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What bisque firing schedule do you use?


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#1 MichaelP

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Posted 24 March 2013 - 05:26 PM

Different books and Internet sites give different schedules. I realize that the schedule depends of quite a few parameters (type of clay, size of the items, etc.), but it would be interesting to see what schedules you use with a mentioning of what clays you fire this way, etc.


At this time I'm, mostly, interested in firing different types of stoneware in electric kilns.


By the way, could you recommend a really good book(s) on using electric kilns in studios? Something that gives good practical suggestions on choosing clay, underglazes and glazes, describes different technics that can be used with electric kilns, etc.



Thank you.

#2 Chris Campbell

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Posted 24 March 2013 - 07:56 PM

Two good basic reference books are :
Mastering Cone 6 Glazes by Ron Roy and John Hasselberth
A Studio Handbook by Vince Pitelka

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#3 Benzine

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Posted 24 March 2013 - 08:16 PM

It also depends on what type of kiln you have as well. Manual with the "Low, Medium and High" twist nobs, or a computer controlled model. I'm guessing the former, as opposed to the latter.
"Anything worth believing, is worth questioning"

#4 MichaelP

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Posted 24 March 2013 - 08:44 PM

It also depends on what type of kiln you have as well. Manual with the "Low, Medium and High" twist nobs, or a computer controlled model. I'm guessing the former, as opposed to the latter.

Wrong! The latter. :)

Two good basic reference books are :
Mastering Cone 6 Glazes by Ron Roy and John Hasselberth
A Studio Handbook by Vince Pitelka

The orders have been placed. Thank you, Chris.

#5 MichaelP

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Posted 26 March 2013 - 12:34 AM

Looks like bisque firing schedule is a closely guarded secret. :)

#6 Mark C.

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Posted 26 March 2013 - 01:52 AM

Looks like bisque firing schedule is a closely guarded secret. Posted Image


I bisque fire a few times a year in a 10 cubic electric when the gas kiln is going.
I load it full full to the brim with bone dry pots and dial the fireright controller to 5 hours-in 5 hours the kiln will be on high on all three levels and goes off in about 8 hours altogether for the whole cycle-thats a cone 08 bique of porcelain.I have shortehed this to 7 hours afew times as well. I like a slow cool down.
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#7 Natania

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Posted 26 March 2013 - 05:26 AM

I have the old fashioned dials (my ipad just wrote "ideals" for me instead of dials, which i also hope i have!).I set the kiln to low for two hours, med. for two and high for two, it usually shuts off in 4-6 hours from setting it on high. I go slow because I've got a very dark brown cone 5 stoneware body that does better with a slow firing. Hope this helps!

#8 Doulla

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Posted 26 March 2013 - 05:58 AM

I sculpture with stoneware clays and use the following schedule for bisque firing which is one of the preset programs that came on my electric kiln.

60 or 90 ramp depending on how large the piece is. I use 90 most of the time even on larger pieces.

It ramps at these until reaching 600 degrees centigrade and then continues at 250 ramp to the final temperature. I use 1,000 - 1,060 for my final bisque firing temperature.

I have lots of pottery books but none of them really talk about the firing process in any detail so I got most of what I know from the manual with my kiln. I have been following this schedule for over 10 years and have never had a problem.

#9 OffCenter

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Posted 26 March 2013 - 06:08 AM

For a normal load (meaning nothing extra large and/or thick), I fire on low about 240 F. to make sure I'm well past the boiling point then turn the kiln on high.

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#10 Mesi

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Posted 26 March 2013 - 08:15 AM

I have lots of pottery books but none of them really talk about the firing process in any detail so I got most of what I know from the manual with my kiln. I have been following this schedule for over 10 years and have never had a problem.




I would LOVE for someone to write a detailed guide on firing. As a potter who is fairly new to firing my own work, it's been a tough road trying to figure out what I'm doing. And I, like the OP, have a kiln with a sitter and only the vaguest idea what the cryptic knobs equate to. Its difficult to translate that into a ramp of x degrees per hour, if you don't know what each knob setting does. So far I've just had to wing it, and have had passable results.

