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Middle Of Kiln Is Overfiring


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#21 Chilly

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Posted 19 April 2014 - 01:54 PM

I feel your pain.  I just unloaded a glaze firing.  The bottom shelf was cone 4 , middle two cone 5, and top cone 6.  I can handle cone 5 and 6, I have glazes that I like at each.  At cone 4 everything is under fired.  My kiln is digital but only has one probe, in the middle.  I'm hoping to stack things differently next firing and see if it will even out.  I don't know what else to do.

 

Does a longer soak at the top temperature help to even things out?


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#22 Min

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Posted 19 April 2014 - 03:59 PM

 

I feel your pain.  I just unloaded a glaze firing.  The bottom shelf was cone 4 , middle two cone 5, and top cone 6.  I can handle cone 5 and 6, I have glazes that I like at each.  At cone 4 everything is under fired.  My kiln is digital but only has one probe, in the middle.  I'm hoping to stack things differently next firing and see if it will even out.  I don't know what else to do.

 

Does a longer soak at the top temperature help to even things out?

 

 

Yes, but it also increases the final heat work amount. Longer the soak the cooler the temp you start at. My kiln, my schedule, my thermocouple, I soak at 2200 for 35 minutes to bring ^6 down to tip touching. All kilns are different, it's one of those things that you have to play with. 



#23 bciskepottery

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Posted 19 April 2014 - 04:30 PM

Slowing the rate of temperature climb for the last 200 degrees or so might allow the top and bottom to catch up and even out.

#24 clay lover

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Posted 20 April 2014 - 07:32 AM

I have a similar kiln. When I started putting taller shelf posts, at least 5",  for the bottom, therefore having more elements under there, the temp came up a full cone.

Have you checked that all elements and thermocouple are working?  My BRAND NEW kiln needed a new motherboard.  Nothing I did got it to fire correctly.  When the was replaced, all was pretty even. But bottom still too cool.

Another thought, what peep plugs do you have out?  I quit taking out the bottom 2 plugs and that also helped the temp there.  I keep the plug beside the thermocouple in, that seems logical to me.  

Do you use any 1/2 shelves?



#25 Chantay

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Posted 20 April 2014 - 12:45 PM

I just unloaded my kiln yesterday.  I took the advice previously posted here to place taller items in the bottom and tighter at the top.  It fixed the uneven firing I was having.  Witness cones on all three levels where the same.  I have a digital controller, fired to cone 5 with a med ramp and 15 minute hold.  Cone 5 was completely over with tip a little bent.  This is perfect for my clay and glazes.  Now the weird thing is I seem to be getting some reduction going on.  I like the way it looks but not sure at this point if it is repeatable or controllable.


- chantay

#26 JBaymore

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Posted 20 April 2014 - 01:15 PM

......... I seem to be getting some reduction going on. 

 

Why do you think that?

 

best,

 

......................john


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com




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