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Results Of First Kiln Firing There Seems To Be Some Temperature Variation

Cones bent unequally

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#1 Pugaboo

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Posted 07 July 2013 - 10:02 AM

I test fired the kiln for the first time yesterday, you can see this under another posting. I fired an Olympic 1823HE electric kiln with an orton downdraft vent.

I fired with all the peep holes plugged to ^06 on a fast glaze firing. it took 3:56 to complete the cycle. top heat measurement according to the digital read out was 1839. It cooled over night and when I opened it this morning to check the test cones inside they varied a lot from what I could see, please see attached photo.

Going from left to right in the photo:
Top most shelf placed about 4 inches down from lid, shelf was positioned just below the peep hole at this level. There was 1 row of elements between shelf and lid.
Cone 1 - directly in front of peep hole on edge of shelf
Cone 2 - placed in very center of top shelf

Middle shelf was placed 8 inches down from the top shelf just below the level of the 2nd peep hole. There were a couple rows of elements between shelves.
Cone 3 - directly in front of peep hole on edge of shelf
Cone 4 - placed in very center of shelf

Bottom shelf was placed 4 inches down from middle shelf just below the level of the 3rd peep hole. There was at least 1 row of elements between shelves.
Cone 5 - directly in front of peep hole on edge of shelf
Cone 6 - placed in very center of shelf

Just above the floor of the kiln I placed 1/2 inch posts with a whole shelf sitting on it. I plan to leave this in the kiln permanent so am calling it the floor shelf. I unfortunately did not place any test cones on this level and I probably should have thinking about it now. I followed the directions and placed them on each shelf with a peep hole but in future will also place cones on this level as well.

It looks to me like the kiln is cooler on the top and hotter on the bottom and from what I have read this is opposite of what normally happens. Meaning usually a kiln fires hotter on the top and cooler on the bottom. Though I did read somewhere else that the temperature in a kiln can vary as much as a cone cooler on the top shelf as compared to the bottom shelf. I can only go by what I have read as I have never fired a kiln before.

So do I have a problem? If so how how do I fix this? It's a brand new kiln and this was its very first test firing with only shelves, posts and cones inside of it.

Attached Files


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#2 Chris Campbell

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Posted 07 July 2013 - 11:04 AM

No, you don't have any more of a problem than any other electric kiln.
First off I never use the fast fire setting for a glaze load as that is exactly what happens ... a very uneven firing which will never produce a whole load that looks the same. I use medium speed with a 10 - 15 min. hold at the end, then a controlled cooling for nice even results. Others will have different timing according to their glazes and desired results. It just takes time and firings to learn this.
For witness cones try using three so you can see what happens ... For instance if you want Cone 6 have a 5,6 and 7 on each level. Then you know where to position your work within the kiln to get the results you want.
Also, you don't have to sit around watching your kiln the whole time. As long as you installed it according to the safety/electric standards you can leave it til the end of the firing.
Yes, you will smell stuff burning out ... That is natural and of course another reason not to sit there while it fires.
As to shelves and how to load ... I think there are videos available online ?? Seems I read about a 'How to Load Your Kiln' one. People who have nice predictable shapes in their work have all kinds of rules about loading but those of us who make weirdly shaped things have to adjust and scramble. My loads are very often a weird looking jumble but always have three posts under each half shelf.
Mostly though, have fun on your journey of learning to fire. It is fun and awful and crazy and fun again.

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#3 Diane Puckett

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Posted 07 July 2013 - 12:54 PM

I agree with Chris. If I ever open the kiln to sets of identical and perfect cones, and all my pots are flawless, I will know I have died and gone to heaven.

Re your question in your other post about the posts under your bottom shelf - It really bothered me that the posts under my bottom shelf were sitting on the kiln floor outside the area sitting on the kiln stand. Several people told me it was fine, but that made no sense to me, as it puts all the weight on the unsupported brick. I recently read an article, I think by Vince Pitelka, though I am not sure, where he said to put those bottom posts so that they rest on the brick which is sitting on the stand.
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#4 Benzine

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Posted 07 July 2013 - 01:55 PM

Chris, I've used the "Fast Glaze" mode on my L&L classroom kiln, and never run into any problems.  If I can avoid it, I'll do a standard firing, but sometimes, at the end of a term, I'm trying to get things fired and handed back, so the quick firing saves time.  Of course, I am onl firing to 04/ 05, so that could be the difference. 

