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temp for opening kiln?


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Well I basically killed a new pair of wielders gloves. Most of the pots dunted and the ones that did not shivered. Glaze came off and pots tore themselves apart literally . The shelves mostly made it as did the arch (catenarys are tough )I recall losing one shelve.The pots on the rear wall also died.Although thats where the few keeper where. I think in the whole load I had just a few keepers. I learned that there are reasons for slow cooling -glaze development-clay bodies are happier -furniture lasts longer and does the kiln.

It was a school of hard knocks learning lesson-before that I was known as the (cooler king) in terms of kiln cooling. Now its  slow cool for me.

I have a sculpture in the yard that is a refrigerator form made of smxall extruder bricks so it look like a kiln-the label on the door says quick cool-I made it in art school some time later after my junior collage/home kiln quick cooling experiment went astray .

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On 1/14/2019 at 12:22 PM, Skye79 said:

I somewhat new to using my kiln, only having it a year.  I open it still hot, too hot to touch actually and have never had a problem. I didn't know that crazing was a possibility until reading this forum.  I do have a question about how to hold your temperature in a kiln sitter manual electric kiln... I use the plug on the top when I think it is at a good temp. to hold but I am completely guessing....no problems with it, I just don't know if it is making much difference. 

Well lift the latch back up to vertical position put a weight on latch rod to hold in place. Press the button on sitterbox to turn kiln back on.

Then fiddle the amount of energy input to jeep your kiln at soak temp. You can fire down in this way too. Take notes of what happens to temp.

Set yourself a timer or alarm as if you walk away, your kiln will remain jammed on.

Notes are a great help for future firing.

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  • 1 year later...
6 minutes ago, Juliagoolia said:

I wonder how many people reread this thread while standing next to their kiln, trying to justify opening it (or convincing themselves to keep it closed). I'm at 201. I'm opening.

I almost always cheat and crack it at 350-400, any crazing or defects that happen past that point will be evident during normal use anyway.

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While it's true that you can safely remove casseroles from your oven at >400F degrees, I was taught there is a difference when removing a piece from a hot kiln. 

When the pot is first created, the body/glaze are on their way down from several thousand degrees of heat and lots of things are going on in the body/glaze as the piece cools down; even at 400 F degrees.  Not the same as putting a finished piece in your oven, heating it up to a cooking temp and then removing it.   But with many variables in clay bodies, glazes and firing temps, who knows?  I always wait until I can handle the pots without wearing  gloves. 

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1 hour ago, nairda said:

While it's true that you can safely remove casseroles from your oven at >400F degrees, I was taught there is a difference when removing a piece from a hot kiln. 

When the pot is first created, the body/glaze are on their way down from several thousand degrees of heat and lots of things are going on in the body/glaze as the piece cools down; even at 400 F degrees.  Not the same as putting a finished piece in your oven, heating it up to a cooking temp and then removing it.   But with many variables in clay bodies, glazes and firing temps, who knows?  I always wait until I can handle the pots without wearing  gloves. 

Only thing I can think of where this would make sense is in glass annealing but even then the final 700 degrees can usually be cooled within an hour, so I don't know really.  Could be an interesting experiment for a student to do

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  • 11 months later...

Sorry for reviving an older subject, but I read through & couldn't resist adding a bit of devilry to the conversation.

A bit of background- I was (& still am) involved in the cast iron sculpture community long before getting into kilnwork, so a lot of my attitudes & approaches towards heat come from that side over 2500*F; we mostly work w/ propane starters to ignite coke fueled blast furnaces to hold ~3000*F for 5-12 hour long performance events. All of this lends to a "mas fuego" sort of candor regarding handling & being around extreme heat.

Anywho, I've done work at an outfit where toploading electric kilns were cracked 1" at 1000*F, with additional 1" cracks for every 100*F down to 5" at 500*, at which point it was considered "safe" to dive in & start pulling out lowfire tiles on advancer furniture. I think this was made SOP to make the fastest possible turnarounds. In a pinch, I found that we could, at an absolute SHTF maximum, pop lids fully open & dive in at 750. As long as we stayed below that 750* mark, we never really had any problems with glazes, ware breaking, or sudden furniture death. In any case, all of these kilns were also further crash cooled w/ batteries of electric fans aimed at their propped lids, & pulled ware was also cooled down in front of large drum fans.

Edited by bayanMM
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Crash cooling is hard on the kiln furniture. I have used a fan or two long ago to cool a kiln down-that said its best practice not to do any fast cooling.Best on the kiln,the furniture and the wares and on you. Yes you can do it but why?

I once took the door down after turning off a cone 10 kiln-most of the wares shivered. You learn the limits which is good but there really needs to be a reason after learning them to push them again.

Edited by Mark C.
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Patience is a virtue. I wait until room temperature. I taught ceramics at the high school for 20 years. I learned the hard way not give in to the students that were dying to open the kiln as soon as possible.  If we unloaded too early there were often very hairline crackles in the glaze that might did not show up until much later. I am sure if depends on your glaze. In my home studio I wait for room temperature even if I have a deadline.

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On 5/13/2021 at 9:50 AM, bayanMM said:

Anywho, I've done work at an outfit where toploading electric kilns were cracked 1" at 1000*F, with additional 1" cracks for every 100*F down to 5" at 500*, at which point it was considered "safe" to dive in & start pulling out lowfire tiles on advancer furniture. I think this was made SOP to make the fastest possible turnarounds. In a pinch, I found that we could, at an absolute SHTF maximum, pop lids fully open & dive in at 750. As long as we stayed below that 750* mark, we never really had any problems with glazes, ware breaking, or sudden furniture death. In any case, all of these kilns were also further crash cooled w/ batteries of electric fans aimed at their propped lids, & pulled ware was also cooled down in front of large drum fans.

Crazy! With all things in ceramics, there are exceptions to the rules, and ways to push the limits successfully. I think what made your situation possible was that they were a low-fire, porous tile. Just like raku pots surviving. I think if you were to try it with vitrified porcelain tiles you would have a different result. I also agree with Mark that crash cooling is hard on the kilns and furniture and using that way will shorten their lifespan. Clearly, your employer has found that the profit margins make it worthwhile, though. No judgement, the kiln is just a tool.

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On 5/13/2021 at 9:50 AM, bayanMM said:

Anywho, I've done work at an outfit where toploading electric kilns were cracked 1" at 1000*F, with additional 1" cracks for every 100*F down to 5" at 500*, at which point it was considered "safe" to dive in &

Too much risk for the average potter. Anything can be done on certain materials but why risk it. For me, 350 max, prop lid one inch, 200 unload (if I am desperate) but not on concrete or metal  so the bottom of the ware gets the heat sucked out of it and cracko! A nice wooden area is fine. But that’s as fast as I would push it. Too much work to potentially ruin as well as the wear on everything.

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