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ClayArtsUtah

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Originally Posted on: Mar/16/2005 9:31 by Dawn
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Updraft Gas Kiln to Cone 10: A Firing Blog
 
I am staring at a new Olympic Gas Kiln recently installed at Pioneer Craft House. As the adult community education teacher 7 weeks into the class, I have to learn to fire this thing and get work from 20 students through it in the next three weeks. Seemed like a great opportunity to blog the learning curve on this puppy.

Note that an electric kiln was installed next to it which is also intended for high fire. I have blogging that frustrating experience in “My Adventures Firing an Electric Kiln to Cone 10.”

Of course I started by getting the manual. This was an adventure in and of itself because everyone was afraid the manual would be lost and, therefore, no one could find it. I finally managed to get a photocopy. I highly recommend making multiple copies of your manual from day one. Before even firing the kiln, I have made notes all over my copy. If it turns out my notes are wrong, I would hate for this copy to be passed along to another person.

This is terrible to say, but I was surprised at how helpful the manual was. Although I had nothing to do with installation, the installation instructions helped me to understand where everything was located. For example, This kiln has an “ignition ring” for a pilot light. It is a metal pipe in a circle located under the kiln and on the inside of the burners. But for the manual I would have assumed it was just a support structure. The pipe has a hundred small holes in the top. With the gas to the pilot light on, lighting one section of the pipe quickly ignites the whole ring providing a pilot light by all burners. Cool!

Since this kiln has never been lit, we decided to light it empty just to make sure everything is running well. With the lid wide open and all doors and windows in the building open for ventalation, we gave it a try....

I turned on the main gas lever then turned on the gas to the pilot light and pressed the pilot light button. I could hear gas going to the pilot light ring and lit it with a long fireplace match.

The pilot light ring lit, but it did require lighting in a few different places to get the whole ring burning. Once lit, however, it stayed lit with no problem.

I then slowly turned on the main burners. One of the four burners lit. The others did not although we could tell they were getting gas. I shut off the gas to the burners and we adjusted the butterflies to almost closed. That helped. Two burners lit and a third tried. With some more adjustment, we had a third burner sputtering. We then just lit the two remaining burners with a match.

With the gas on high to see what it could do, we let it run for 15 minutes. Good heat, but I had two concerns:

1. The two burners we lit with a match each went out a couple of times and had to be relit. The pilot light should be doing this. I am afraid it is too far away on that side. (The ring is a bit skewed to one side, closer to the burners on the right.) However, since I had the gas so high so early, I am not too concerned (yet).

2. How do I put the lid down on this thing? The lid is not spring loaded, so it is heavy. There is only one handle - front & center, so closing it requires reaching over the lit kiln. I have raku tongs I can use, but that seems like bad planning. I will search the manual for answers before the real firing next week.

More next week....
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Day 2

Because of the problems keeping the burners lit, we tried one more test light before the real firing next Tuesday. Once the burners were lit with a match, the same problem arose. Two of the burners seemed to have problems staying lit. The flame was loud, fluttery and very orange.

I closed the butterflies all the way and then reopened them one full turn. In addition, I turned down the gas until the flame quit sputtering. The result was lovely blue flame with no flapping/sputtering sounds. I then closed the lid. The kiln reached 700 degrees in about 15 minutes. (Of course, the kiln was empty. It will take longer when full.)

I was very happy with this result. The burners had no problem staying lit and were heating well. Huge relief! It is interesting how similar this newly manufactured, small, top loading, updraft kiln is to the huge, handbuilt, old downdraft kiln I used to fire. (See "How to Fire that Big Old Downdraft Gas Kiln") It looks completely different, but the technology really isn't any different.

More next week....
 
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First Firing

Cool calm day.
Kiln lid open, peeps out, all windows and doors open.

8:10 light kiln. Back right burner won’t light.
Gas off. Check for blockage. None.

8:20 2nd light. The burners light. Very loud “whirring” noise from a burner. Adjust flames with butterflies. Flame is still very flappy and loud. Let it warm a bit.

8:50 The one burner the looks perfectly lit is cool and the paint is fine. The other three are hot and the paint is pealing from the outside of the air mix pipe above the burner. Looking at the flame, the good one is as wide as the pipe and has the bright blue color inside the column of flame. The others are thinner than the pipe and clear inside the blue column of flame. Straw inserted into the pipe through the butterfly space ignites. We obviously have flame in the air mix pipe. Review manual and follow instructions as follows:

9:00 Gas off. Lid open (never light a kiln with the lid closed), open butterflies slightly, relight with higher gas pressure. Perfect. Flame looks right, but still loud.

