Kayo Parsons-Korn on thu 21 jan 99
Jeff Gertsch wrote asking some questions about pit firing. There are
probably many different answers to these questions depending on what
kind of effect you are trying to achieve. Do you want lots of colors and
flame patterns, or do you want to do blackware? Do you want something
really primitive looking or something with an incredibly high gloss?
>1. What kind of clay is best to start with?!? I am a novice and would
>like to start with some pre-mix bought at the university (ie c06-04)
>without having to alter it, or do I need something super low fire? I
>read in Hands in Clay that you can use anything from earthenware to
>porcelain (!), is this true? What is a best bet? I hope to start
>simple then get ambitious and dig some local up later.
You don't have to use low fire clay, but it should be something with an
open body so it can take the stress that pit firing puts on a piece. So
if you were going to buy pre-mix, maybe a raku clay would be a good bet.
Porcelain being so white would probably take on colors better. You can
spray it with copper carbonate or use natural materials in the fire like
seaweed or salt for flashings of colors. But I think it would be better
done in a sawdust fire where it wouldn't have so much stress. Gabriel
Koch mixes porcelain with T-mix to give it more strength. Her pots are
beautiful. Vince Pitelka has a recipe for a pitfire clay on a website. I
believe its Ron Roy's site.
Digging local clay can be ambitious. My husband has a new hobby of
digging up clay on our travels. Some have been great, and some need
a great deal of amendment. We recently brought some back from Northern
Arizona. After slaking it up and screening it to remove all the organic
stuff, rocks, etc. I poured it into a big plaster tub to evaporate away
the water. You wouldn't believe all the natural salts/minerals? that
precipitated out of the clay along the edge of the plaster. It wasn't
great clay, I think it had too much bentonite in it. But we once dug up
some clay near Sholow, AZ. that was wonderful. We were participating in
an archaeological dig and staying at a Forest Service Campground. I
didn't have the sieves to separate out all the junk, so I just picked
out the worst of it. It made a beautiful little pot. The little bits of
organic material left in the clay burnt out leaving these neat little
pits all along the surface.
>2. Which leads me to my next question: What range of temperatures do
>you see in pit-firing? I know this totally depends on your technique,
>but can you consistently hit 1000 deg C in a bonfire with a pit of
>modest depth and wood +cowpies+sawdust, or is this unrealistic? 500 >deg C? C
>Southwestern Native American, etc.) the better.
I've never measured with the pyrometer when firing. When I took Vince
Pitelka's Ancient Clay class, as I recall, he was estimating we didn't
get above the temperature we had bisqued at. Which was Cone 018 or 696
C. We had a rip roaring bonfire that probably went on for about 20
minutes. Which leads to another question. To bisque or not to bisque.
You will have better success rate (pots not cracking) if you bisque
first. But the higher you bisque, the less open the clay will be to
taking in carbon and if you are going for a high shine, it diminishes
with temperature. I just read an article about Nancy Youngblood Lugo and
she was dismayed by how many Indian artists now bisque their wares
before pit firing. In her opinion, if it cracks, it just wasn't meant to
be.
>3. Can anyone reccommend slips that can be used as a pseudo-glaze? I
>had heard of this somewhere. I assume true glazes are out of the
>question. Is there any way to waterproof a pit fired vessel (in a
>pit), or is the firing temperature too low? Maybe just kiln fire
>later.....
You can use terra sigillata, again check Vince's Recipe on the same
afore mentioned website. And there's lots of recipes for it in books. Or
you can just burnish the clay body with a smooth stone or spoon. This
would probably work really great with porcelain. If it needed to be
water proofed, you could use a sealer on the inside after firing. I
think people have been mentioning Jasco Tile Sealer. True glazes
wouldn't be possible. But you can get some of the same effects of
pitfiring from raku. Especially the blackware look, and then you could
line the pot with some sort glaze. If you refired in a kiln to glaze
temperatures after pitfiring, you would probably burn away all the cool
effects that you achieved through the pitfire.
4. Can anyone recommend literature on technical aspects of traditional
pit-firing techniques - books or periodicals?
Santa Clara Pottery Today
by Betty LeFree
ISBN 0-8263-0322-6
Talking with the Clay
Stephen Trimble
ISBN 0-933452-18-7
Sawdust Firing
Karin Hessenberg
ISBN 0-7134-7200-6
If you can get to the mainland, you might want to take Vince Pitelka's
workshop, Ancient Clay. I know he is doing it at the Appalachain Center
for Crafts in Tennessee and also at Michael McDowell's in Bellingham
Washington. Maybe somewhere else too. And there are always some classes
available in the Southwest on these techniques. Check Ceramics Monthly
or Clay Times workshop scheudules.
--
Kayo Parsons-Korn
Kayo Parsons-Korn Design
kayo@kayodesign.com
http://www.kayodesign.com
(503) 647-5464
P.O. Box 436
North Plains, OR 97133
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