[morah]

Hi everyone! I am a newbie to this site and to ceramics in general. I've been giving ceramics classes to kids this summer and there is a lot of pressure to get the projects done. I have an L&L e23s electric kiln and I've been firing to 06 and 04. What temperature is it safe to open the kiln at for bisque and what temperature for glaze? The projects are relatively small and thick. thanks

[Dinah]

Hi Morah,

Quick answer: 93d C. for bisque and gloss firing then you can open kiln and touch pots. If you have opened gloss kiln and things are pinging, and you need gloves to handle the ware...stop. Close. lid. and. wait. I will crack the lid at 200d C and wait it out. Could go on a bit of a rant about anticipation, and instant gratification, but I won't. You know what I mean here. Get the kids on another project to take their minds off "when do we open the kiln" huh? huh?

Yes. Yes, I know there are some people who push the envelope and open up a hot kiln and let it all happen. But you've got the kids' work in there and you've done a long slow bisque to ensure 100% success rate on these thickly made and no doubt riddled with air pockets precious pieces....What's another couple of hours?

[Lucille Oka]

You are in a perfect position to teach children to have a little patience. If they are in a hurry tell them if the kiln is opened too soon the pieces may be ruined so it is best to wait for them to cool down.
The best temperature to open the kiln is the same temperature they were when they went in, and that is room temperature. That way there is no 'ifs', 'ands' or 'buts' about it. If you find that you can't wait to open the kiln go read a book, make dinner, clean up the shop, watch a movie, start planting those petunias, there are a lot of things you can do while you are waiting for the cool down.
Don't rush it, you won't regret it.

[morah]

Lucille Oka, on 23 July 2012 - 09:51 PM, said:

You are in a perfect position to teach children to have a little patience. If they are in a hurry tell them if the kiln is opened too soon the pieces may be ruined so it is best to wait for them to cool down.
The best temperature to open the kiln is the same temperature they were when they went in, and that is room temperature. That way there is no 'ifs', 'ands' or 'buts' about it. If you find that you can't wait to open the kiln go read a book, make dinner, clean up the shop, watch a movie, start planting those petunias, there are a lot of things you can do while you are waiting for the cool down.
Don't rush it, you won't regret it.

[morah]

Thanks so much for your advice. I definitely agree in theory that it would be great to teach children patience. The problem is that the schedule the kids are on combined with the small kiln size make it extremely difficult to wait that long. I am expected to have them complete 2 projects a month which wouldn't be a problem if not for the fact that it is over 100 kids and a really small kiln. So I really need to turnover the projects as quickly as possible. So given that this is definitely not an ideal situation, I just need some guidance as to what temperature I can open the kiln without risking the projects. I have no problem taking them out using an oven mitt, I just don't want them to be destroyed. Is there a difference between bisque and glaze firing in terms of when I can take them out? Do I really have to wait for room temperature or can I take them out at 300 or 400 degrees? I really appreciate you sharing your years of experience with a beginner like me.

[morah]

Thanks so much for your advice. I definitely agree in theory that it would be great to teach children patience. The problem is that the schedule the kids are on combined with the small kiln size make it extremely difficult to wait that long. I am expected to have them complete 2 projects a month which wouldn't be a problem if not for the fact that it is over 100 kids and a really small kiln. So I really need to turnover the projects as quickly as possible. So given that this is definitely not an ideal situation, I just need some guidance as to what temperature I can open the kiln without risking the projects. I have no problem taking them out using an oven mitt, I just don't want them to be destroyed. Is there a difference between bisque and glaze firing in terms of when I can take them out? Do I really have to wait for room temperature or can I take them out at 300 or 400 degrees? I really appreciate you sharing your years of experience with a beginner like me.

[jeffkuratnick]

I usually stick with the 600d/F rule to stick a brick underneath the lid and vent the kiln for a while. Although you get some crackling, it is not very severe.

Additionally, you can do a newspaper test should you not have a pyrometer: Take a sheet and roll it on the long end - stick it inside a spy hole - if it ignites, the kiln is too hot to open - if it smolders you are in range to crack the lid and begin cooling the kiln down at a faster pace.

At about 300d/F I will typically open the lid fully without issue.

On a side note: If you're firing thicker work in a bisque kiln with manual or digital settings - be sure to spend extra time letting the kiln soak at 'Medium'. This (again, 600 d/F is crucial) is where carbon and chemical water begin to burn out of the clay body - if you move through the medium sequences too quickly - carbon and chemical water will trap itself inside the clay body resulting in an explosion - destroying someone's work.

Hope this helps!

[yedrow]

I've always waited till 450-500 deg. F. to crack the lid after you get through the cristobalite quartz inversion. That is about the temperature of a household oven. I open the lid at around 300 deg. F. That being said, space tends to be important for me and waiting can back things up, especially for bisque. Sometimes potters do have to hurry things along. I often pull bisque out that is so hot you have to let your gloves cool down between pieces.

