Llewellyn Kouba on mon 23 aug 04
I would like to do some cone 6 clay bodies and glazes. Can I fire these in
my gas kiln. My electric kiln is too small for some of the larger sized
works. ( I am working on petitioning for a nice big oval Skutt or Olympic)
..I would think I coud just leave the flue open and it would be OK? I have
been told I should not try 04 majolica in my gas kiln also. I haven't done
so yet but would also like to try that....same reason. My electric is too
small. Maybe if I ruin something big that will help get my point accross
that I need a new kiln .
Thanks for the input in advance.
Llewellyn Kouba
Snail Scott on tue 24 aug 04
At 06:36 PM 8/23/2004 -0600, you wrote:
>I would like to do some cone 6 clay bodies and glazes. Can I fire these in
>my gas kiln.....I would think I coud just leave the flue open and it would
be OK?
A well-designed gas kiln will fire in oxidation,
no problem. But, some oxidation colors can be
badly affected by even traces of reduction at the
wrong time, so an oxyprobe could be helpful in
judging the correct damper and secondary air
settings. Or you can just guess, using a bit
more air than you would use in a reduction firing,
and keeping an eye on the kiln for errant signs
of reduction. Oxidation doesn't necessarily mean
dampers full open, though. You need to keep the
heat balanced and rising, too.
Some glazes are largely unaffected by reduction,
though, and some change but look nice that way.
Don't overlook the potential of ^6 reduction
firing.
As for majolica, remember it was all fired in
wood kilns back in the old days. It will take
a bit of practice to get the atmosphere right,
but don't give it up.
^6 in recent years has become almost synonymous
with oxidation firing, due to the rise in the
respectability of electic kilns, but there's no
inherent superiority in it. It's just different.
Many people fire ^6 oxidation because they have
no option but to fire electrically, but would
envy the opportunity you have to fire in any
atmosphere. ^6 reduction can be great! It seems
a shame not to take advantage of it.
-Snail Scott
Paul Lewing on tue 24 aug 04
on 8/23/04 4:36 PM, Llewellyn Kouba at lkouba@ASSUMPTIONABBEY.COM wrote:
> I would like to do some cone 6 clay bodies and glazes. Can I fire these in
> my gas kiln.
Yes, you can. However there may be some differences in the glazes and in
the firing.
Your electric kiln doesn't really fire in oxidation, unless you have one of
those vents that actually draws air through the kiln. Most electric kilns
fire in a neutral, or technically a stoichiometric, atmosphere. That means
there's just enough oxygen, no more, no less. In a strict oxidizing
atmosphere, there's really an excess of oxygen. But oxidation is close
enough to what an electric kiln does for all practical purposes. That's how
your glazes may differ.
Your firings may differ because your gas kiln may be tuned to fire evenly in
reduction, at least part of the time. Many people rely on a reduction cycle
to even out the temperature of their gas kilns, especially downdraft kilns,
at some point in the firing. This is especially true if their kiln tends to
have a cold bottom. You can get any gas kiln to fire evenly and efficiently
in oxidation, but you may have to adjust stuff like bagwalls, flue sizes,
gas pressure, stacking, or some such. Obviously, you're going to have to
set dampers and air intakes differently.
But you certainly can fire majolica in a gas kiln. The people who invented
it didn't have electric kilns. They didn't even have as clean-burning a
fuel as natural gas or propane, and they were able to do oxidation just
fine. Go for it.
Paul Lewing, Seattle
Ron Roy on wed 25 aug 04
Hi Llewellyn,
The atmosphere is never quite the same in a fuel buring kiln - compared to
an electric kiln - I don't know why but it could be the water that is
always present in a fuel kiln.
There are many oxidation glazes that will look very much the same - others
will change somewhat - you will find out. Just make sure you stay in
oxidation as much as possible.
Your main problem will be to get an even firing with the strong draft you
propose - perhaps slow down as much as you can afford to - give the heat a
chance to get around.
If something combustable - like a stick - will burn in the kiln it means
there is extra oxygen. I suggest you close the damper as much as you can,
use as little gas as you can and still get a decent rise - and check for
free oxygen.
RR
>I would like to do some cone 6 clay bodies and glazes. Can I fire these in
>my gas kiln. My electric kiln is too small for some of the larger sized
>works. ( I am working on petitioning for a nice big oval Skutt or Olympic)
>..I would think I coud just leave the flue open and it would be OK? I have
>been told I should not try 04 majolica in my gas kiln also. I haven't done
>so yet but would also like to try that....same reason. My electric is too
>small. Maybe if I ruin something big that will help get my point accross
>that I need a new kiln .
>
>Thanks for the input in advance.
>
>Llewellyn Kouba
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on fri 27 aug 04
Dear Llewellyn,
To get efficient use of fuel in a gas fired kiln (or when using any
other live fuel fired kiln) that is, the maximum calorific content,
there is a minimum quantity of air needed to supply the oxygen for
complete burning. Those who use modern Oxygen measuring devices can
make adjustments to their primary, secondary air and to the damper
setting to make this happens and promote a satisfactory rate of
temperature rise.
But without that instrument to guarantee an excess of Oxygen you need
to make sure you admit additional secondary air and ensure this is
mixed with fuel gases as they burn in the flame.
This can be achieved by either (1) enlarging your fire ports into the
kiln to admit more air, or (2) by moving the aperture of your burner
away from the fire port entry so that the flame entrains additional
air as it enters the kiln.
Encouraging a greater degree of draught may not be efficient. You
could sweep heat from the chamber before it has had time to soak into
your pots. When I build a kiln I always make the fire ports larger
than necessary in relation to the diameter of the flame. I can always
reduce those apertures if they admits more air than needed but they
are difficult to enlarge when not large enough.
Have fun.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.
John Britt on fri 27 aug 04
Dear Llewellyn,
Yes, you can most certainly fire oxidation in a gas kiln. You can also do
it in a wood kiln.
Good Luck,
John Britt
www.johnbrittpottery.com
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