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temp for opening kiln?

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Joy pots    20

Hi, I keep the kiln completely closed for the same time the firing took then I prop the lid. Usually wait again the same time of firing before unloading, but gradually pull the plugs out. Totally manual kiln with cones & a timer.

 

Happy firing

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Oh I love the phrase plug shuffle! What a variety of answers to this question...wonder what that proves, besides the obvious one that the impatience quotient varies among potters. Do those of you who open early get more crazing than if you'd waited?? Of course crazing is pretty, but isn't it bad on the inside of pots that will hold food?

 

I'm a new potter, 72 years young and after taking classes I've now had my own cellar studio for one year. I LOVE making pots! Electric kiln in the garage, and I agonize every time about this kind of question. How about the other end of the firing cycle—is it okay to close the lid and bung holes at the beginning and set it for a fast glaze firing?

And how about the bisque firing. If I'm sure the greenware is fully dry is it okay to do a fast firing, with everything closed??

 

Ginny Clark (Fort Wayne IN)

 

 

 

Hi Ginny,

 

I have an L & L with a computer. I always do a slow bisque and a slow glaze, I leave the top plug out and I do a 5 minute hold on the glaze. So far this works great.

 

I also make sure my greenware is real dry, I can tell by the weight when I pick it up. If I get in a hurry or I think its good and dry by its not, I have had some blow ups - not pretty!!

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Mudlark    3

i am also sometimes one of the impatient potters. i opened the kiln the other night at 11:30 pm so i would be able to sleep. it was at 220 degrees and i have gloves. the problem is that there is no room around the shelves to lift them off safely so i have to be careful to look only at the top shelf and guage the look of the rest of the load from what i put on the top shelf. didn't sleep well since i was able to see right away that all the pots i had done in one of the glazes was too thinly applied. (damn sprayer!, never me)

 

some of you have mentioned "dunting" without realizing that it is a condition caused by poor glaze fit, not firing. dunting can happen weeks after a firing and will startle you with the loud PING!!! i had this problem until i changed the clay body, the glaze recipe and the kiln. dunting is not a good thing. somewhere there is a crack in the pot even if you can't see it. a well made stoneware bowl will ring like a bell if tapped. if it goes clunk, it has a crack.

 

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Mudlark    3

Dunting is a firing/cooling fault and occurs at the cristobalite inversion temp of 226 deg C and at the siica inversion temp of 573 deg C, Dunting is not a glaze fault.It occurs in unglazed ware during both bisque and higher firings.It is one of the major problems to be considered when formulating flame proof bodies.

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Edith Marie    1

Because I work at another job during the daytime, I will look in at the top shelf, be amazed, then close the lid with all peeps still in and wait a day, so everything inside is compeltely cooled down. It is hard to wait but just like Christmas or Birthdays the wait is so worth it.....

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clayshapes    9

I'm part of the "can't wait for Christmas" crowd here. I tell myself I won't open the kiln until it's at 200 -- but I ALWAYS open it sooner. I crack the lid and peek in -- sometimes at 400(!!!!). Then I close it, scold myself and issue a stern warning to be patient...go have a coffee...and then come right back down and peek again. It's quite common for me to unload the top shelf at about 300 (wearing oven mitts, of course). I can sometimes summon the patience to not go further than that -- but not often.

I have been doing this for 2 years. I have NEVER had anything crack or break. I'm like the others who wonder -- If I can take something out of a 450 degree oven, why can't I take it out of the kiln?

I'm sure there is a logical answer to that question, and a finger wagger will be along shortly to explain!

Not that I recommend this. One of these days I'll learn my lesson -likely on a pot I can't recreate. Then I'll start meditating or something... or give up pottery all together...

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bciskepottery    925

The temperature read from the thermocouplar is heat in the atmosphere of the kiln; the actual wares and kiln shelves may be of a higher temperature as they will cool slower than the air inside the kiln. Just something to keep in mind, not wagging fingers. You seem to have a clay with good thermo-characteristics; on the other hand, I lost most of my work in a salt firing when the wares were removed too soon (the others in the group wanted to open early; I was the lone vote for the next day), with dunting starting as soon as the wares hit the cooler outside air. Obviously, not a good clay body for that situation. None of their work dunted.

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voceramics    2

After a couple of incidences with crazing and breakage with large flat pieces, we wait till the pieces are cool enough to hold in the hand to unload. Maybe a quick peek with the envirovent turned off below 300 F, otherwise we wait till below 200 F before turning off the envirovent and pulling a peep.

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I recently read (in Fraser, I think) that the issue is not so much temperature change as temperature differential on the two sides of the pot. If the pottery in your kiln is still hot, opening the kiln rapidly cools part, but not all, of the pot. Any weakness in the pot, even throwing lines, can crack. I once had a large bowl dunt, and it did so right along the throwing line.

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Bette    1

On occasions when I've had the dreaded pinging and crazing - not often, and not recently - I don't know whether it had anything to do with temperature shock. I now regularly bisque fire slowly and I have learned more about which of my clays/glazes fit together without crazing, and I suspect that has led to better outcomes rather than temp. Still, I now also wait to unload til max 150F to be safe.

 

If concerned about crazing and cracking, the hugely variable experience reported here is a great reminder that more variables are at work than just the unloading temperature!

 

As for unloading temperature as a cause of bad outcomes, it would be great to know the science, at what cooling temp point does your specific clay or your glaze no longer contract. I am new at this; maybe others have this knowledge? Personally, in the absence of knowledge, I test and expect to slowly learn the hard way. :/

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kdavitt    1

OK this may sound sillly but I would like to know at what temperature do most folks open their kiln??? My L&L says to wait until it is 250 F or below to open. So of course I open as soon as it hits 250 because one more second of waiting is just too much. But I get the feeling others wait for a much lower temp. So what is the consensus?

