Jump to content


Photo
- - - - -

Newbie With Kiln Issues - Help, Please?

kiln overfiring

  • Please log in to reply
12 replies to this topic

#1 nijereel

nijereel

    Newbie

  • Members
  • Pip
  • 3 posts
  • LocationBrooklyn, NY

Posted 01 February 2014 - 12:17 PM

Hello community!

 
I recently set up my Olympic F2327HE kiln in my studio along with the Orton vent and fired my 1st bisque and glaze this past week.
 
I am a new kiln owner (have always relied on/used shared ceramic studio kilns) and need help figuring out the following issues I ran into in both firings:
 
Bisque firing
Set to: Fast bisque
Cone: 06 / 1828
Pyrocone: On all shelves/levels. Overfired
Notes: 
- The kiln was not 100% full. All 3 shelves had pieces on them, probably at 65 - 70% capacity.
 
Questions: 
- Does the quantity of wares inside the kiln affect the temperature inside the kiln? Does it matter if I have 2 wares or 20 wares?
 
Glaze firing
Set to: Fast glaze
Cone: 6 / 2232
Pyrocone: On all shelves/levels. Overfired
Notes: 
- The firing took longer than what the chart on manual states the firing time would be. Instead of 4-5 hrs, it ran for 7 hours and instead of stopping at 2232, it stopped at 2240.
- The firing logged and firing #3 instead of #2 (this was my second firing in the kiln, the 1st one, bisque above, logged #1 correctly)
 
Questions:
- Why did the kiln fire longer than normal? (and above the temperature?)
- Kiln logged the firing as the 3rd time, though it was only my 2nd run - how come?
- Regarding smells: Assuming the vent is properly installed (which I believe it is!) am I to expect absolutely no smell at all? Noticed on both firings there was a noticeable burning off smell. 
 
----------
 
Any help/advice/tips would be much appreciated!!
I've contacted Olympic and have not received any replies yet..
 
Thank you.
Kind regards,
Nijer E.


#2 Chris Campbell

Chris Campbell

    clay stained since 1988

  • Members
  • PipPipPip
  • 2,299 posts
  • LocationRaleigh, NC

Posted 01 February 2014 - 07:33 PM

NIjer ...

First comment is that bisque firings should be medium to slow for best results ... Same with glaze firings.
Why are you doing fast fire on them?

Second ... Are you using witness cones inside? That is how you can see exactly what is happening on each level. You mention they are over fired but you don't tell us how you know that. The end temp of the kiln is not how you accurately determine what Cone it fired to. Sorry, I have no idea what a pyrocone is??

The factory might have tested it once, thus the higher number.

Even with the exhaust system you are going to notice smells from off gassing.

My advice would be to buy some witness cones ... These are a group of three cones ... For a cone 6 firing you would place a 5,6,7 on each level to determine how your kiln is firing. Then take notes on each time you fire. How much work was in the kiln, how long it took, how even it was etc. That is the best way to get to know your kiln.

Chris Campbell
Contemporary Fine Colored Porcelain
http://www.ccpottery.com/

https://www.facebook...88317932?ref=hl

TRY ...   FAIL ...  LEARN ...  REPEAT


#3 Evelyne Schoenmann

Evelyne Schoenmann

    Ceramic Artist

  • Members
  • PipPipPip
  • 236 posts
  • LocationSwitzerland and Italy

Posted 02 February 2014 - 06:30 AM

Hello Nijer and welcome to the forum

 

As Chris already asked: why are you firing so fast? I don't have an Olympic but a Nabertherm, but I think it's the same with every type of kiln, so my firing schedule for a bisque is: in 7 hours to cone 019 and another 4 hours to cone 06. So a bisque takes 11 hours for me. A glaze firing (normal glaze, nothing special, no ash glaze) as follows: in 6 hours to cone 019 and another 5 hours to cone 6, so also here at least 11 hours of firing. Sometimes I let the kiln heat still more slowly.

