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FIRING A KILN WITHOUT A DOWNDRAFT VENTING SYSTEM
In many situations, a vent system is not necessary. Good ventilation via
doors, windows, garage doors, and similar structural openings is adequate to
disperse fumes that are produced during firing. Fume reduction can also be
aided by a fan which pulls air out of a room or a hood-style vent. However,
if a room is to be continually occupied during firing, a vent system specific
to kilns is recommended to directly remove fumes before they can circulate
through the room.
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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
second switch to low, then 30 minutes later, turn 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 junior (kiln sitter) 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. Peephole plugs should be out, and the lid should be propped open. 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 timer for 30 minutes - 1 hour longer than firing time and turn all switches to low for 3 to 4 hours. Leave the peephole plugs out and the lid propped until you turn the switches to medium.
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 on 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.
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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 firing time and turn all switches to low. Peephole plugs should be out, and the lid should be propped open. Leave switches on low for 3 to 4 hours.
3) Put peephole plugs in and close lid. 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.
This page was last updated:
Sunday, December 4, 2005 11:50 PM
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