Craig Martell on sat 22 feb 97
At 09:07 AM 2/21/97 EST, you wrote:
>----------------------------Original message----------------------------
>I have always had the understanding that if you need to reduce in an
>electric kiln, that silicon carbide would be the best for glazes. Has
>anyone experimented with using silicon carbide for Copper Reds in electric
>kilns yet?
Hi Leon:
I tried some reds using silicon carbide years ago and got some real variable
results. I experimented at cone 10 Ox. with reduction recipies and added
about .5 to 1.0% FFF silicon carbide powder. Triple F is the particle size
of the material and it is very fine. As you probably know the purpose of
silicon carbide is to produce a local reduction in the glaze to form the
red. On vertical pieces, I didn't have much luck and was only given small
spots of red in the lower parts of the pieces. From this I thought that
because the silicon carbide might be physically heavier than the other
ingredients, It will migrate to the lower parts of the pot and the rest of
the piece would be oxidized. I then tried the glazes on plates, tiles, and
low bowls with porcelain slips containing some copper, thinking that the
silicon carbide would settle in the glaze and contact the copper bearing
slips beneath. It seemed to work well and the results were a lot better and
I got some real passable reds.
One thought I had that I've never tried, is to ball mill the glazes with
silicon carbide to homogenize the particle size and make the FFF silicon
carbide even finer, and less likely to migrate downward on a vertical piece.
Perhaps the glazes need to be more viscous under melt to suspend the FFF
silicon carbide a bit better. You have to be careful of the alumina content
as in reduction, to achieve bright reds.
For what it's worth, Craig Martell-Oregon
Rick Sherman on sun 23 feb 97
For Leon:
Glad to find you experimenting with copper red reduction with silicon
carbide. For years, this was the way to get copper red in this
country and in Europe. Another way was to drip oil directly on the
pot during firing. If you can ever find it, get an index to the
Journal of the American Ceramic Society - back in the 20s. Craig
Martell from Oregon offers good advice. Be certain the silicon
carbide is very fine and suspended in the glaze when you apply it.
With some glaze bases, it will migrate to the bottom of the pot as
Craig describes. Sometimes its migration path provides a glaze that
goes from white to red and back to white in beautiful streaks. There
are lots of formulas. You can use as much as 1.6% copper carbonate or
as little as .40%. Try about .20% cupric Oxide instead. Silicon
Carbide can range from .26% to 40%. Try adding tin oxide, .40% to
1.5% and see if that helps. We experimented a lot in the 60s and
fired to ^9 and ^10 in a globar electric kiln. Have fun. RS
Marget and Peter Lippincott on sun 23 feb 97
Craig Martell wrote:
>
You have to be careful of the alumina content
> as in reduction, to achieve bright reds.
>
> For what it's worth, Craig Martell-Oregon
Craig:
I am interested in bright reds. Please describe the parameters of
successful alumina content.
Peter Lippincott
Mudpuppy Pottery
Craig Martell on mon 24 feb 97
At 10:29 AM 2/23/97 EST, you wrote:
>Craig:
>I am interested in bright reds. Please describe the parameters of
>successful alumina content.
>
>Peter Lippincott
>Mudpuppy Pottery
Hi Peter: "Successful", is really subjective in terms of copper reds, but
I'll do my best here.
For glazes fired between cones 7-10 Herman Seger sets the parameters for
alumina at 0.4-0.8 moles. Most copper reds are fired in this range, although
the color is achieved at lower temps than this. Looking at a few copper red
formulas, it seems that alumina can fall somewhere between .01 in some
chinese rouge falmbe' reds and .36 which is below Segers requirement of 0.4.
I guess I need to say before I go much further that I am not an expert in
the formulation or use of copper red glazes. I use one formula in limited
amounts and have good success but that's about it. As for bright reds, what
I really meant in regard to the alumina was to keep the clay addition to
copper reds low. This can be seen in most copper red receipes and formulas.
The red that I use has no added clay and the alumina is supplied only by the
feldspar and a small amount from Gerstley Borate. For brightness, Parmelee
suggests a 1 to 1 ratio of Tin Oxide to Copper and says that good reds are
possible without the Tin but in a lot of cases livery colors are produced
instead of brighter reds if Tin is omitted. The glaze that I use has 1%
copper carb. and 1% Tin Oxide, and 0.9% Red Iron. I have heard that Iron
may prevent the copper from being fugitive but I've never seen any real
solid information on this.
Again, for what it's worth, Craig Martell-Oregon
PJLewing@aol.com on mon 24 feb 97
The finest silicon carbide I've ever found at ceramic supply stores only ever
produced bubbles for me. I have had limited success with some 1000 mesh SC
that I got from an abrasives manufacturer. It's amazingly fine powder. So
fine you can't get it off your skin. It's much smaller than your pores. But
don't expect these to ever look like reduction reds. If you want it to look
like reduction, you've got to do reduction. Sorry.
Paul Lewing, Seattle
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