Is there a reason you want to bisque or glaze fire in only 4-5 hours? What do mean with the kiln was overfired? How was the ware looking when you opened the kiln? Did you take pictures to show us?

For all the technical questions about your particular kiln you have to wait for Olympic to answer you.

A word about the # of firings: my kiln came already tested by the supplier and that was firing #1, but in my case he told me.

Another question: the first firing for YOU should have been the kiln-wash-on-shelve-firing, without pieces on the shelves. Did you do that already? If not, I would highly recommend putting the kiln wash on the shelves and fire them before the next glace firing

I've found a website with informations about your kiln:

 

http://www.clay-king..._2327_kiln.html

 

Keep us informed and if possible post pictures of the wares that was in the kiln you are not satisfied with.

 

And please fill in the member section on this forum (your profile). It would be less impersonal. We are among friends here. Thank you.

 

Evelyne


Evelyne Schoenmann
Studio: schoenmann ceramics
In love with alternative firing methods
www.schoenmann-ceramics.ch


#4 nijereel

nijereel

    Newbie

  • Members
  • Pip
  • 3 posts
  • LocationBrooklyn, NY

Posted 02 February 2014 - 12:11 PM

Hi Chris, Hi Evelyne, thank you for the quick replies!

 

I did the fast firing because it was a 'test' fire. I used a witness cone 06 for the bisque and witness cone 6 for the glaze firing. I'm aware I should've used a cone up and under for each firing. I will on the next firing. The witness cone on both firings were completely bent, indicating over firing. I didn't notice any over firing (or anything wrong) with the pieces on bisque firing but the cone bent - however, with the glaze firing, the glaze results were definitely different from what I'm used to (when I used the shared kiln.) - so along with the cone bent completely, I'm assuming it over fired.

I didn't use a custom firing schedule, only the programmed ones on the Bartlett controller.

 

I did apply kiln wash on shelves on 1st firing (not empty though - it was the 1st bisque firing.)

 

I'm learning that perhaps, the programmed firings may not be accurate with the actual temperatures the kiln is firing?

My main concern is that the kiln continues running even after it's reached it's target temp (I'm assuming that's why it's over firing the pieces.)

 

Is it best to program your own firing schedules? Is there a 'base' reference/chart you recommend? I'm aware it's all about trial and error and I need to get to know my kiln better, but I'd be helpful to have a starting point.

 

I'll keep you posted.

 

Thank you for your help!

 

N.



#5 Chris Campbell

Chris Campbell

    clay stained since 1988

  • Members
  • PipPipPip
  • 2,299 posts
  • LocationRaleigh, NC

Posted 02 February 2014 - 12:53 PM

I am assuming this is a computerized kiln with a Bartlett controller?

If so, read your manual, then try medium speed, programmed firings with three witness cones on each shelf.
Try to assume your kiln is firing correctly until accurately proven otherwise.
Right now you are second guessing the Bartlett folks who ... along with the Orton crowd .... wrote the book on firing.

Fast firings are generally reserved for special cases and do not work well for bisque or glaze firings.

Chris Campbell
Contemporary Fine Colored Porcelain
http://www.ccpottery.com/

https://www.facebook...88317932?ref=hl

TRY ...   FAIL ...  LEARN ...  REPEAT


#6 Barb Muncie

Barb Muncie

    Newbie

  • Members
  • Pip
  • 2 posts

Posted 02 February 2014 - 09:14 PM

I went back through and reread your post a couple of times. If I'm reading this correctly, you fired at 06 with an 06 witness cone and at 6 with a 6 witness cone. It would be correct for them both to the bent over. If you fired these same temps with the 07 or 7 cones and they were bent over then there might be some reason to suspect they were firing too hot. All in all, it would appear that you are right on track.  :)



#7 Norm Stuart

Norm Stuart

    Advanced Member

  • Members
  • PipPipPip
  • 639 posts

Posted 02 February 2014 - 09:20 PM

I would definitely leave open the possibility that you will always choose the next lower cone-fire program using your Bartlett controller.

