Chris Schafale on mon 15 feb 99
Hey folks,
After trying a dozen or so iron red recipes for cone 6 ox, and
getting, essentially variations of brown, I looked at all the
recipes, and all the advice I'd been given, and came up with the
following:
Chris red
=========
KT 1-4 BALL CLAY.... 11.00 9.91%
SILICA.............. 34.00 30.63%
G-200 FELDSPAR G200. 11.00 9.91%
GERSTLEY BORATE..... 11.00 9.91%
TALC................ 11.00 9.91%
DOLOMITE............ 11.00 9.91%
BONE ASH............ 11.00 9.91%
IRON OXIDE RED...... 11.00 9.91%
========
111.00
CaO 0.43* 11.08%
MgO 0.32* 6.01%
K2O 0.03* 1.26%
Na2O 0.05* 1.38%
TiO2 0.00 0.16%
Al2O3 0.11 5.43%
B2O3 0.18* 5.65%
P2O5 0.08 4.95%
SiO2 1.92 53.39%
Fe2O3 0.14 10.68%
Cost/kg 0.42
Si:Al 16.68
SiB:Al 18.20
Expan 6.49
Tested it, and it is actually red. Not bright shiny tomato red, mind
you, but a soft, darkish red-brown matt. Nonetheless I was thrilled.
I fired it to cone 6, on the Slow schedule on my Skutt KM1027, with
a 30 minute hold and no special cooling at all. I have not tried it
on a slower schedule with extended cooling. I tried varying amounts
of RIO, and actually, more RIO makes this glaze blacker rather than
redder. A somewhat thin coat seems to work better than a thick one
-- it's sort of brown-green-gold where it's thick. Examined under 30x
magnification, it's a near-solid field of sparkly red crystals --
very cool. I tried the refire-to-bisque temp trick, and it doesn't
get any redder -- perhaps it has all the iron crystals it can hold
already.
Now, Ron Roy will take one look at the analysis and tell you it's
dreadful. The alumina is very low and the silica is pretty low.
It's oversupplied with magnesium. On the other hand, it doesn't run
(at least hasn't yet), doesn't craze or shiver, is unaffected by
soaking in either vinegar or dishwashing detergent for 3 days, and
passes the freeze/boil test. All there is in it to leach is iron. So
I hesitantly conclude that it's probably food-safe, though I can't
speak to it's durability under daily use -- I was able to mark it
with a steak knife, so you might not want to put it on dinner plates.
Good luck to any who give this one a try, and I'd welcome feedback
from any about questions of food safety, durability, etc.
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@nuteknet.com
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