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FIRING A KILN WITH A DOWNDRAFT VENT
Downdraft vent systems not only remove dangerous fumes during firing, they
also increase oxygenation of the firing chamber, reduce the variation of heat
in the kiln, and aid the cooling process. With a downdraft vent system in
place, the lid stays closed and the peep hole plugs remain in place during
the entire firing, which means you don’t have to worry about touching a hot
kiln to shut the lid and put in the peep hole plugs. Venting of any method
is strongly recommended in most situations.
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Quick Hint |
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A little kiln wash dabbed on the top of new cone supports greatly
reduces the chance of a cone sticking to the new metal. |
- FIRING BASICS
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All kilns are different, and every firing is different, depending on
density of load, weather conditions, kiln and element conditions, and
many other factors. This firing schedule is intended to be used as a
guide and should be adjusted to your own unique firing situations. Some
people will find better results by staggering the times the switches
are turned up (i.e. at step 4 on the bisque firing, turn the second
switch to low, then 30 minutes later, turn the third switch to low).
We recommend when altering this, or any, firing schedule, you adjust
one variable at a time so if something goes wrong, the problem is
easily identifyable. We also recommend keeping a firing log and the
fired cones as a record of your firings. Regular preventative
maintinence is also suggested. Checking the kiln sitter with a firing
gauge, vacuuming the firing chamber, kiln washing shelves, and checking
how evenly the kiln is heating by placing witness cones on the shelves,
should all be done on a regular basis.
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Quick Hint |
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The timer is a back-up device that will shut off a kiln to prevent an
overfire if the sitter malfunctions in any way. Sitter malfunction
can be caused by neglecting to adjust the sitter, interference that
restricts movement of the sitter mechanism, and normal wear on the
sitter parts, which degenerate by exposure to heat, oxidation, and
glaze fumes (primarily the tube assembly, sensing rod, and cone
supports). |
- THE BISQUE FIRING
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1)Place a junior cone 03 (“sitter” or “small” cone) in the sitter as
you load your kiln. Many people forget to put the cone in the sitter as
they load the kiln, but once they do, they rarely forget ever again!
2) In the evening, set timer to maximum time, then turn on bottom
switch ONLY to low. This process may also be done over several hours
before firing. The vent should be on, but it isn’t necessary at this
point. This phase of “preheating” helps to slowly remove moisture from
your pieces. This is an extremely critical point of firing. Water
turning to steam expands 1,170 times, and if the water in the clay
turns to steam too fast, the piece can blow up. Even though your pot
may feel totally dry, there is still moisture in the clay.
3) The next morning, reset the timer for 30 minutes - 1 hour longer
than the firing time and turn all switches to low for 3 to 4 hours. If
you don’t already have the vent on, turn it on now.
4) Turn all switches to medium. Leave at medium for 3 to 4 hours.
5) Turn all switches to high. Given all variables, a good estimate of
the remaining firing time at this point (from when you turn the kiln up
to high to when the sitter shuts off the kiln) is approximately 2 -
3 hours. The vent stays on during the cooling process.
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Quick Hint |
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A firing gauge is necessary to periodically check the accuracy of a
kiln sitter. The firing gauge is a metal disk with a hole in the
middle and two notches on the perimeter. For easy access and storage,
un-bend a paperclip slightly, insert it into the hole on the firing
gauge, and hang it from the lid hinge-pin on your kiln. To check the
kiln sitter, put the gauge on the tube assembly inside your kiln
(where a junior cone would usually be placed). Adjust the set-screw
on the outside of the kiln sitter until the claw holds the metal
plate in place. |
- THE GLAZE FIRING
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1) Place the junior cone appropriate for your particular glaze firing
in the sitter as you load the kiln. Again, people generally forget
this step only once. Preheating is not necessary in this stage.
2) Set timer for 30 minutes to 1 hour longer than the firing time and
turn all switches to low. Turn vent on. Leave switches on low for 3 to
4 hours. (Many people prefer to start a little slower by turning the
bottom switch to low, then 30 minutes later turning the other switches
to low.)
3) Turn all switches to medium, leave at medium for 3 to 4 hours.
4) Turn all switches to high. Given all variables, a good estimate on
firing time from when you turn the kiln up to high to when it shuts
off is approximately 3 hours for a low-fire glaze firing. Higher cone
firings will increase the firing time by an average of 15-30 minutes
per cone number. The vent stays on during the cooling process.
- This page was last updated:
Sunday, December 4, 2005 11:51 PM
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