait and money, or can I substitute
> without running the risk of drastic changes. I know from Hamaer and Hamer
> that sodium shifts cobalt to more of a purple (one of the colors that i am
> looking for) and changes copper to more of a blue, unless of course I misread.
>
> The two glazes I am most concerned with follow:
>
> 43 matte med. purple
> Kona F4 (soda feldspar) 38
> China clay 4
> Bentonite 2
> Magnesium carbonate 17
> Whiting 14
> Zinc oxide 5
> Flint 20
> (+) Cobalt oxide 0.75
>
> and :
>
>
> 39 matte dk. blue-purple
> Kona F4 (soda feldspar) 70
> Bentonite 3
> Lithium carbonate 3
> Dolomite 7
> Zinc oxide 5
> Flint 12
> (+) Cobalt oxide 2
> (+) Tin oxide 5
>
>
>
> Any help would be greatly appreciated.
>
> Thanks,
>
> Chris Clyburn
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
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