[pricklypotter]

yedrow, on 23 July 2012 - 09:02 PM, said:

I've always waited till 450-500 deg. F. to crack the lid after you get through the cristobalite quartz inversion. That is about the temperature of a household oven. I open the lid at around 300 deg. F.

What yedrow said. Also keep in mind that the thermocouple may have its own measurement error and also that the temperature of different areas of the kiln can be different, and even of the tops and bottoms of the same pot. in essence, you want no part of the ceramic to undergo the quartz inversion (a phase transition, an abrupt volume change) too quickly or it may dunt. so allowing for temperature variation within pots and within the kiln, better play it safe. I pull the peeps at 250F and crack at 200F, open at 180F and unload at 150F or cooler. It's a community studio and we fire to cone 6.

[DAY]

morah, on 23 July 2012 - 07:20 PM, said:

Hi everyone! I am a newbie to this site and to ceramics in general. I've been giving ceramics classes to kids this summer and there is a lot of pressure to get the projects done. I have an L&L e23s electric kiln and I've been firing to 06 and 04. What temperature is it safe to open the kiln at for bisque and what temperature for glaze? The projects are relatively small and thick. thanks

This is one of those "it depends" questions. Too many variables for one answer to fit all. Trial and , unfortunately, error will teach you- and the kids- what you can and cannot do. A rule of thumb is the kitchen oven parameter; 300-400 degrees F, and use oven mitts.
You can speed the cooling, once you are below the inversion temp, by opening the bottom and top peepholes, to create a draft. Since you have an electronic controller, you can check the temperature at each thermocouple.

[Marcia Selsor]

I use a piece of paper to see if it will burn (451 F) ..well below quartz inversion ...at least in that section of the kiln. This is when I prop open the lid or begin slowly cracking open the door of a gas kiln.
Marcia

[Mudslayer]

This is what happens when you open your kiln before it is cooled sufficiently...i wait 12 hours after the kiln has turned off, I used to prop open between 200 and 300 degrees, but you can see from picture below, which was an entry in a contest, (not anymore), what happens when you open before you should. I NEVER EVER EVER open kiln before 150 degrees now, in summer, in winter i open 15 hours later and then the pieces go into a big oven cooking bag to keep them warm.

Try to find a good used kiln so you can have one to bisque in and one to glaze in. there are a lot for sale at very good prices... Patience is so very hard, but after I did this a few times, it is called shivering, i learned my lesson, if it is too hot to hold, you will have problems down the road.

this happened 4 days after it came out of kiln, that is how long it took the glaze to crack all the way around the yarn bowl.

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[morah]

Thank you all for good advice. Since you used some terms I never heard of I did some research and now I am beginning to understand what you are all telling me. To summarize it sounds like I should never, ever, no matter how much pressure I am under, open the kiln until it is lower then 500 df but it is risky to open it at even 400 or 300. Ideally, I should wait for room temperature. There is a greater concern for glaze firing then bisque. I am trying to convince the camp director to get me a bigger kiln, so I don't have to rush the cooling. I doubt it will happen, but we can always hope.

[JBaymore]

morah, on 24 July 2012 - 09:46 PM, said:

I am trying to convince the camp director to get me a bigger kiln, so I don't have to rush the cooling. I doubt it will happen, but we can always hope.

Hum... do the math.

Unless it is a charity situation........ 100 kids parents PAYING for camp each month. 100 kids enjoying getting fired ceramic works as part of that camp experience. What you are doing is part of the reason that they are THERE in the first place. Your efforts help generate the interest in the camp. You help bring in revenue.

Bigger kiln, the possibility of larger scale pieces or more output from the really interested kids (and hence more "camp experience satisfaction"). Bigger kiln, the lower the energy costs per pound of work fired. (In a periodic kiln like that a huge portion of the energy is use to heat the kiln structure itself plus the ratio of interior volume to wall surface for heat loss exchange goes in your favor.) The less time you spend loading and unloading a kiln is the more time you can spend on the important stuff like personally interacting with the kids.

best,

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

[morah]

Thanks John. Maybe I'll give the camp director a copy of what you wrote. If a bigger kiln would really save energy he might consider it- dollars and cents speaks.

[morah]

morah, on 26 July 2012 - 11:35 AM, said:

Thanks John. Maybe I'll give the camp director a copy of what you wrote. If a bigger kiln would really save energy he might consider it- dollars and cents speaks.

I just wanted to give you all an update: I spoke to the camp director and mentioned all of John's points and he asked me to look into the cost of adding a ring to my existing kiln! Of course I immediately got him the info. It isn't cheap, but definitely less then another kiln. He didn't say no outright, so I am hoping. I'll try to keep you posted!