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Kiln firing a cone hotter? Please help!

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Hi! I am quite new to kiln firing. It's my first kiln,brand new and still has the original elements. Recently I've been noticing some issues with the fires. Most times it
seems that the kiln gets too hot as I use red clay that has the max temp of 1220°C and I fire to 1205°C and it still often shows signs of bloating on the higher levels in the kiln. I bought pyrometric cones to check. Cone 4(1181°C) cone 5(1205°C) and cone 6(1241°C).
I put cones on four levels of the kiln, (two of them exploded because I didn't dry the clay stand properly before; two on the lower level survived)
I have a kittec CB 120 s esp kiln.
The firing schedule:

60°C/h -> 100°C,

15 min hold,


Skip -> 1205°C

30 minutes soak

Free cooling
Cone results are in photos. Cone 6 also melted. Any suggestions, what am I doing wrong? Is the soak too long? I've got no clue.
Please help:)


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Well, first idea would be your soak, or any ending soak actually adds heat work making this unpredictable. When using cones and for predicting when fluxed reactions melt the last 100c is where most of the action takes place. Prior to that not all that much heatwork is accumulated. How fast you fire during this last 100c is important to predictability as well. So if using Orton cones to drop cone 5, I would pick 1186C target temp and begin my final segment at 1086 at 60 deg/hr until 1186. All your numbers are a bit above that and include a hold at peak.

Cones are made of glaze so they are a good representation of actual heatwork. How long something has been heating ( or what speed) in the last 100C for clay is an important part of the energy calculation.

The center column (60 deg/hr) is a nice compromise between speed and even kiln heating so I would use it most often for the final segment. 150 C tends to be less even because of speed and many kilns simply do not have enough power to maintain by the end of firing, even if set to go that speed, they often cannot keep up with this rate at peak temperature and produce random results.

Incidentally with holds or soaks at peak temperature, firing cone 5 with a fifteen to twenty minute hold to many potter result in firing to cone 6. You wouldn’t ordinarily bake something perfectly and add 30 minutes at top temperature without expecting to over bake it. Follow the instructions on you cone packs to get as accurate a result as practical.



Edited by Bill Kielb
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Hi Delis,

Welcome to the Forum!

Looks like you're well over cone 6 there.

Half an hour of soak at peak, that would add a lot of heat work!
If you're thinking a soak is required*, try "drop and soak" - where you drop 100°F (~56°C) then hold.

How long your kiln takes to reach peak temperature - the last 100°C or so - that's key, as Bill points out.
If the kiln is struggling to reach peak, you'll adjust the target/final temperature down...
If the kiln can reach peak temp easily and quickly, likely you're governing that final rate via the last ramp's programmed rate.

*Drop-and-Soak Firing (digitalfire.com)
I'm doing this...

Edited by Hulk
less imprecision, conversion error
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Oh dang, definitely hitting past cone 6. Not the worst problem to have. As stated above, in other terms, skip the soak. If that doesn’t do it, drop the peak temperature. Buying cones was the best gift you could give yourself. 

I’m a fan of “cone fire” programs, though I distrusted the technology for a couple years. If your kiln has that capability I suggest trying it. You simply put in/enter the cone you’re firing to. The programming is more sophisticated than I gave it credit for. The vast majority of kiln controllers are made by one company, for the most part the programming “just works.” 

This is a blip. You are in for a wonderful journey. Congratulations on your new kiln. 

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+1 for that being a hot cone 6, possibly a cone 7 where the second cone pack was. 

Others have addressed the heat and speed thing, I just wanted to add that if you make your cone packs out of fresh clay, it’s doable. Adding some sand or grog to the clay can help them dry without blowing, as will poking a bunch of holes in the clay log with something like a fork.  

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