#11 MichaelP

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Posted 27 March 2013 - 01:00 AM

Thank you, guys and girls.


One of the grey spots, as I see it, is the fact that the speed of unrestricted temperature increases varies greatly from kiln to kiln. It depends on the physical size of the kiln (or, more precisely, power per volume like Watts per cu.ft), insulation, etc. Ramping up or down is very hard on relays, so the more we allow the kiln to raise or drop temperature at its own pace, the less relay switching cycles it will require. At the same time, if we eliminate ramping, a small kiln may reach the max temperature within 30 minutes whereas large kilns may require 5 hours.. That's why "I use no ramping" may mean 2000-degrees per hour or 200-degree per hour. In the first case it'll be just a very quick heating, in the second case it will be a "natural ramping".


Just thinking out loud. :)

#12 Pres

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Posted 27 March 2013 - 01:30 PM

Thank you, guys and girls.


One of the grey spots, as I see it, is the fact that the speed of unrestricted temperature increases varies greatly from kiln to kiln. It depends on the physical size of the kiln (or, more precisely, power per volume like Watts per cu.ft), insulation, etc. Ramping up or down is very hard on relays, so the more we allow the kiln to raise or drop temperature at its own pace, the less relay switching cycles it will require. At the same time, if we eliminate ramping, a small kiln may reach the max temperature within 30 minutes whereas large kilns may require 5 hours.. That's why "I use no ramping" may mean 2000-degrees per hour or 200-degree per hour. In the first case it'll be just a very quick heating, in the second case it will be a "natural ramping".


Just thinking out loud. Posted Image


Other factors in the mix are the thickness of the lid, the condition of the elements, the outside ambient temperature. I have been firing a kiln for 30 years now with no kiln setter. It fires faster now than before since I put a new lid that is one inch thicker than the old one; cool down is also slower. I fire by color of heat, and cones for shut off at ^06. Usually 3 hrs of watersmoke in Winter; two in Summer unless high humidity. Firing takes around 7 hrs, then shut down with low switch on low setting before new lid, now shut down complete. Open kiln 18 hrs later when all cool.

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#13 oldlady

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Posted 27 March 2013 - 05:40 PM

good question!

as many answers as potters firing. answering for someone truly new to this and assuming they have a manual kiln i offer the following.

my first kiln, a paragon electric about 18 inches inside diameter and about 18 inches deep, came with an instruction book when i bought it in 1972. it said to put the bottom switch on low for one hour followed by the middle switch on low one hour later and the top switch on low one hour later. lid propped an inch and all peephole plugs out.


then follow the same sequence with the medium switches and at the end of the six hours since the beginning, start putting the high switches on. at that point check for possible water vapor leaving through the peepholes and the top using a mirror to see if it clouds up. finding NO steam on the mirror, proceed. once the bottom high switch goes on, the peephole plugs go in and the top is closed. do not burn yourself at this point and carefully lower the top with a long, strong metal tool so you do not bang it closed. removing the prop is tricky too, be prepared to get it safely to a safe surface until it cools. kitchen tongs, long ones, work here. they will bend if you try to use them to lower the lid.


the firing after all the switches are on high should only be a few,( 3- 5) hours depending on your element's age and condition. i fire to cone 04 these days since losing 3 loads to underfired bisque in 1990. have never had anything go wrong using this schedule even now with a much bigger automatic kiln fired to cone 6 with raw glazed work and the occasional refire on a piece i didn't like all in the same firing. now that i said that watch what will happen to the next one!!

here in florida i have a smaller manual kiln with a timer as well as a kiln sitter. never having a timer i set it for 10 hours the first time i fired this used kiln and learned that 5 hours is enough. have no idea of the element's condition. though i prefer to spray glaze and fire raw, i have to bisque here and take everything north to glaze it at home in a larger space.


hope this helps someone new.OOOHHH! YES!!! if you are new, start right and keep a log of exactly what you do so if anything happens you can repeat or avoid it.
"putting you down does not raise me up."

