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Kiln sitter cone completely straight after full fire?

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I was wondering if anyone could make a suggestion since last night I did a bisque fire at 04 cone. When I opened the kiln today the cone was completely straight, however it seemed the kiln did a full fire as I set the timer to 7 hours total and have never gone over that time span. I've used this method many times and have always gotten normal 90 degree bent cones so I was so taken back when the cone appeared as if no firing was done ? 

Could I of just gotten a defective cone ? I've used about 10 from the same pack with no issues. It's the strangest thing...

I've never used witness cones but now I feel I may need too.

Thanks for any advice! 


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If the timer shut it off, but the cone didn't bend, then the firing didn't get to temp. Either your elements are showing wear and the firing needs longer to complete, or something broke toward the end of the firing, like a switch died or a wiring connection fried out. After you unload the kiln, turn it on high for a bit and see ir all the elements glow. If they do, then it's probably that your elements are starting to wear and the firing need to go longer to reach temp. Ideally you'll want to get a multi-meter and check the resistance of the elements to see what condition they're in.

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I have seen a few rare similar situations where upon close inspection of the sitter, there was something impeding its movement. Check that the sensor bar moves freely, and that the bar itself is not worn or damaged. (I have also seen inadvertent mixups of the cones.  An 04 cone is brown both before and after firing, while a mid- or high-fire cone is a pastel color before firing and white afterwards. You probably didn't, but that's what I said the time I did it...) After checking everything, including elements, etc. as noted above by Neil, refire the load - and put some witness cones in so you know exactly what happened on the shelf; just because a sitter drops doesn't always equate to that cone in the middle of the shelf, and if the sitter doesn't drop because of a malfunction, it nonetheless may have reached the intended cone because of the timer. As for refiring the ware, it doesn't change the ceramic in any way if it reaches bisque temperature again, but in the off chance it was underfired before, this will bring it up to where you want it for consistent glazing.

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What size is your kiln? 

How soon did you turn the kiln to high?

7 hours for a  kiln smaller than 3cuft only half full may be ok. A kiln bigger kiln heavily loaded may be to short

On 5/14/2020 at 11:51 AM, Tia Sculpt said:

I've never used witness cones but now I feel I may need too.

Yes, by all means do.

Years back when I was still using a sitter kiln I've seen times when the ^04 sitter cone was straight and the ^04 witness cone was almost touching the shelf.

On 5/14/2020 at 12:38 PM, Tia Sculpt said:

Should I refire the current load

It can't hurt,  but lets say if the pots fired to the equivalent to ^06 you should be ok to just go ahead and glaze them.  Just remember that the pots will soak up fluid faster so if you are dipping your pots into glaze you may need to dip them for a shorter time. I don't brush so I can't speak to that.

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