10:00 560°

QUICK NOTE: The target temperatures from the manual:
200° per hour to 600°
250° per hour to 1100°
I added light redux from cone08 based on redux recommendation from Tom Coleman
300° per hour to completion
I added 108° per hour the last two hours to give the glaze a bit of time.

11:00 730° Increase is not as high as I expected. Gas up a tick.

11:30 840°

12:30 990°

1:30 1090°

2:00 1125°

Okay, 400° in 3 hours is not acceptable. Gas Up a tick.

2:30 1200° Gas Up a tick again.

3:00 1325° Gas Up again so that the gas is a bit over 1/2 on. The kiln’s sound improved greatly. Just a wind sound, no “whirrrrrr” except occasional flicker of the sound.

3:25 1450° Gas Up a tick.

4:00 1590° temp increasing at 225 per hour, better but still under the 300 per hour target. Gas up again.

4:30 1675° Gas up again.

5:00 Okay, yes we are idiots.
As cone 08 was approaching, I tried to put the kiln into a light reduction by sliding a kiln shelf over the top vent. No flame at all from the peeps or top vent. Although I did not cover the top vent more than three fourths, I think I could have covered it all the way without any flame from the peeps or the top.

So, I scoured the manual for answers and found: “After the first hour, the gas should be slowly increased until it is on full.” We have barely been past half way at most today.

After banging my head against the wall a few times, I slowly increased the gas until it was on full.

5:30 1800° gas is now on full.

6:30 2025° - but I know my pyrometer does not function correctly after 2000°.

From here I will track by the color in the kiln until cone 9 falls. I do not believe we can finish at a reasonable hour tonight because of the delay. If the kiln color is not fully yellow by 9:30, I will turn off the kiln and try again next week.

LESSONS LEARNED TODAY:

1. Experience firing kilns has helped me learn that we use all our senses when firing. EYES: color of the flame to adjust the flame; length and color of flame from ports to adjust reduction atmosphere; or the color of the kiln to know temperature. NOSE: adjusting atmosphere by smell of gas; troubleshooting a stall in temperature by checking for reduction. EARS: adjusting the flame with the correct gas/oxygen mix; adjusting the pressure in the kiln. I can now add TOUCH: checking the burners for heat to see if the flame has backed into the air mix pipe.

2. This kiln has problems with the flame backing into the mix pipe. This is a problem I have never known before, but it is easy to see in the size and color of the flame once you know what you are looking for. Flame should be as wide as the pipe at the base, nice bright blue color with some blue flame inside the column of blue flame.

3. After the first hour, the gas should be on all the way. I have never fired a kiln that way because many kilns would go into heavy reduction and stall if the gas is on that high. But the flame sounded right with the gas on full. Sound of wind with a hiss of the gas. No loud flapping or whirring. I find this very interesting, since the problem we had in the test starts was the gas on too high. Obviously, this kiln is a bit finicky about the first hour of firing, but thereafter is designed to just run at top speed until done. This has an advantage over kilns that require constant adjustment because it eliminates a number of variables that can affect glazes. Unlike other kilns I have fired, I only adjust the reduction. If redux is consistant, the glazes should be too.

Updates later....
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First Firing - Conclusion

The first firing failed. We were able to reach about 2000 degrees, but it was simply too late at night to finish. At 11:00 pm, I turned off the kiln because the custodial staff wanted to go home. Will re-fire.

Second Firing:

Armed with the lessons learned in the first fire, we started the kiln at 7:30 am. After a slow heat for 1 hour, the gas was increased to full. Temperatures increased correctly thoughout the morning, reaching cone 06 at 11:30am - 6 hours earlier than the first fire.

However, at about 1950 degrees we appeared to stall. Since I have an analogue pyrometer, this is normally the maximum temp and I assumed there was a pyrometer failure.

Yet again, at 11:00 cone 9 had not started to bend. The color of the kiln was still bright orange. We have a serious problem. Kiln was turned off at 11:00.

After cooling, the kiln was unloaded. Although seriously underfired, there were some wonderful surprizes. The Bright Green shiny glaze (recipe in the High Fire Glaze FOrum) was a light blue with a sandstone texture. Shino was white, but fine. And the crystal green glaze was a lovely fine yellow. About half the kiln will require re-fire, the other half was a very pleasant surprize.
 
