Susan Towell on mon 5 dec 05
Hi all, my name is Susan and I am a potter in Northern Ontario (Thunder
Bay). I am a recent graduate of Sheridan College. I am a proud new owner
of an 18 cu. ft. Geil bricklined natural gas fired kiln. It arrived at
the beginning of Nov. and I've had two successful cone 10 reduction
firings thus far. In the Geil kiln manual it said I could reach cone 10
in 8-10 hrs. I don't know if they mean cone 10 reduction. I fired off in
13 hrs and 14 hrs. I'd like it to be 12 hrs or under. How long does it
take you all to reach cone 10 or what do you prefer? I understand that a
longer firing means richer glazes? Getting to my next question- At about
2000 degrees, there is a considerable amount of flame coming out the
chimney-is this normal? I realize the heat has to go somewhere, but if I
push the damper in anymore, the reduction is too heavy, and the temp. will
actually drop. Also. I fired today and it was -20, perhaps this is
another reason why it is not firing off as quickly. We had a similar
problem at Sheridan with the Bailey kilns and it would take us forever to
fire off-we didn't really care though cause we weren't paying for fuel. I
guess its that delicate balance of maintaining a good reduction while
acheiving an equally goo rise in temp. Otherwise the kiln has been
wonderful and I am happy with the results. I appreciate your time and I
hope someone can give me some feedback. Thanks, Susan
Snail Scott on tue 6 dec 05
At 10:53 PM 12/5/2005 -0500, you wrote:
>...In the Geil kiln manual it said I could reach cone 10
>in 8-10 hrs. I don't know if they mean cone 10 reduction. I fired off in
>13 hrs and 14 hrs.=20
The amount of reduction has a LOT to do with the rate=20
of heat rise, so I'd guess that the manufacturer's=20
estimate does not factor that in. Is your 14 hour firing=20
including candling? I find that I can shorten the effective=20
firing time (the time I'm there, watching the heat rise and=20
tending the kiln) by candling low, then high, so that there=20
is a gradual heat rise overnight and when I start the fring=20
'for real' the next morning, it's already got a bit of a=20
jump-start. I've never fired a Geil, and some kilns don't=20
give you much range of option for candling, but if you can=20
do that with yours, you can shut down your kiln in time for=20
a convenient bedtime. Though honestly, if I could fire in=20
14 hours at -20=BA, I wouldn't complain much.
If your glazes will allow an oxidation phase during most of=20
the heat rise, that will hasten the firing. Some glazes=20
can, but some won't.
>...How long does it
>take you all to reach cone 10 or what do you prefer? I understand that a
>longer firing means richer glazes? =20
Time at or around the peak temperature ('soak'), and=20
time during cooling, makes 'richer' glazes. Time during=20
that long middle heat rise counts for nothing much.
-Snail
Michael Wendt on tue 6 dec 05
Susan,
According to Ceramic Industry Magazine articles I have read, industry fires
in slight oxidation. My own experience with the oxyprobe shows that the
fastest rise rate seems to occur when there is only the faintest flicker of
flame coming out of the top of our kiln when viewed in a darkened kiln room.
I attribute the flicker more to turbulence than reduction. By 2000 degrees F
I see a "coronal" glow from the incandescent gases as they leave the flue.
If you have a chimney, the only way I can suggest to set your kiln to rise
more quickly is to follow these steps below.
Kiln settings are done this way after we are on full burner:
1) record current temperature on a white board every 20 minutes.
2) subtract the previous reading from the new one and record that difference
to the right halfway between.
3) adjust the damper setting to get the fastest possible rise rate. The
jumps are fairly large at first and gradually slow near cone 10.
4) when the kiln does stop rising, open the damper 1/8" and watch the
change. If the temperature drops, we tighten the damper gradually until the
rise rate climbs again at the fastest rate. The fastest rise rate happens
for us when the kiln shows no flame out the top but does show a "corona"
effect of very hot incandescent gas flickering out about 1-2".
I hope this helps speed your firings,
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
William & Susan Schran User on tue 6 dec 05
On 12/5/05 10:53 PM, "Susan Towell" wrote:
> I am a proud new owner
> of an 18 cu. ft. Geil bricklined natural gas fired kiln. It arrived at
> the beginning of Nov. and I've had two successful cone 10 reduction
> firings thus far. In the Geil kiln manual it said I could reach cone 10
> in 8-10 hrs. I don't know if they mean cone 10 reduction. I fired off in
> 13 hrs and 14 hrs. I'd like it to be 12 hrs or under. How long does it
> take you all to reach cone 10 or what do you prefer? I understand that a
> longer firing means richer glazes? Getting to my next question- At about
> 2000 degrees, there is a considerable amount of flame coming out the
> chimney-is this normal?
We've got a 24 cu. Ft. Geil natural gas kiln at school that we just started
using this semester. Have fired about 6 times this semester.
Our first issue was gas pressure from gas company. They only supply at
residential pressure (7" wci) or commercial pressure (2 lbs., about 56
"wci!). With the lower supply pressure, I could only get about 3"wci at the
kiln. Had them replace with 2lb. regulator, but then had to install an
additional 1/2" (14"wci) regulator to prevent damage to the Geil installed
regulator.
We now fire with top pressure of 4"wci! We get to ^10 in 9 -10 hours, and
that's with a very tightly packed kiln. Though Geil suggests a top pressure
of 6" wci, I found that too high and actually caused the kiln to stall.
You need to set your primary air (the disks on the burners) to an opening o=
f
2 popsicle sticks (laid flat) and just leave them at that setting all the
time.
The other thing I did was draw some additional marks on the damper. There
are lines etched into the damper and I simply drew pencil lines at 1/8"
increments between the etched lines. This gives me a very accurate
measurement for recording and repeating.
