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Appalachian Center for Craft Clay Studio
Vince Pitelka, 2009
Bisque and Glaze Firing in the Norman Updraft Kiln
The Norman updraft is great for bisque-firing and
low-fire glaze. It also works well for high-fire, but if you want the best
reduction effects, use the downdraft. This kiln has a hybrid burner safety
system installed 15 years ago by a local HVAC contractor to satisfy stricter
code requirements. In order to fire it successfully, you must carefully read and
follow the guidelines listed below.
Essential Guidelines Read Carefully!
 | Before loading, always check the burner ports and burner tubes for
obstructions. This kiln has an array of eight small venturi burners
mounted vertically beneath the floor in ports located around the perimeter
of the inside wall. If someones work broke or shattered during a previous
firing, fragments may have fallen into the burner ports and may be blocking
the burner tubes, and must be removed before loading the kiln. |
| Before loading, always check the pilot burners in each burner port to
see that they are lit. The safety system incorporates thermocouples
on all eight pilot lights connected to eight Baso switches (not Baso
valves). If any one of the pilots is extinguished, an electromagnetic valve
shuts off the flow of gas to all eight burners. If any one of the pilots is
not burning, get someone to press down the small lever/button on top of the
corresponding Baso switch and re-ignite the pilot with a propane torch.
Continue holding down the lever/button for at least a minute before
releasing. If no one else is around, you can use an alligator clamp to hold
the button down while you ignite the pilot. Check to make sure that the
pilot remains lit. |
| Use only the red-handle burner valve for burner adjustments. Do
not use the green-handle valve mounted on the vertical pipe, because it will
shut off the pilots as well as the burners. It is shut off only during long
periods of non-use or when we need to do maintenance on the kiln.
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| The damper adjustments indicated below refer to the width of the
opening when viewed from the front of the kiln. The left-hand segment of the
damper is never moved. The right-hand segment is supported with an iron
framework, and all adjustments are done on that side. |
| Make all gas and damper adjustments slowly. Quick adjustments
create a sudden change in draft that can extinguish one or more pilot
burners, causing the kiln to shut down. |
| After a preheat, watch out for carbon-buildup blocking the burner tubes.
For any type of firing, this kiln is generally heated overnight with the
main burners on very low, which creates a smoky orange flame originating
directly from the orifice at the bottom of the burner tube. Occasionally
this causes a buildup of carbon inside one or more of the burner tubes,
partially obstructing the tube and causing the flame to spill outside the
tube when you turn up the burners the following morning. If left in this
state, the flame will destroy the thermocouple and pilot burner. Immediately
upon turning up the kiln after a preheat, always get down on your hands and
knees in front of the kiln and look under the kiln to check the base of all
eight burners to make sure that there is no orange flame spilling around the
base of the burner. If you see an orange flame at the base of any burner,
you must remove the carbon. Beneath the kiln you will find a long piece of
thermocouple wire bent at 90 degrees at the end. Poke the bent end of the
wire up the offending burner tube and shake it around, dislodging the
carbon. |
| Close the damper completely at the end of a bisque-firing. Since
this is an updraft, it develops considerable convection within the kiln.
Leaving the damper open even a small amount at the end of a bisque-firing
will pull cold air into the bottom of the kiln very quickly, risking
thermal-shock cracks in the wares, especially large pieces. |
What To Do if the Kiln Shuts Off During a Firing
If you follow all the above guidelines religiously,
you should have no problems with the kiln shutting off by itself. Carelessness
in any of these areas can cause one or more pilot burners to go out, which will
cause all eight burners to shut down. In the case of carbon-blocking in the
burner tubes, the flame spilling around the base of the tube can damage valuable
components, necessitating downtime for repairs.
If the kiln does shut off during a firing,
immediately close the damper and the red-handle gas valve. Get the flexible
extension mirror from the instructor or resident, lay down on your side next to
the kiln, and with the mirror handle fully extended start checking each burner
from underneath to see if the pilot is still lit. When you find the one (or
more) that is extinguished, use an alligator clamp to depress the lever/button
on the associated Baso switch and re-ignite the pilot from beneath with the
propane torch. Do not pull the trigger button and ignite the torch until you
have it in place, because otherwise you run the risk of damaging thermocouple
leads or pilot gas tubes.
Leave the Baso switch depressed for at least a minute
before removing the alligator clamp, and then check with the mirror to make sure
that the pilot remains lit. Open the damper right before you turn the gas back
on to light the main burners. Remember to always adjust the damper and gas valve
slowly. This whole process is a royal pain in the neck to do, especially with
the two rear burners, which are very hard to reach with a propane torch. If you
ever have to go through this process, you will subsequently be extremely careful
about following all of the listed guidelines.
Bisque-Firing in the Norman Updraft Kiln
As stated above, before loading the kiln always check
to make sure that all eight burner tubes are clear and all eight pilots are lit.
For a standard bisque-firing, use cone packs with cones 09, 08, and 07 at the
top and bottom spyholes. When loading the first few levels of shelves in the
kiln, make sure that no wares hang out directly over the burner ports. When
possible, keep larger items away from close contact with the flames.
