SBRANFPOTS@aol.com on sun 8 nov 98
> ----------------------------Original message----------------------------
> I have a 24" 10-sided soft brick raku kiln with 2 large venture burners
coming
> in underneath, i.e. the flame shoots straight upwards under the shelf. I
have
> four 3" holes cut on top (centered). I seem to be having problems getting
> enough airflow; I get some reduction going on during firing and have
trouble
> getting it up to temp. The shelf is elevated on half (hard) bricks. I have
> experimented with covering certain top holes (presently I fire with 2
opposite
> holes covered, which seems to work best). It is fired with natural gas.
> Anyone have any suggestions? Most of my work is raku-fired sculpture and I
> make my living (such as it is!) with my art. I sure could use some advice!
> Thanks so much for any help you can give.
> Karen
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To Karen and all,
The single most common and persistent question I get is about raku kilns not
reaching temperature or not being able to adequately control reduction. Proper
combustion is the result of enough air, Too much air is a far better problem
to control then not enough. In a raku kiln (or any kiln for that matter) air
enters the mix in 3 main places; through the burner (primary air) through the
flue (the holes in the top in this case) and around the burner through the
burner port. All three of these are easily controlled. Air also enters through
peep holes and any other spaces (between bricks, etc.) Also, this air must be
given adequate space to do its thing so there must be enough space between the
floor of the kiln and the shelf (average 9") and the draft must not be too
restricted by objects in the kiln, for instance a large bowl or plate stacked
directly under the flue opening.
There should be NO flame coming from the kiln unless you are purposly
reducing. Flame is always an indication of incomplete combustion (reduction)
The flame at the burner tip should be blue and strong. If your primary air
control is open and your flue is open and you still have flames then chances
are your flue opening(s) are too small. One large opening is far more
effective and easier to control then 4 smaller ones. This is a case of the sum
being greater than the parts! There should be at least a 1 1/2" space around
your burner for adequate secondary air. Leave the flue completly open and be
patient as you fire.
Hope this helps.
Steven Branfman
The Potters Shop
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