I start the firing with damper set at 2 1/2". As temperature goes up and ga=
s
pressure is increased, I open the damper more. At the end of the firing, th=
e
damper setting is 3 5/8" to even out temperature top to bottom.
Below 2000=B0F, I check the bottom spy hole for back pressure by holding a
piece of newspaper in front of it. If it burns, I have reduction.
First couple of firings, I relied on my knowledge of reduction firing from
the 1970's, lots of flame & smoke, very slow temperature rise. Now there's
no smoke, but plenty of reduction. So much so, that I actually have cut bac=
k
on body reduction after seeing black coring. We get great copper reds,
celadons and shinos.
Yes, there is a bit of flame from the stack, but I bet you're using too muc=
h
pressure and are closing the damper too much!
Let ma know if any of this helps.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Bruce Girrell on tue 6 dec 05
Susan Towell wrote
>At about 2000 degrees, there is a considerable amount of
>flame coming out the chimney-is this normal?
If flame is coming out the chimney it means that you are using too much fuel
(or too little air). While some excess fuel is necessary for reduction, you
want to use the minimum amount required. Flames in the chimney do nothing to
help heat your ware.
Recently I was experiencing hellaciously long firings (18+ hours) and was
starting to blame it on all sorts of things. I was using 10 PSI and even
higher gas pressures with the damper opened up to help draw more air to burn
all that fuel. The last three firings I have done at 3 PSI and they were
getting done almost too fast (<10 hours). My gas usage was cut in half.
Reduction was unaffected.
It sounds counter-intuitive, but turn down the gas.
Bruce Girrell
in snowy northern Michigan
steve graber on tue 6 dec 05
i bet the manual estimated times are for some typical 70°F or thereabouts room temperature. having -20°F rushing in while firing surly has the slowing affect you notice.
imagine trying to boil water with someone constantly adding an ice cube to the teapot?
i also doubt they included reduction time in the fire since so many people achieve reduction in different ways & to different levels.
i also wouldn't go about adding anything to the kiln (such as blankets, etc) without first calling giel kilns up to discuss your intent. they might say insure your kiln is not sitting in the blast of the north winds. have a wall nearby.
my kiln is a downdraft arch with burners firing up. i have a network of blocks in the foundation that also work as air pre-heaters (kind of like tunnels) to get the local fresh air from room temp to something higher before getting into the kiln. i don't live in cold country so i don't see a strong difference in firing from summer to winter. but i think you would.
if anything discuss with giel about the bottom of the kiln & ways to get the local air to pre-heat in some maner before entering the kiln. there is a lot of extra heat below the kiln that doesn't do much except heat up the ground. use this area to pre-heat the air. when room temp is 70°F, this may not be noticable, but with northern temps of -20°F to -65°F this certainly can be a fuel saving area.
see ya
steve
Susan Towell wrote: Hi all, my name is Susan and I am a potter in Northern Ontario (Thunder
Bay). I am a recent graduate of Sheridan College. I am a proud new owner
of an 18 cu. ft. Geil bricklined natural gas fired kiln. It arrived at
the beginning of Nov. and I've had two successful cone 10 reduction
firings thus far. In the Geil kiln manual it said I could reach cone 10
in 8-10 hrs. I don't know if they mean cone 10 reduction. I fired off in
13 hrs and 14 hrs. I'd like it to be 12 hrs or under. How long does it
take you all to reach cone 10 or what do you prefer? I understand that a
longer firing means richer glazes? Getting to my next question- At about
2000 degrees, there is a considerable amount of flame coming out the
chimney-is this normal? I realize the heat has to go somewhere, but if I
push the damper in anymore, the reduction is too heavy, and the temp. will
actually drop. Also. I fired today and it was -20, perhaps this is
another reason why it is not firing off as quickly. We had a similar
problem at Sheridan with the Bailey kilns and it would take us forever to
fire off-we didn't really care though cause we weren't paying for fuel. I
guess its that delicate balance of maintaining a good reduction while
acheiving an equally goo rise in temp. Otherwise the kiln has been
wonderful and I am happy with the results. I appreciate your time and I
hope someone can give me some feedback. Thanks, Susan
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Daniel Dermer on tue 6 dec 05
I wonder if you're using too much gas pressure... In
my own experience, my 16cf West Coast kiln fires
faster at 4.75 to 5.0" water column pressure (natural
gas) than at 6" pressure, which is the max for my gas
line. I seem to get more stalling or 'heat loss'
when I'm at max pressure in reduction, than when I'm
using slightly less than max pressure in my kiln.
I also switched recently to using higher pressure,
earlier on in the firings. For the first hour of a
glaze firing I'm firing at 1.5-2.0" pressure, and get
to about 500 degrees in the first hour. For the next
2-3 hours, I'm using 4-5" pressure to get up to body
reduction at 1600 degrees. That's a fast clip, but
I've had no ill effects, and it definitely reduces
the overall length of the firing.
This switch was based on advice from Clayart gurus
who point out that bisqued pots don't really care how
fast you get them up to reduction temperatures;
basically it's not necessary to candle or pre-heat
glaze firings.
-Dan
http://pages.sbcglobal.net/ddermer
Rikki Gill on tue 6 dec 05
I would just like to say that some kilns do that. I have an Olsen, I get
great colors, and yes, there is flame visible from cone 8 on. And it
increases in strength and color as the temperature climbs. I have been told
that the flame should be green, never red. When I tried that, no wonderful
color. The bottom line is that they all fire differently. Keep kiln notes.
Watch the air mix valves too. For me, they are the key to great color.
Best, Rikki Gill
www.rikkigillceramics.com
----- Original Message -----
.
> Susan Towell wrote
>>At about 2000 degrees, there is a considerable amount of
>>flame coming out the chimney-is this normal?
>
.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
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