Brandon Phillips on thu 21 feb 02
We completed our wood kiln on monday, loaded it up and fired it on
wednesday. The design is based on the rankin/ruggles climbing kiln, except
that this kiln has only one chamber. The firebox is exterior, buttressing
the cat arch chamber. We fired for fourteen hours getting stuck at cone 4
for about 6.5 hours before giving up. I think the problem lies with the
chimney, I think that the cross-section of the chimney is far too large for
the kiln. It is about 3/4 the dimensions of the firebox. I remember
reading once that the firebox should be 10 times that of the chimney
cross-section. Can anyone tell me if this has an affect on the firing?
What should the proportions for firebox to chamber to chimney be? What
about the flu opening? This is my first wood kiln and honestly I'm pretty
excited that I got to cone 4 without any problems. If it helps I was firing
with pine, cedar, oak and mesquite. Had no problems up to cone 4, steady
raise in temp. Any help that you could offer would be great!
Thanks!
Brandon Phillips
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Kathy Steinsberger on fri 22 feb 02
Hi Brandon,
I share a 2-chamber, "R&R"(Ruggles & Rankin)-type kiln
with Linda and Charlie Riggs (and some other folks) in
Carthage, NC. The chambers are 50 cu.ft each, with an
outside front-loading main firebox and smaller
side-loading ones in each chamber.. We fire with oak
and pine, adding salt and soda to the second chamber
only. We've fired 5 times and learn something new
every time. Most of us have fired a number of other
wood kilns, anagamas, mostly. But now we have our own,
and we know all about the stalling problem at
2000-2200! And the air flow problem, and the pots
jumping off shelves problem... About stalling, after
2000 degrees we stop looking at the pyrometer and fire
by cone to 10 or 11, just so we won't tear our hair
out too much... Irregardless, we love our firings and
the pots, and keep doing it.
Our 4th firing took 36 hours before we quit. We closed
the first chamber at cone 9-11 and second (salted)
chamber at cone 7 - 8. Nothing for an anagama, but
grueling when you're working with a short crew,
stoking simultaneously in 4 chambers...In the last
firing, we stopped following many of the documented
firing suggestions and winged it by leaving some air
ports on the firebox wide open and (lucky) maneuvering
the dampers throughout the firing. We shut down after
15 hours, yippee! Pots were pretty though I'd have to
check the logbook to remember the exact cones reached
(9,10?). A lot goes on with a 2-chamber kiln over 15
hours, and what specifically worked, who knows, but I
know this time it worked... Charlie, are you out
there? Linda, help?
After our first firing, (22hrs and underfired) some of
the kiln members also suspected we might need a taller
chimney, but instead we changed some less drastic
things. Thank goodness! These might help you.
This included wood type- we added more pine to the
initial oak as "red heat" occurred and cones started
dropping; We adjusted wood size for combustion
conditions- decreased diameter gives hotter, faster
burning; thicker pieces give slower, cooler burning. I
don't know if I've worded this well, but, you have to
"read" the combustion by watching the flames in the
firebox and smoke color and thickness in the chamber
and chimney, then manipulate stoking and dampering to
regulate oxidation, reduction, and neutral conditions
for your needs. Perhaps you are already doing this,
then forgive my simplifying...
We like to let Charlie wrestle with the dampers. He is
very good at using the passive and active dampers to
regulate air flow in the kiln. Irregardless of who
adjusts the dampers, we like to discuss every small
change and then have Linda write it in our log book.
Adjusting the dampers is really important for our
kiln.
Air flow is also affected by loading, so you may want
to experiment with that too. We find our kiln draws
like crazy now, causing pots to go tumbling off the
shelves if we aren't careful in stoking. The suicide
mugs, which are uaually mine, are pretty light. I set
them in a more protected location now...behind one of
Charlie's big pots, not in front of the firewall.
I think Charlie may have changed something about the
firebox, but I can't remember, maybe he can add to
this discussion...Oh yes, we also add little pots or
pieces of shelving to the firewall spaces to deflect
heat and slow heat movement up the chimney...
I fired a simular 2-chamber kiln (we built it, then
fired it) at the NC Pottery Center with Will and
Douglass last year and Will drives that thing very
tight! We were loading in a very precise way,
measuring every pot and placing exact to Will's
specifications. Then during firing, counting wood
pieces loaded, having pre-measured them to the inch,
adding "adjustors" (short, fatter wood pieces) to low
combusting sides, and always adjusting the dampers,
and sometimes the sheet of metal over the chimney
cap.. It was a first firing for the Seagrove kiln, and
a little dry, but we were done in 18 hours and pots
were really very nice! Repeating those steps for our
kiln didn't work...
Extraneous air flow from doors, stoke ports, and
firebox vents can also bring cool air into the kiln or
let heat out. Will was very concerned that we muddied
up the door walls totally. When stoking at red heat,
we open & close stoke ports as fast as posible, and
simultaneously. Even 1/4 inch peek holes between the
stoke port bricks are avoided by angling the bricks.
We put cone packs throughout the kiln and notice a
wide variation in temperature and heat absorption
depending on how we are "driving" the dampers. The
door side is usually cool, sometimes appearing
stalled, while the back side flies like a dream; the
top may be cold, while bottom is droppping cones every
30 minutes! then we go to the active damper and adjust
an inch in or out, depending on what we need. Our
biggest problemm is waiting the hour or so for the
kiln to adjust! There are typically cold spots and hot
spots we wrestle with every firing, but sometimes they
switch!...)
These types of kilns loose heat really quickly, which
can contribute to the apparent stalling effect. The
Studio Potter articles by Ruggles & Rankin in the
early 90's have been invaluable in explaining the
theories, but eventually we had to learn to read our
own kiln. We're still learning.
Perhaps Charlie or Linda can give you a little more
advice and more accurate information on what we've
tried and learned. Each kiln is different, though, and
you will have the joy of acquiring your own set of
firing criteria!! Also, everything I've said is only
what we've learned by firing our kiln, it may not work
for others and amazingly might be exactly opposite
from expected results and theories...which is why it
took us 5 times to try it!
We have a firing planned for late April and you are
welcome to campout and help fire it. You can call me
at 412-361-4267 or email my home email account at
ksteinsberger@yahoo.com.
Good luck and blessings on your next firing, how do
your pots look this time?
Kathy
Recently moved to Pittsburgh, but my heart is still in
NC.
Kathy Steinsberger
Freewheeling Pottery
5817 Holden St.
Pittsburgh, PA 15232
or 7909 Tulip Circle
Raleigh, NC 27606
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