#14 MichaelP

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Posted 29 March 2013 - 12:02 AM

Very helpful additions. Thank you, Pres and Oldlady.

#15 Benzine

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Posted 29 March 2013 - 07:56 AM


It also depends on what type of kiln you have as well. Manual with the "Low, Medium and High" twist nobs, or a computer controlled model. I'm guessing the former, as opposed to the latter.

Wrong! The latter. Posted Image

Two good basic reference books are :
Mastering Cone 6 Glazes by Ron Roy and John Hasselberth
A Studio Handbook by Vince Pitelka

The orders have been placed. Thank you, Chris.


That's what I get for making assumptions......


I've used two different computer controlled kilns (A Skutt and a L&L) and one type of manual controlled kiln (Also a Skutt) since I've been teaching. With the manual kiln, I just followed the scheme, my predecessor used. For the Skutt, I used a program, the manual recommended. For my current L&L, I used a variation of that program. I entered it almost two years ago, so I'm have a tough time remembering, exactly how I have it set. I know the first portion, ramps up at 50 F per hour to 200 and holds for four hours. Then I have it go to 500 F and hold for two hours, but I forget the rate. Then it ramps up at 500 F to Cone 04.

Using this setting, it's rare, that I lose a student's project. Usually, if there is a loss, it's because it was super thick, not vented, or they just gave themselves no time to let it dry all the way, and had to risk it, in order to get it done in time.
"Anything worth believing, is worth questioning"

#16 MichaelP

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Posted 31 March 2013 - 11:33 PM

Benzine,

First of all, thank you for your kind assistance.

What model or size of L&L do you have? How long does it take to heat it to cone 04, and how long it cools down?
Do you find that busquing stoneware to cone 04 is preferable to 05 or 06 for any reason other than the fragility issue? Do you find stoneware bisqued to cone 04 accepts underglazes, stains and glazes as perfectly as cone 05/06 bisque?

Thank you.

#17 Benzine

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Posted 01 April 2013 - 09:20 AM

Benzine,

First of all, thank you for your kind assistance.

What model or size of L&L do you have? How long does it take to heat it to cone 04, and how long it cools down?
Do you find that busquing stoneware to cone 04 is preferable to 05 or 06 for any reason other than the fragility issue? Do you find stoneware bisqued to cone 04 accepts underglazes, stains and glazes as perfectly as cone 05/06 bisque?

Thank you.


I'll have to check the model, when I go to the school tomorrow, I'm off today.
With the program I use, it takes about fifteen hours. Six of those hours, are holding points, namely the four hours holding at 200 F. The last bit of the firing goes relatively fast.
I generally set the kiln to fire the afternoon before. I'll put it on a delay, to start about midnight, with the candling portion. That way, the kiln isn't hot, when I'm not there. By the time I get to the school in the morning, it's finishing up the second hold point around 500 F It usually finishes early to mid-afternoon. By the time I come in the next morning, the kiln is cool enough to open and unload, which would be around fifteen hours later.

In my current classroom, I do not use stoneware, only low fire white. However, in one of my previous classrooms, I did use stoneware. There, I bisque-fired to 05, and found the clay accepted underglaze, just as well as glaze. I will say however, I heavily encouraged the students to use underglaze before the bisque firing. I found there to be less issues, when they went to apply the clear by doing so.

I'm sure there are others, who can offer more information on the difference between firing to 04, 05 and 06, as I've only got experience to firing to 05, when it comes to stoneware.
"Anything worth believing, is worth questioning"

#18 MichaelP

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Posted 01 April 2013 - 05:36 PM

Benzine,


Thank you.

#19 Benzine

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Posted 03 April 2013 - 10:13 PM

Michael, my classroom kiln is a L&L model JD236.
"Anything worth believing, is worth questioning"

#20 MichaelP

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Posted 04 April 2013 - 08:18 AM

Thank you. I appreciate it.




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