Rice on tue 4 mar 97
I have a question for anyone.
Recently I designed and built a raku kiln. The base is soft firebrick
sitting on a metal
cart-like thing that in turn sits on metal V-grove wheels- which in turn
ride along angle iron tracks. The kiln walls and roof are made from 4"
ceramic fibre held together by a superstructure of -get this- "hog fencing"
i.e. very strong mesh. The kiln is front loading and the door has holes cut
for the intake and exhaust. I am firing with propane using a raku flame
The kiln is excellant for raku - 20 - 25 minutes to reach 1900f.
The other day while looking at some of the disgusting crap glazes that only
an electric kiln can produce I wondered if my new raku kiln could reach
cone 6 temps - and fast - so that one day I would be delivered from
electric hell. Well today I put one little pot in my approx. 8 cubic foot
raku fibre kiln [which is a perfect cube] and blasted the sucker. I made
Mr. Cone 6 pray to Alla in 2 hours flat, plugged up the kiln and waited for
everything to cool. After about 7 hours I opened the door -the kiln was
still about 500f [who gives a shit it's only a test, right?] - and behold
!!!! what seemed to be a perfect looking cone 7 - 71/2 firing sugar bowl.
The glaze was completely and utterly done. I thought -oly shit cone 6-8
reduction firings in 2 hours - I've just discovered America!
Then I called a friend who has about a billion years of pottery experience
and told him about my findings. He immediately informed me that my pot was
probably trashed and would have a gijillion micro cracks and if I put some
boiling water into the test piece, it, and my house would probably explode.
What a piss off! So I heated the test pot up and then stuck it in cold
water. Nothing happened. Next I put the pot in the freezer. After a couple
of hours I will put boiling water in the frozen test and see if it cracks.
If this test works - the pot survives - I will probably do it a few more
So finally this is my question: What tests should I perform in order to
determine if this firing technique is viable? Has anyone heard of anything
like this and if so is there something I'm missing.
Pinch me I must be dreaming....
Jim Karavias on wed 5 mar 97
I'd check out the test for glaze fit that tony hansen recommends.
Two minutes boiling water, two minutes ice water. 5 or 6 cycles of
this and then check for crazing or other surface imperfections.
Seems like it might be glaze dependent. How much reduction does the
glaze like. How long a soak? Can you modify your glazes to work
with this technique? Is the piece evenly vitrified to the same
degree throughout its body? Will it burst into shards all by itself
3 months from now sitting on a shelf somewhere?
Cool experiment though. I wonder how it will work out?
Fay & Ralph Loewenthal on wed 5 mar 97
Fraser this sort of works when you have a relatively
empty kiln. I have done a similar sort of firing with
porcelain, firing to 1300C within 6.5 hours, and I was
taking it easy as the items were not bisqued. The cooling
took about 4 hours. It does not work every time and if
you want consistent results forget it. My porcelain
shrinkage was also > 20%, but was slip cast so I
suppose it is to be expected. I usually raku to about
1100C in my gas kiln and still get inconsistent results,
but I like excitement in my life and do not want the boring
same results evey time.
Enjoy life while you can Ralph
WardBurner@aol.com on wed 5 mar 97
Fraser Man---you ain't dreamin...
Most potters don't realize how fast they can fire if they so desire. They
were "raised" with the idea that cups of coffee and 2am lonely kiln vigils
are the only (and somewhat romantic) way to fire a kiln. Ain't so.
Industry fires commercial porcelain in a tunnel kiln. It goes in one end,
cold glazed bisque, and comes out the other cool fired porcelain. Time; 45
minutes. Wall tile (the stuff on your bathroom floors and walls) is fired to
stoneware temps. cold to cool in 10 minutes!
Now these folks have fired clay with probes in it hooked up to computers.
They know their clay. Firing is like driving on a toll road with no speed
limit. The toll booths of alpha to beta and cristobalite inversions demand
you slow down as you go through, but the rest of ther ride can be awfully
fast. Some clays and glazes can easily handle this treatment, some can't.
Most of the "look" of handmade pottery comes, not from a slow firing, but
from a slow cool down. In pottery kilns, because of construction techniques
and burner systems, slow firing and slow cool-down usually go hand in hand.
Because of this, most potters think that this is the only way to fire.
I've personally fired large kilns (60 cubic feet)to cone 9 in 45 minutes.
(you don't own a burner business and fired Raku for 25 years without being a
pyro). Have fun....
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
Rice on thu 6 mar 97
I have completed two more firings - both in just under two hours. In the
last firing I even got a COPPER RED - you heard right. I've talked to a
couple of specialists in the field since then and they tell me that
freezing and boiling and heating .... shocking the shit out of these pots
will indeed tell me if the body can handle the fast cycle.
Two concerns were raised about the quartz inversions that occur in the 500f
and 900f ranges. The latter is probably not a problem since cristobalite is
not excessive until high cones-[ this comes from someone who knows - not
me] and as for the former - well, I'll slow the firing down from 900-1100
to , hmm, say 20 minutes [heh heh].
In the last two firings I used a number of pieces - mugs, slab trays, solid
pieces of clay that a kid made etc. I used a stand-alone cone 6 on a shelf
and a cone 7 and cone 8 sitting on the floor. After the firing and cooling
Mr. Cone 6 was definately picking up the soap, and on the floor of the kiln
Mr. Cone 7 was kissing the pavement and Mr. Cone 8 -yes 8- was at half
mast! All the glazes were completely melted and I have not experienced any
I will give details of the kiln: I had a welder make a metal cart 35" X 34"
with 4"walls. The cart has four stationary v-grove metal wheels. The kiln
is built on this cart -and since the kiln is fibre ie not weather proof -
the kiln can be pushed along a track -made from inverted angle iron- into
one of those aluminum sheds. The kiln base is made from 2300 soft brick 2
bricks deep with a perimeter profile that looks like this:
| a | _____
| l | | |
| l | | |
| | | |
|____ | | |____
soft | __________________shelf________________
two layers of soft brick here
| _____________air flow____________________ |
| | | |
| | | | >-- out [penthouse]
| | | |
| | | |
| | | |
| | | |
| air flow | shelf | | <-- flame in [lower level]
| | | |
| | | |
| | | |
| | | |
| | | |>-- out [penthouse]
| |______________________________________| |
|__________________air flow_______________________ |
flame goes in base and exhausts out near top - and the right hand side of
drawing directly above is also the door - ie the the intake and exhaust are
built into the door.
side: | <-- [climbing kiln type of bag wall]
_> | ->
____ | _ > _>
| | _>
| | __________________________________
| <--- <-- <--mr flame
gee I should go into desktop publishing....
I will try slowing my firings down to 3 hours and continue to test the
pieces. Any advice or recommendations are greatly appreciated.
Next week I'm going to do a firing with two shelves and more pots - using
celadons, copper reds and other reformulated cone 11 killer glazes.
Now I have to get back to flight simulator95- where I have completely run
out of fuel over Toronto with 183 orphans and nuns on board at 3500feet. My
flaps will not extend and the only landing strip is the Island airport
which is only about 1/2 the necessary length. As you can imagine there is a
lot of screaming and puking going on so I better