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Third Fire

I have a working theory that the second fire did not work because we did not have enough O2 after 2000 degrees. In the Art of Firing, Nils Lou writes that where the burner's air supply is too restricted, the air stratifies and stagnates. Air is needed to stir things up. Even reduction cannot work without proper movement. So, gas to max at the start, then butterflies open a bit to add some air. I also plan to make sure we are not over-reducing, causing a stall, with too much gas at the end. Okay, I have a plan.

I also have a new digital pyrometer from axner.com. It measure in F until 2000 then only in C. The conversion is C X 1.8 + 32 = F.

8:00 on - smooth! No flapping, perfect.
9:00 gas to 2/3
9:25 gas to max. Some wind sound, bit mild. No flapping.
10:10 dull orange color (1425 F)
12:00 Cone 06 at half on top (1700 F)
12:20 body redux
12:50 out of redux (1850 F)
NOTE: opening the top port to end reduction immediately dropped the teperature by 10 degrees.
2:30 1875 degrees - Yikes! The stall happened earlier than planned. Butterflies open 1/4 spin. Windy, no flame at top. Damper closed 1/3 - still no flame.
2:50 (1887 F)
3:40 (1966 F) Bright orange. Breathy, occasional flame from top vent.
NOTE: change over to Celsius
4:45 (1100 C = 2012 F)
5:40 (1129 C = 2064 F)
6:40 (1162 C = 2123 F)
7:40 (1186 C = 2166 F)
8:45 (1200 C = 2192 F)
9:00 Cone 9 well bent on top - how did that happen? We are at 2197 F which is too low for Cone 9 even at very slow temp increases. Of course, always trust the cone! My pyrometer is obviously off.
9:50 Cone 10 starting.
10:10 - unfortunatly, we need to turn off. I would have liked to soak in cone 10 for a while, but this will do.

20 hour cool.

The next evening, I opened the kiln and it was still too hot to touch, but there was no singing (the pinging sound caused when hot glaze cracks from sudden exposure to cool air) so we are cool enough.

Colors are nice. The only problem is a pinholing in a think walled shino pot. I suspect the very rapid temp increase at the begining of the fire. The organics did not have time to leave this thick walled pottery.
boundingfrog

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Reply with quote  #2 
I am looking at purchasing a used torchbearer of this type. They sound problematic. I need a small gas kiln that I can install into a residential area to do cone 10 reduction. They appear to be the only solution. Do you recommend them? What do you suggest?
MamereClaire

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Reply with quote  #3 

I have an Olympic updraft gas kiln.  The big problem I am having is it fires very unevenly.  The top shelf will not bend a cone 4, the middle shelf goes to cone 6 ( that is the cone I am firing to) and the two lower shelves go past cone 8. Anyone have an idea what I can do

Dawn

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Reply with quote  #4 
As you can see from my blog, these kilns are not "easy" to fire - but no gas kiln is easy.  Remember this is part of our art and will take just as much practice and trial and error to learn as throwing your first vase.

Over the course of a year, I did get the Olympic to fire predictably.  Take lots of notes so you can repeat the process when it works. 

The third firing (outlined in the blog) finally got some heat on the upper shelfs and, in fact, the cones droped on top first.  I attribute this to using a damper, so the first thing I think you should try is placing a kiln shelf on the lid of your kiln while firing.  (an old broken shelf works perfectly, but a small shelf will work) Use it as a damper to block the updraft hole by 10-25% once your kiln gets past 1200 degrees.  You can then just push it in to about 40% closed for the body reduction at cone 06.  You dont want to throw your kiln into a stall from reduction, just make that heat work a bit before rushing out the top of the kiln. 

Basically:  after 1200 degrees:  butterflies on the burners open to let lots of air in the bottom and kiln shelf blocking 10-25% of the top hole to keep the heat in longer.

When the cones 2 steps lower than your goal start to fall in any part of the kiln (ie: cone 8 if firing to cone 10) start working to even out the temps.  Damper in to 30-40% covered.  Again, make sure it is not so much that you temperature starts to fall from reduction, but slow down the rate of the temperature climb.  The manual recommends 300 degrees an hour from 1100 to completion.  I think that is impossible after 2000 degrees and not recommended even if you can get the kiln to do it.  60 degrees an hour is fast at cone 8,9,10 temps.  Too fast a climb at the bottom and the glazes at the top just dont have enough heat.

Another suggestion is in the loading.  Put large tall pieces in the center of the top shelf so that they force the air moving out the hole to work a bit on those upper pieces before it can get out. 