 

We discovered the cone-fire programs in our Bartlett V6-CF controller all fire uniformly one Witness Cone too much on all speeds and all cones chosen.  It merely cost us a half box of various witness cones when we first received our Cress E-23 kiln.  One cone too high on Cone 5, Cone 6, Cone 04, Cone 06, Cone 016, and Cone 022.  There's a nearly random number of degrees between all of these cones, yet it was always one cone too much whether we chose Slow, Medium or even Fast with the cone-fire.

 

As odd as this is, exactly one cone too much is a relatively easy quirk to adapt to. Simply choose the next lower cone-fire program.

 

I asked Steve Issacson at Bartlett Tech Support three years ago if they might have a "look-up indexing-error" in their program in the EPROM which might account for this.  Supposedly the engineers went through the program again and say there isn't.  If you have a non-customized version of the V6-CF controller, Bartlett already has a program update they can flash your EPROM with if you send back the controller board. It adds additional capabilities to the controller.  But this is not yet available for any of the controllers customized for each kiln maker with their name on the front.

 

If you find your variance is not uniformly one cone too hot, you can use the CnoS or TnoS options to individually adjust the target temperature.

 

Cress's answer for this quirk is that it is a potter's tradition to place Witness Cones next to the peephole which will always fire one cone lower than the rest of your kiln.  You've got to give them credit for quick thinking for that explanation.  It's so strange it might even be true.

 

Hi Chris, Hi Evelyne, thank you for the quick replies!

 

I did the fast firing because it was a 'test' fire. I used a witness cone 06 for the bisque and witness cone 6 for the glaze firing. I'm aware I should've used a cone up and under for each firing. I will on the next firing. The witness cone on both firings were completely bent, indicating over firing. I didn't notice any over firing (or anything wrong) with the pieces on bisque firing but the cone bent - however, with the glaze firing, the glaze results were definitely different from what I'm used to (when I used the shared kiln.) - so along with the cone bent completely, I'm assuming it over fired.

I didn't use a custom firing schedule, only the programmed ones on the Bartlett controller.

 

I did apply kiln wash on shelves on 1st firing (not empty though - it was the 1st bisque firing.)

 

I'm learning that perhaps, the programmed firings may not be accurate with the actual temperatures the kiln is firing?

My main concern is that the kiln continues running even after it's reached it's target temp (I'm assuming that's why it's over firing the pieces.)

 

Is it best to program your own firing schedules? Is there a 'base' reference/chart you recommend? I'm aware it's all about trial and error and I need to get to know my kiln better, but I'd be helpful to have a starting point.

 

I'll keep you posted.

 

Thank you for your help!

 

N.



#8 bciskepottery

bciskepottery

    Advanced Member

  • Members
  • PipPipPip
  • 1,558 posts
  • LocationNorthern Virginia

Posted 02 February 2014 - 10:09 PM

A couple things to think about . . .

The cones you use operate on heat work, not temperature. Also, the rate of temperature increase in the last one or two hours is most critical. If you look at an Orton cone chart, it will tell you that the faster the rate of temperature climb at the end of the cycle, the higher the end temperature might be before the cone falls; conversely, a slower rate of temperature climb, the cone falls at a lower temperature. And, the type of cone (self-supporting, large, small) also vary. For example, a self-supporting cone at Cone 6 will fall around 2165F if the rate of temperature increase is 97 degrees F, vs. 2232F if the final rate is 107 degrees vs. 2269F if the final rate of increase is 270.

Also affecting the look of you cone would be a hold at top temperature . . . which give more heat work.

If you think your kiln is firing hot, then you can also program in a thermocouple offset to account for that difference. There should be instructions in either the Bartlett manual or Olympic kiln manual on how to do that.