 

In regards to setting up the posts, I've been told that every few months, to a year, you should rotate the shelves, to avoid putting repeted stress on the kiln floor.  So let's say you put your half shelves running "Up and Down" in relation to you.  After a few firings, your should set them, left to right.  Any truth or reason to this?


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#5 Mark C.

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Posted 07 July 2013 - 02:12 PM

In reguards to unsupported floors.I have always added more metal under the entire kiln on top of the stand and under the floor as it makes sense as far as supporting the load. This cures the unsupported stand that is a poor idea to start with.

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#6 clay lover

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Posted 07 July 2013 - 02:21 PM

Looks like a full cone difference from top to bottom, too much for me. How you stack and how you fire are more important than the vent, from my experience, in determining the evenness of the whole load.

Try to have AT LEAST 2 elements between shelves and use 1/2 shelves as much as you can. Have at least 2" below and 2" above the thermocouple open. more is better. I think your top shelf was too close to lid, if only 1 coil was there, I never go closer than 5" to the lid. I have a Skutt 1027, with one thermocouple and 6 peeps. No vent. I get no more that 1/2 cone difference through out, but much experimentation went into that. I remove the 2nd and 5th peep and fire a lot slower than you do.
Look in 'Mastering Cone 6 Glazes' for a good schedule for ^6. A soak of 20-30 minutes at peak can make a lot of difference in evenness.
Hang in there you have to learn your kiln.

#7 Chris Campbell

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Posted 07 July 2013 - 02:22 PM

Benzine ... does your L & L have the thicker walls? It could be that your firing range is lower, but if it works ... go for it!

 

Also, I set every second layer of shelves at right angles to the one below whenever I can. Meaning that the center space would make a cross if you could look straight down ...make sense? I started doing this after reading something, somewhere??

 

The insides of my kiln loads have looked like every possible choice through the years and you learn to adjust your schedule to the load ... thank goodness for computers!!!


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#8 timbo_heff

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Posted 15 July 2013 - 11:15 AM

Make sure your cones are not close to peep holes : that could expain the strange cone results too !



#9 Benzine

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Posted 15 July 2013 - 11:37 AM

Benzine ... does your L & L have the thicker walls? It could be that your firing range is lower, but if it works ... go for it!

 

Also, I set every second layer of shelves at right angles to the one below whenever I can. Meaning that the center space would make a cross if you could look straight down ...make sense? I started doing this after reading something, somewhere??

 

The insides of my kiln loads have looked like every possible choice through the years and you learn to adjust your schedule to the load ... thank goodness for computers!!!

Hmmm....I honestly couldn't say.  They really don't seem any thicker, than the Skutts I've used in the past.  The next time I'm in my classroom, I'll measure the thickness, and report back.

 

If it does turn out the walls are thicker, it would explain, why I've never had any glaze defects, from rapid cooling, in this kiln.  This is in contrast to a fair amount of blisters, from popped glaze bubbles, that didn't have a chance to smooth out, that I experienced in one of my computer controlled classroom Skutts.  I loved that kiln, but those bubbles were annoying.


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#10 Pres

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Posted 15 July 2013 - 07:04 PM

I usually havep a 1/2 cone of difference top to 1/3 from bottom. When firing alarge load opf patens with spirall stacking the same amount of deviation.

Temp differences can be handy. We had Sea Green Pearll from minnesota, or ART, was rated 5-6. More a 5,and even then ran like an ash. Told students to not put it lower than 3" from bottom, and I loaded into cold spot. Second year students loaded bisque and glaze under my watch, when I changed or did something different, it was an opportunity for explanation.

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#11 weeble

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Posted 21 July 2013 - 04:28 AM

With your downdraft, you've got holes drilled in the top and bottom.  SO, where were your holes in relation to the cones?  Back when I first installed one, I didn't even think about it and placed a piece almost directly under one of the vent holes.  There was a spot of un-fluxed glaze lined up perfectly with the vent hole, so that could be part of the problem with your top shelf seeming cooler.  Also, the Envirovent recommended (if I recall correctly) 1 inch spacers between the bottom shelf and the floor of the kiln for proper airflow.  You might want to double check the specs on yours!


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