karen terpstra on fri 22 feb 02
Hi Brandon,
Here's my 2 cents worth.
> 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?
>
Draught from the chimney is crucial. If you can't pull the hottest part
of the flame through the chamber, you cannot reach temperature. I've
always read that the chimney should be about as tall as the length of
the kiln. As far as width, ours is about 3/4 the dimensions of the
firebox and then tapers to about 18" x18" toward the top.
> What should the proportions for firebox to chamber to chimney be?
>
That varies with kiln design. Ruggles and Rankin have a good design. I
can't answer without more info.
> What about the flu opening?
>
We made total square inches of the primary air openings equal to the
total diameter of the flue opening. The theory is: What goes in must
come out. It works for us and I've seen this method used on a number of
kilns. I think it is also mentioned in Jack Troy's "Woodfired Stoneware
and Porcelain" book which is the beginners woodfiring bible!
You didn't mention dampers. Are they passive? Mechanical? Do you have
both? It is necessary to have adequate dampers so you can adjust the
amount of draught through the chamber. Read about dampers and understand
how they work.
If you haven't already, read as much as you can about wood kilns AND
firing in general. Buy a few of the books; they are worth the
investment. My books and list is at school right now so I would spell
everything wrong if I attempted the list here. I really recommend
emailing Steve Branfman with the Potters Shop and
ask what he has available. Also the new one on woodfiring by Ceramics
Monthly...a collection of woodfire articles that have appeared in the
magazine. It's published by the American Ceramics Society. Go to their
website: for that one. (maybe Steve has that one
too?)
The wood mix that you mention sounds fine. You have to use what is
available to you and work with it. Once you reach temperature you will
know more about what effect it has on the work.
Be patient. Do the research. Ask questions. Ask Questions. Ask
questions. Someone told me once, "You won't know your kiln until after
at least 12 firings." I believe that all right!
Good luck and Happy Firings,
Karen Terpstra
La Crosse, WI
Tony Ferguson on fri 22 feb 02
Brandon,
Karen beat me to you. I was gong to say:
1. you need to have a stack that is powerful enough to draw your flame
through your kiln.
2. My dad, an engineer, said, like Karen, what goes in must come out in
terms of surface area and flow. This is a good rule of thumb to go by when
it comes to how your are dampering your stack if your stack is big enough..
If you stack isn't big enough to begin with, this won't matter. So, you
will have to build that stack taller maybe wider and keep trying. My first
firing in my wood kiln was to cone 8 with a 1 foot stack above the arch of
the kiln (there were no plans for my Anagama. According to the rules,
you're not supposed to be able to reach that kind of temp with my stubby
stack. Rules are meant to be broken BUT I had to make my stack about 4 feet
above the arch of my kiln and a bit wider. That did the trick--3 firings to
figure that out. I damper my kiln with kiln shelves that affect the actual
flame exiting space of the stack (at the top of the stack). I don't know
where you're dampers are but if you have enough stack you can always slow it
down with a surface area damper (like a sliding kiln shelf) or passive
dampers (sliding bricks in your stack that let outside air into the
stack/cool it down--these don't seem to make a difference with my anagama).
If you send some pictures of your kiln, stack, that would really help us to
help you.
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