 

 

I remove plugs at around between 500 - 600. I take repeated peeks in the mid 400 deg. F range in electric kilns firing to cone 6 with stoneware. I crack the lid and keep it cracked around 300, open it all the way in the mid 200's and start taking ware out shortly after. I've had no problems.

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Mart    23

LOL smile.gif I am sitting here right now and witing it to drop below 100C 200C (200F) so I can crack the lid open and let it cool faster. I like to get the stuff out, glaze it and go home.

 

10 degrees C to go smile.gif

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My kiln shuts itself off usually late afternoon early evening (4-6:00pm) and I don't open it until the morning. I have noticed that my bisque firings are warm to touch in the morning and my glazed firings are usually cool to touch even though I expected them to be hotter since they get up to a higher temperature. I am assuming it's due to the glaze being less absorbent of the temperature.

I dont have a temperature on my kiln and I rely completely on the cones. So I have to wait until the next morning because I don't want to take a chance.

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Jime    0

This is a really useful thread, as I'm sitting here waiting to peek in the kiln.

I have a pretty basic setup, so I don't have a way to measure the temperature inside the kiln. Does anyone have tricks for gauging the temperature inside?

When the kiln was pitch black inside I took out the second peep.

I've heard of people doing the paper test, but I'm not too sure what temperature is represented by which results. I just took some paper and left it in for 10 seconds, and got a tiiiiiny bit of color change, barely tan, not brown.

I have a small electric cress 23. Any idea what temp it might be if the top of the lid is warm? cool?

thanks!

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Hi all...

 

I have heard that opening the kiln between 200°F and 100°F is bad for the elements, causing them to wear out prematurely. Same for pulling the plugs or cracking the lid. Regardless if it's bisque or glaze.

I can't find any data to back that up. 

 

I can understand the care for porcelain, as that material would need careful cooling. but if one is quickly fetching out pieces, not leaving the lid open, I fail to see the harm in opening the lid versus the life of the elements.

In reading this thread, I see none has mentioned the elements even once. 

I can respect the concern (where I first heard it) they have about waiting to give the elements a good run for the money, but if its truly moot and has no impact on the elements, then it would be really nice to clear that up.

 

Any one know?

 

Thanks

RG

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You probably have a lot more pieces in a bisque firing to hold the heat in the kiln compared to the air in a glaze firing.

 

My kiln shuts itself off usually late afternoon early evening (4-6:00pm) and I don't open it until the morning. I have noticed that my bisque firings are warm to touch in the morning and my glazed firings are usually cool to touch even though I expected them to be hotter since they get up to a higher temperature. I am assuming it's due to the glaze being less absorbent of the temperature.
I dont have a temperature on my kiln and I rely completely on the cones. So I have to wait until the next morning because I don't want to take a chance.

 

I only open my kiln under 150degC after reading articles saying glazes are more about what happens after the kiln is turned off.

 

I usually forget how hot 150 is and burn my fingers on the pots. I think too relatively.

 

No idea about element life, I mean they go from room temps to very hot quite quickly so is it any worse the other way round?

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neilestrick    1,379

Hi all...

 

I have heard that opening the kiln between 200°F and 100°F is bad for the elements, causing them to wear out prematurely. Same for pulling the plugs or cracking the lid. Regardless if it's bisque or glaze.

 

I can't find any data to back that up. 

 

I can understand the care for porcelain, as that material would need careful cooling. but if one is quickly fetching out pieces, not leaving the lid open, I fail to see the harm in opening the lid versus the life of the elements.

 

In reading this thread, I see none has mentioned the elements even once. 

 

I can respect the concern (where I first heard it) they have about waiting to give the elements a good run for the money, but if its truly moot and has no impact on the elements, then it would be really nice to clear that up.

 

Any one know?

 

Thanks

RG

 

Nope, never heard that. If you waited for the kiln to get below 100F  before opening, it would take days. You've got to get the lid open at some point.

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kdavitt    1

For 4 years now I've been opening the lid of a glaze firing and looking in a number of times from 600F on down. Around 450 I prop the lid a couple of inches open and at 400 I open all the way. I remove the pots at around 220. I do about 2 full loads of 2 or 3 kilns 2 or 3 times weekly and I've had no problems. The attached (if it shows) was taken with the kiln around 430. By the way, that particular kiln has had about 250 firings with the same elements.

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perkolator    53

For crash cooling I usually let the students pull spy plugs below 600*.  Crack the lid with a piece of soft brick when it's below maybe 400*.  Fully open lids at 250* or lower and unload with gloves if need be.  Typically leave vent on until room temp.

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Marcia Selsor    1,301

I always used the paper test. fahrenheit 451 is the temperature at which paper burns. The movie by the same name written by Ray Bradbury is interesting if you get the chance.

I start cracking doors or lids at that temperature but wait til 250 or so to open completely.

Marcia

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I fire cone 5 with and electric kiln, leave all the plugs in and wait until the kiln is room temperature. i put too much time into my pieces to ruin the glaze just because of my impatience.  When I was teaching, the kids who procrastinated and did not get their work in on schedule where up against grade deadlines. I would warn them if I opened the kiln early they risked fine cracks in the glaze.  The times that I gave in and unloaded at 120 degrees almost ended with the "pings" of cracking glaze.

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Joseph F    865

I am with the 250F folks. Anything more and I feel like I am just wasting time. I open at 250F let it cool to room temp, then take the pots out. Takes about an hour or so after I open it. 

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