Joanne Van Bezooyen on tue 23 nov 99
I've just completed 3 successful natural gas firings in a row with my
little conversion kiln!
Oh! It feels soooooooo good!
I thank all of you who helped me to learn and understand natural gas
firing. With the proper tools and charts I was able to apply all of
your suggestions to 'get-it-up-there' and to kick a stall along.
I'm still working on initial slow heat....once I light the burners the
heat jumps fast....dangerous for bisque firings. With the principles
I've learned, however, I have confidence I can do it.
Thanks again,
Joanne in Tucson
Hank Murrow on wed 24 nov 99
>----------------------------Original message----------------------------
>I've just completed 3 successful natural gas firings in a row with my
>little conversion kiln!
>Oh! It feels soooooooo good!
>Thanks again,
>Joanne in Tucson
Group; Now here is great news! Wanting to fire her electric with gas,
Joanne asked us how best to proceed, bravely waded through the posts, tried
what made sense, and cheerfully set aside the remainder to fire her kiln
successfully. I count it as her triumph, as well as a triumph for the
ClayArt List! Happily, Hank in Eugene
"Orthodoxy is my Doxy. Heterodoxy is another man's doxy"
Bishop William Warburton in a letter to Lord Sandwich.
Micheal E Rector on thu 25 nov 99
Congratulations Joanne!!
I am glad to hear that you have been successful. I am also glad and
amazed that somebody can be taught to fire a gas kiln via e-mail.
Congratulations to the entire list and to you for that.
You seem to be concerned about keeping the rate of temperature rise down
in the early stages of a bisque fire. This and excitement over hearing
of your success has inspired me to write down some suggestions.
First off I would like to caution you about having ware hanging over the
edges of your shelves and into the flame. This causes part the that is
in the flame to heat up faster than the rest of the piece and crack,
discolor, or even explode. This is more of a problem the closer to the
flame ports you get.
Some people when firing electric kilns hold a piece of glass up to a
open view port to see if water condenses on the glass. If it does not
one concludes that the physical water has left the clay and it is safe
to turn up the heat. I do not know if this is reliable for electric
kilns (I do not do it). I know however that it is not reliable for gas
kilns. The products of combustion of natural gas are CO2 and Water, So
air coming out of a gas kiln is always moist. I tried it once, when I
was learning to fire. The kiln reached red heat 10 minutes after I
tried
this test, and at red heat it also failed the test.
I would not worry too much about the temperature of the kiln's
atmosphere climbing fast when you light the burners. It is the
temperature of the ware that is critical. One wants the temperature of
the ware to be under the boiling point of water but significantly higher
than outside the kiln for an hour or more depending on how thick the
ware is and how wet it is. As I am sure you know, this is so that the
physical water will be driven off before it has a chance to boil and
cause explosions.
Consider the roast you may be cooking on thursday. You will have the
oven at several hundred degrees F and it will take several
hours for the inside of your roast to heat up to the point where it is
considered done which is still lower than that of the oven. The same is
true in a kiln. I can not tell you how hot is too hot because I do not
use a pyrometer. However I can tell you that I have had kilns hot
enough for the air coming out of the flue to burn paper, yet still been
able to touch the ware with my bare hand.
The trick is to regulate the rate at which the ware heats up. I do this
by opening the kiln and touching the ware. It is a qualitative
measurement, but with a little practice it works rather well. If the
ware is hot to the touch, but I can still touch it comfortable for a
about two seconds, I consider the temperature to be about right. If I
can touch the ware indefinitely it needs to get hotter, and if I can not
touch it at all it is in danger of getting too hot. If you try this you
may eventually learn though experience what gas and damper settings work
for the rate of climb you want and not need to do it any more. Also
with a pyrometer you might learn to stabilize the kiln at a temperature
that works well.
To get a low flame that will heat the kiln up slowly I listen to the
sound of the flame. I light the burners and then listen for a change in
the sound as I turn the gas up or down. I turn them down until I can
not hear them. I call this setting a high candle. One can then turn
them down again until one notices a substantial change, or down until
the flame is barely there and then up again a little bit. This I call a
low candle. Unfortunately these are qualitative measurements. You can
make them quantitative if you have a gas pressure gauge that will
register pressures that low.
A low candle is generally safe to leave over nigh for slow drying of
ware. How fast and how much the kiln heats up can be regulated with the
damper, but with a low candle there is not much to regulate. A high
candle is another matter. Depending on the damper setting one can have
it heat the ware up very slowly over night or reach red heat and go into
reduction. If your damper is wide open it might not heat the kiln much
more than a low candle. A high candle is more versatile. If like me
you
do not candle over night and just want the ware to be hot but under 100
C for two or three hours a high candle with a moderate damper setting
should work well.
If your kiln is over powered, so that even a low candle is too much gas,
you can instal valves on the burners individually, and not light all of
them at once.
Good luck with your gas bisque. :-)#
Michael
Joanne Van Bezooyen wrote:
>
> ----------------------------Original message----------------------------
> I've just completed 3 successful natural gas firings in a row with my
> little conversion kiln!
> Oh! It feels soooooooo good!
> I thank all of you who helped me to learn and understand natural gas
> firing. With the proper tools and charts I was able to apply all of
> your suggestions to 'get-it-up-there' and to kick a stall along.
> I'm still working on initial slow heat....once I light the burners the
> heat jumps fast....dangerous for bisque firings. With the principles
> I've learned, however, I have confidence I can do it.
>
> Thanks again,
> Joanne in Tucson
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