GURUSHAKTI@AOL.COM on tue 13 jun 00
Dear Gerard:
Here's another version and a variation of it listed at the bottom of the
page. In this one I tried to up the magnesia a bit more than the first
revision and keep the silica the same as the original but up the alumina a
bit. The ratio is lower (12.85) than the original that you posted. I kept the
boron very close to the original and again, upped the Spar to get some higher
expansion material in there, other than the whiting. Upping the spar brought
in the extra alumina. I didn't want to lower the clay content any lower than
shown, but the alumina at .22 may work OK.
Randy's Red My Revision B
29 SILICA
33 G-200 FELDSPAR
30 GERSTLEY BORATE
4 EPK KAOLIN
7 TALC
5 WHITING
----------
123 Total
ADD: red iron oxide 15
I can redo it for you as 100% if you want. You'll just have to deal with all
the decimals.
FOR COMPARISON:
ORIGINAL RANDY RED REVISION B
Cao 36 .50
Mgo .46 .26
K2O .07 .11
Na20.11 .13
Al2O3 .18 .23
B2O3 .38 .37
SiO2 2.96 2.96
Another version you can try is use version 2, but up the silica to 29.6 and
lower the EPK to 1 and add 2 bentonite as part of the formula, not an
addition. This will keep up the ratio to 14.24 which is closer to your
original. It will also lower the Alumina to .21 which is closer to the
original, and ups the Silica a hair to 3. All the other equivalents remain
the same as Version 2. It will now total 107.6 without the 15% addition of
Iron Oxide.
Time to cook dinner!
Warm regards,
June
Paul Lewing on wed 14 jun 00
Gerard,
I've done more tests on this cone 5 iron red kind of glaze than probably
any other, and I'm a compulsive glaze tester. In fact, I use this
regimen of testing as an example of the kind of thing I go through when
I talk about testing in my glaze workshops. I'll bet I've done 300
tests on variations of this, so I've found out a few things about it.
First, forget trying to make this glaze conform to any kind of limit
formula. If you get it within limits, it won't be red. And my
experience with it tells me that if the Si:Al ratio goes below about 16,
it won't be red. The best veriations of it I've gotten heve had a ratio
more like 18 or 20. Here's another tip- the brand of iron you use makes
a big difference. The redder it is before it's fired, the redder it
will be after. It's also very touchy about thickness, what clay body
it's on, and especially cooling. It likes a slow cooling. Also, adding
a little tin oxide will help the red, and so will a bit of lead
bisilicate (yes, yes, I know).
Actually, I've abandoned this glaze in favor of one I developed that I
call Drop Dead Red. I call it Drop Dead Red because it's drop-dead
gorgeous, and because it's about 65% PbO. And, no, you can't have the
recipe. It's one thing for me to use it on my tile, but another to give
it out for general consumption.
Happy testing,
Paul Lewing, Seattle
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