Bisque-Firing with Bone-Dry Work and No Very-Large or
Thick Work
| After loading the kiln, with the door still open, turn on the
fan switch next to the kiln, set the damper at 4", and turn on the main
burner valve (red handle) slowly until the main burners light. Observe to
make sure that all eight of them are lit. You may have to turn the gas up a
ways to get them to light, but then turn it way down so that there is just a
4"-6" orange/yellow flame emerging from the burner tube, but with no
pressure registering on the WCI gauge. Close and latch the door. |
| The next morning or after at least six hours of preheat turn
the burners up to ½" on the WCI gauge. As mentioned above, get down on your
hands and knees, look under the kiln from the front, and check all eight
burners to make sure that there is no orange flame at the base of any of the
burner tubes. If there is, use the bent piece of thermocouple wire and
remove the carbon immediately. |
| After one hour turn up the gas to 2". |
| After one hour turn up the gas to 3". If the top is
significantly hotter, close the damper to 3". |
| After two hours turn up the gas to 4". |
| When cone 08 is down close the burner valve (red handle) and
close the damper all the way. In cold weather, shut off the
fan switch. |
Bisque-Firing Very Large or Thick Work
| Sign up for a 72-hour slot, and load the kiln in the afternoon or
evening. Close the damper, close and latch the door, and let the
kiln heat gently overnight and through the following day with just the
pilot burners on. |
| The second day in the late afternoon open the door to make sure
everything is okay and to watch the burners light. Open the damper to 4" and
set the burners as described above to get a 4"-6" orange/yellow flame with
no pressure reading on the gauge. Observe the burners to make sure that all
eight are lit, and block the door open just a few inches to encourage more
air circulation through the kiln during the night. |
| The third day in the morning close and latch the door, and
follow the instructions above for the duration of the firing. Be sure
to close the damper immediately at the end of the firing. |
Low-Fire Glaze-Firing in the Norman Updraft Kiln
As stated above, before loading the kiln always check
to make sure that all eight burner tubes are clear and all eight pilots are lit.
Use proper cone packs at the top and bottom spy holes.
| An overnight preheat is not necessary, but its a good idea to
load the kiln in the evening, close the damper, close and latch the door,
and leave it like that overnight with just the pilots on. This should always
be done when the firing contains large work. |
| After the kiln is loaded but with the door still open (open the
door if you preheated overnight), set the damper at 4" and turn on the main
burners (red-handle valve) to ½" on the WCI gauge. Observe to make sure that
all eight burners are lit. Close and latch the door. |
| After on hour, turn up the gas to 2". |
| After one hour, turn up the gas to 3". If the top is
significantly hotter, close the damper to 3". |
| After one hour, turn up the gas to 4" |
| When your maturation cone is down, shut off the red-handle valve
and close the damper. In cold weather, shut off the fan switch. |
| After two hours, open the damper one inch. |
High-Fire Glaze-Firing in the Norman Updraft Kiln
As stated above, before loading the kiln always check
to make sure that all eight burner tubes are clear and all eight pilots are lit.
Use proper cone packs at the top and bottom spy holes, and if you are planning
an early reduction or body reduction, be sure that your cone pack is equipped
with an appropriate melt basin or tray to catch the melted cones. An overnight
preheat is not required, but without it, if you turn up the kiln at 8:00 AM you
will not finish until well into the evening. After an overnight preheat and an
8:00 AM turn-up, you will be done by late afternoon. Without a preheat, start
the kiln as directed but adjust the burners to ½" WCI and proceed as indicated
below
| After loading the kiln, with the door still open, turn on the
fan switch next to the kiln, set the damper at 4", and turn on the main
burner valve (red handle) slowly until the main burners light. Observe to
make sure that all eight of them are lit. You may have to turn the gas up a
ways to get them to light, but then turn it way down so that there is just a
4"-6" orange/yellow flame emerging from the burner tube, but with no
pressure registering on the WCI gauge. Close and latch the door. |
| The next morning turn the burners up to ½" on the WCI gauge.
As mentioned above, get down on your hands and knees, look under the kiln
from the front, and check to make sure that there is no orange flame at the
base of any of the burner tubes. If there is, use the bent piece of
thermocouple wire and remove the carbon immediately. |
| After on hour, turn up the gas to 2". |
| After one hour, turn up the gas to 3". If the top is
significantly hotter, close the damper to 3". |
| After one hour, turn up the gas to 4" |
| When the early/body reduction cone drops, turn up the gas to 6",
close damper slowly just enough to get a good orange flame at top and bottom
spyholes the opening will probably be about 1 ½ inches. Be sure to close
the damper slowly, and always avoid excessive back-pressure on this kiln, as
it can cause the pilots to go out. |
| After one hour of early/body reduction, turn the gas all the way
up to 9" and open the damper to 2"-3" to get a small flame at both spyholes.
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| When cone 10 is down, turn the gas down to 2" and open the
damper slowly to 4" for an oxidation cleanup. |
| After 30-60 minutes of oxidation soak, shut the red-handle gas
valve and close the damper. In cold weather, shut off the fan switch.
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| After two hours open the damper one inch. |
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