Craig Martell on wed 17 dec 97
Hi:
I tried this at cone 10 Ox. sometime back. There was nothing that I could
do to get good consistent reds on more vertical pieces. I think this was
due to the silicon carbide being affected by gravity. Copper red glazes are
usually very low in alumina for color development purposes so they are non
viscous and quite runny sometimes which would contribute to the silicon
carbides downward migration in the molten glaze. I then tried tiles and
shallow bowls and plates with a 1 to 2% copper slip, thinking that if the
SiC was "sinking" it would contact the copper slip and produce a better red.
It worked. I got the best reds that I could have gotten in oxidation on
these pieces. They were still no match for reduced reds, but they were
really not bad.
People doing Ox firing can get pinks, purples, and reds with chrome tin
stains, and additions of chrome and tin oxide to glazes. They are much more
consistent than copper reds in ox. or red. too. Once you get the glaze
bases worked out that are receptive to chrome tin stains, you're cooking.
An advantage to chrome tin reds in Ox too is no bubbling and pitting that is
usually associated with SiC reds in Ox. Chrome tin glazes need a fair
amount of Calcium to work. I usually used whiting and fluorspar. Watch the
amount of fluorspar though because it has fluorine which gasses and
sometimes causes pitting. I usually used about 5% and had no trouble.
Lithium (I used petalite) aids chrome tin reds as does barium. I never did
try subbing strontium but I have a feeling that it would produce reds too.
Anyway, you might give some of this stuff a whirl sometime. And remember,
we can't get chrome tin reds to work in reduction and that really bums me
out!!! I can't get the copper glazes to work half the time in reduction
either.
test, test, test, Craig Martell-Oregon
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