Dannon Rhudy on sun 24 may 98
I know this has been posted to the list before, but I ended up
with
too many requests (58 and counting) to post it privately.
Any kind of clay may be used for saggar/pit/sawdust firing. A
smooth bodied clay, without grog or coarse particles, lends itself
best to burnishing or terra sigillata. What color clay you choose
will determine certain things about the results you get. A dark
clay, such as terra cotta, will mute some of the firing results,
but can be very beautiful. Clay's will not reach more than a low
bisque temperature, so maturity is not an issue. I like to use
porcelain because it seems to take color so well, and burnishes
to a lovely sheen. But any clay you choose will work.
Prepare the pieces you want to fire. They can be anything you
like, handbuilt or wheelthrown, slab, coil - doesn't matter.
Large flat pieces will be prone to breakage because of the
nature of some ways of firing, (uneven heating.)
Burnishing: Burnished pieces are ready to burnish when leather
hard. Burnishing can be done with any smooth implement you like,
the back of a metal spoon, a polished stone, polished bone.
Burnish carefully, usually takes two or three times over the piece
to get a really smooth surface. Patience here will pay off later.
You can add a light coat of olive oil or lard to your surface,
burnish again - it will be very smooth. Let it dry.
Terra Sig: Don't use a burnished pot for terra sig; it is
redundant. Make some terra sig (recipes in books, CM, in the
archives of the list). The more trouble you take with the terra
sig, the quicker and better it will work. Wait until the pot is
bone dry, brush with a coat of terra sig. When that has dried to
the eye, you can add another coat, however many you think you
need,
just let the pot dry in between coats. Won't need more than 2-3,
depends on your terra sig. When final coat has dried, polish
with a soft cloth or a piece of grocery-bag plastic over your
finger. You will have a VERY slick surface. It polishes quickly.
Bisque fire your pots. (They can be fired as greenware, but many
will be lost to the uneven heat; I always bisque). I like to
bisque to about cone 012; some like a lower temp; some bisque as
high as cone 1. The higher your bisque fire, the less
smooth/glossy your pots will be. Experiment.
Now, you're ready to saggar fire, or pit fire, or sawdust fire.
Preparation of the pot itself is pretty much the same for each of
these kinds of firing.
For colorful results, you need to add a variety of combustibles
in and around your pots. I'll deal mainly with saggar firing
here, but the same information is useful in variation for pit
firing and sawdust firing.
The combustibles can be just about anything that you find or want
to experiment with. Various vegetable/fruit peels, grasses,
seaweed where available, very fine copper wire (engine rewinding
shops have wads of it, the finer the better). Dry manure, horse,
cattle, sheep, doesn't matter. If there is a fair ground or stock
yard nearby, it's a great place to collect it. But you can also
use the bagged stuff from the nursery; just be sure it is dry.
You can dissolve copper carbonate in water, or copper sulphate,
and dip your pots in it for a few seconds. Then let them dry. If
using copper sulphate, wear gloves, it is absorbed through the
skin. These can also be added in dry form to your "combustibles".
They sometimes produce really nice reds. Salt (table salt or rock
salt) adds good color in the orange-red range. Epsom salts
sometimes give lavenders. Very fine steel wool (XXXX) in sparing
amounts will give chocolate browns. If you use it too lavishly,
it will leave a rough surface on your pot. NOT soap pads; the
borax in them leave a blue glassy substance on the pot. Charcoal
and/or sawdust can give rich blacks.
I prepare mine this way: I place a bit of various combustibles
inside the pot. Then, I take a large paper bag, place some
combustibles in the bottom, put in the pot, fill the bag as full
of additional combustibles as I can and still be able to close
the bag. I fold over the top of the bag, use a piece of paper
tape (NOT plastic) to keep it closed. To make the saggar, I
do this: I take some clay slip from the slip barrel, a little
thicker than commercial paint. I dip sheets of newspaper into
the slip, and completely encase the bag the pot is in in SEVERAL
layers of the slip-coated paper. The paper saggar needs to be
completely sealed, so more layers rather than less are better.
If the saggars are well and completely sealed, you can fire the
pots in a gas kiln, and I often do student work in this way.
I line the shelves with dry newspaper, to keep the wet slip
from the shelf, and sit the pots inside, like stacking a bisque
kiln. I light the kiln right away, not waiting for the slip
to dry. I bring it up slowly for a couple of hours, then just
turn it up, let it fire to about ^012 or ^010. Get better color
at the higher temperatures. The inside of the saggars does
not reach that temp, probably a cone or so lower.
A few small pots, or one large one, can be fired in a raku kiln
in exactly the same way: light the kiln, fire a bit slowly for
a while; in the raku kiln, takes about three hours.
When the pots have cooled, the paper will of course have burned
away, and there will be a fragile clay shell around the pot.
Thinner than potato chips, and it will break very easily. There
is quite a bit of sweeping up after removing the pots, but it
is easily done. I began using paper saggars when I could not
figure out a way to do some very large pots in regular saggars,
or brick ones.
If you don't want to use paper saggers (not satisfactory for
sawdust firing) you can still prepare your pots in the same
way, leaving out only the slip-covered paper step. Then
immerse your bagged pots in the sawdust, light it, let it
smolder.
I do pit fires this way: prepare your pots (the paper bag is just
there to hold the combustibles next to the pot while you're
stacking your kiln/pit/barrel). I put a layer of wood and sawdust
in the pit, stack the pots in, and cover carefully with a LOT
of wood; I want the fire to get as hot as possible for a long
time. I light it, and when the mound of wood has burnt down
sufficiently, I cover the pit (a brick box above ground works too)
with a piece of sheet metal, to help hold the heat in. Usually,
it will burn all night or longer, take a day to cool. I have not
had problems with the weight of the wood breaking the pots,
just stack carefully, wood AND pots. DON'T USE TREATED WOOD!!!
Fumes are poisonous.
The cooler your firing, the more blacks and greys you will have
from smoke. The hotter, the less. Too hot, all the carbon will
burn out.
I know I left some stuff out, but this is getting WAY too long.
Dannon Rhudy
potter@koyote.com
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