Regarding time for firings, my L&L manual shows times for a firing cycle based on an empty kiln, and notes that actual firing times may take longer depending on how much wares are being fired. So, consider the times in your manual as a guide, not gospel.

How much is in the kiln will affect your firing times, as will the thickness of items, etc.

#9 Chris Campbell

Chris Campbell

    clay stained since 1988

  • Members
  • PipPipPip
  • 2,299 posts
  • LocationRaleigh, NC

Posted 02 February 2014 - 10:50 PM

Sorry to be repetitive ...
But until you do firings with three witness cones on each shelf you do not know what is happening. One cone does not tell you much ... Only that the particular spot it was placed reached a certain temp. So reacting to two firings is not productive.

Factors like how close it was to pots and kiln furniture ... How full or empty the kiln was ... Was it near the elements or was it placed in the middle of a full shelf. This is what you learn from your witness cones each time you fire so move them around some.
You learn where your kiln fires hot or cool.

Sure, we like to think our electric kilns are predictable machines but they too have quirks .... Take notes to build your learning base from firing to firing. After a while, your experience will help you fire every load the way you want to. Experience and evidence is key. Like Norm says, it will only cost you a few boxes of witness cones.

Chris Campbell
Contemporary Fine Colored Porcelain
http://www.ccpottery.com/

https://www.facebook...88317932?ref=hl

TRY ...   FAIL ...  LEARN ...  REPEAT


#10 Arnold Howard

Arnold Howard

    Graduate, School of Life

  • Members
  • PipPipPip
  • 255 posts
  • LocationMesquite, Texas USA

Posted 04 February 2014 - 10:49 AM

When a controller consistently fires one cone too hot, the problem is likely the thermocouple rather than the controller. We have found that the controllers typically are accurate to within several degrees F. (We have a thermocouple calibrator at the factory that can test the accuracy of a controller.)

 

I agree that the easiest way to correct the inaccuracy is to program the controller for the next cooler cone.

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com

 



#11 Norm Stuart

Norm Stuart

    Advanced Member

  • Members
  • PipPipPip
  • 639 posts

Posted 04 February 2014 - 03:11 PM

Arnold - I'd agree a wonky thermocouple is the most likely suspect, which is why I hopefully retested after replacing our Type-K when we replaced the heating elements about 14 months later.  (We fire our kiln about 186 times a year - 12 months)

 

Last year I replaced the thermocouple with a Type-S, with related changes, and retested - if anything, even more exactly one cone too much work regardless of firing speed or cone-fire program chosen.  I'm more convinced there's a programming error, but it's still very easy to choose the next lower cone.

 

If and when Bartlett has an update available for the Cress customized version of their V6-CF, I'll get the EPROM flashed and run through some more Orton witness cones testing the kiln again.

 

If I had not personally experienced this, I'd never have believed it.

 

When a controller consistently fires one cone too hot, the problem is likely the thermocouple rather than the controller. We have found that the controllers typically are accurate to within several degrees F. (We have a thermocouple calibrator at the factory that can test the accuracy of a controller.)

 

I agree that the easiest way to correct the inaccuracy is to program the controller for the next cooler cone.

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com



#12 Arnold Howard

Arnold Howard

    Graduate, School of Life

  • Members
  • PipPipPip
  • 255 posts
  • LocationMesquite, Texas USA

Posted 04 February 2014 - 05:34 PM

Norm, that is interesting. Maybe your controller is one cone off. I like the simplicity of your solution, which is to program a firing for one cone cooler. I think you will like the S-type thermocouple.

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com



#13 nijereel

nijereel

    Newbie

  • Members
  • Pip
  • 3 posts
  • LocationBrooklyn, NY

Posted 07 February 2014 - 02:17 PM

Thank you everyone - I truly appreciate it!

I'm firing a bisque next week and will apply the tips I received here.

Will keep you posted.

 

N.







Also tagged with one or more of these keywords: kiln, overfiring

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users