WARNING:  If using the shelf damper idea, do not place a platter or bowl below the hole.  A piece of something might be pushed into the hole when moving the damper and flaw the glaze.  This is rare because of the upward air pressure, but it can happen.  Vertical walled pieces are best right under the hole.

Give it a try.  I hope you will let us know if it works.  If it doesnt, let us know that too and we will try other suggestions.  Good luck,

Dawn Atkin   

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MarksPottery

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Reply with quote  #5 
Good post for me to see how the process goes. I know this was an older posts, how are things these days with your gas fired kiln?

I just agreed today to purchase a used gas kiln. I will have some work to do to get it ready to fire. Set up at home outside then build a cover, change from natural gas to LPG, get some kiln shelves and posts.

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kyongpottery

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Reply with quote  #6 
Dear members

I have given a small gas kiln size of 50 by 50 cm, two burner dawn draft kiln.

I try to fire cone 10 which I failed twice to reach it.

As temperature reach to high gas pressure gage rise up itself and drops temperature or hold on, so I have tried pressure down to rise temperature
it eventually rise in slow rate.

But then temperature stops moving around 1120-1140c for hours then I will put up gas then temperature drops.

I have a great difficulty to handle at the moment.

Is anyone could give me good advice for this firing?

Kyong
ClayArtsUtah

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Reply with quote  #7 
Quote:
As temperature reach to high gas pressure gage rise up itself and drops temperature or hold on, so I have tried pressure down to rise temperature
it eventually rise in slow rate.
 


Sounds like you are getting high reduction causing the kiln to stall.  You have fixed it by turning down the gas but then you dont have enough gas to get to higher temps.  Try adding more oxygen instead of less gas.  On my kiln that means opening the flue and the butterflies on the burners.

Dont give up!
kyongpottery

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Reply with quote  #8 

Thank you ClayArtsUtah

I am firing again today with new gas burners in same kiln and it still having great difficulty to rise temperature.
All most stopped at 1050c in 35kpa, I have opened damper fully and primer air as well but temperature is still not rising.
I am trying to neutralize firing to rise temps but I cannot get that stage with this kiln.
The flames coming out from the chimney too much!!!!!  Please help~

kyongpottery

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Reply with quote  #9 
Dear Members who might be interested

I have solved problem and fired again yesterday.
It worked beautifuly, it was so easy to fire after all.

What I had a problem is not enough oxygen for firing so I made the burner kiln floor holes bigger, from 40mm to 70mm, about double size bigger to give room to get oxygen in the kiln.

THANK YOU AGAIN FOR THE ADVICE!!!

Cheers

Dawn

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Reply with quote  #10 

I am so glad you solved the problem.  It seemed like O2 was the issue, but it is so hard to diagnose via internet.  Every kiln has its own little quirks.  Happy firing!


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Wendy

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Reply with quote  #11 
I am just starting to set up my new updraft Torchbearer kiln and am having trouble getting it to light.
The pilot circle lights OK and I can release the button and it stays alight, but when I turn the red main burner valve nothing happens. I don't hear any gas going to the main burners.
With nothing lit and the pilot feed turned off, if I turn the red main burner valve and press the green button, shouldn't I be able to hear the gas going through ?
JaxonV

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Reply with quote  #12 
I am considering purchasing a2831 torchbearer kiln and this blog has been VERY helpful. I currently am using a kiln I made myself . I have had very few really good firings, most of which I have had to refire in our Skutt then they usually come out fine. Its good to know that maybe its not the kilns fault, but the way I am firing it. I learn something new every time we fire this thing, and its not the first kiln I have built. So I have came to the peaceful conclusion that I need to use the above information and what I have learned and try to fire this thing properly instead of spending the bucks on a new kiln, yet. thanks 
ecumenik

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Reply with quote  #13 
I'm firing a 70yr old "Dickinson" kiln with a built in saggar box made of kiln shelf material. It has a 9burner circular array which I had converted from natural gas to propane. I'm running two 100lb propane tanks through a "high"-pressure regulator. The kiln has a 6X9" vent at the top.
I cannot cover the vent even partially without forcing flame to fan out at the bottom.
I've gone 9hrs and it doesn't look like cone5 has dropped. I finally got a solid "rushing" sound from the burners now that I've given up on reduction.
I believe the kiln was designed to fire porcelain glaze. It is made with hard brick and the box is the same material.
Any suggestions or helpful hints?
Thanks

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