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crystal firing in gas kiln

updated thu 15 may 03


Mark Cavassa on fri 9 may 03

I am a high school ceramics teacher, my classes are exploring the
possibility of crystal firing in a 10 cubic foot Geil Kiln (natural gas). I
have no practical experience with this firing type however have attended
lectures on the topic and read about the general process. As we do not have
a large window of time to tweek the process to perfection we are seeking
some expert advice concerning the following:

1. Most User-friendly Recipe(s)
2. Firing schedule
3. Any other info to assist us in a successful firing

(We will be doing one firing that will include about 25 pots.)Thank you for
your input.

Mark Cavassa

Dan Dermer on mon 12 may 03

Hi Mark-
I'm interested in this subject too... as many would say, a kiln is a kiln is
a kiln, so you could probably use many cone 8-10 crystalline glaze recipes,
and fire in oxidation/neutral along the same basic schedule as you would in
an electric kiln, with controlled cooling and hold periods on the way down.

If you're looking for glazes that develop crystals in a normal reduction
firing, there are quite a few recipes in the Robin Hopper book (Clay and
Glazes for the Potter) for matte crystalline types, which according to
Hopper's book, don't require a special cool-down like typical crystalline

Here is a recipe I found in Ceramics Monthly (Nov. '80) that you might try:

Whiting 8.8
Zinc Ox 27.6
Kona F4 45.3
Ball Clay 4.9
Flint 13.4
Black Nickel Ox 1.2 (I subbed Nickel Carb at 1.5%)
Bentonite 2

This glaze is a glossy, amber-ish celadon, a bit runny at a full cone 10
reduction firing, but developed lots of small, bright blue crystals on the
amber background for me -- very pretty! Nice subtle color on BMIX, and a
darker amber on stoneware clay, but same number of blue crystals. I fired
this in my normal reduction firing, but would *highly* recommend keeping
this glaze thinner on the lower half of the pot (it's a runner), and would
not soak at top temperature, but instead quick cool down to 1900 or so, and
hold for 45-60 min for crystals to develop.

There are also lots of places to look on the web for recipes; try some of
these: (clayart's crystalline glaze archive) (Lasse Ostman's site) (Fara's site)

Good luck, and share with us any cool c10 gas crystalline recipes that work
for you.

WHC228@AOL.COM on tue 13 may 03

I fire crystals in my gas kiln. It is not for everyone. I would expect a long
learning curve.
The problem is the same as any glaze that has a lot of zinc. If there is even
a hint of reduction in the kiln, the zinc burns out. This leaves you with no
crystals, and in their place a large number of sharp blisters.
If you try it make sure that you fire in excess air.
Bill Campbell