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Is This Too Fast To Fire?

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I have been trying to find a shorter bisque firing schedule, currently I take 16 hours with bone dry ware.  The following has been recommended to me.  Do you think it is safe?  or too fast?

Ramp 1 150* per hour to 200  hold 2 hours

Ramp 2 200* per hour to 700* hold ??

Ramp 3 100* per hour to 1,000*, no hold

Ramp 4 300* hour to 1925* hold 30 minutes

This  is a 13 hour total.

 

Some of this was from a more experienced potter, with guidance from Hamer and Hamer's book.

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I use the pre-programmed Cone 05 slow bisque program in my L&L kiln:

 

80 degrees/hour to 250 degrees

200 degrees/hour to 1000 degrees

100 degrees/hour to 1100 degrees

180 degrees/hour to 1641 degrees

80 degrees/hour to 1891 degrees; hold for 5 minutes

 

Firing time is just under 14 hours. Kiln vent is turned on at start; turned off when I unload.

 

I only use a hold at 200 degrees if the wares are not dry. If you know your load is dry, there is not need for a hold at 200 degrees. When I fired kilns at a community studio, we did a preheat to 200 degrees because students put damp items on the bisque shelf and there was a variety of wall thicknesses in wares. At home, I seldom feel a need to preheat.

 

Slowing down the rate of temperature rise at the end allows for the crud to burn out (same reason for slowing from 1000 to 1100 degrees).

 

You can go faster climbs of temperature in-between, but a slow start to remove physical water, slow around 1000 to 1100 to remove chemical water, and slow at end to burn out crud seems to be key.

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I have a programmed computer and my dry bisque firings run between 6-8 hours depending on whether I am doing a Cone 010 or 06. They call this their medium speed setting.

16 hours sounds too long for a load that is dry ... That is about the length of a Cone 6 firing for me.

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How thick are your pieces, sculpture or pots? Type of clay used, is it a cleaner firing porcelain or does it have lots of carbon bearing stuff to burn out? Do you run a vent, cram your bisque or is it loosely loaded? Like everything with clay I don't think there is one correct answer, it depends...  If you have problems with pinholes in your glazed wares this has a strong possibility of being caused by either bisquing to fast or not enough venting with the bisque. Pots might not blow up in a fast bisque but carbon needs to burn out.

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I have been trying to find a shorter bisque firing schedule, currently I take 16 hours with bone dry ware.  The following has been recommended to me.  Do you think it is safe?  or too fast?

Ramp 1 150* per hour to 200  hold 2 hours

Ramp 2 200* per hour to 700* hold ??

Ramp 3 100* per hour to 1,000*, no hold

Ramp 4 300* hour to 1925* hold 30 minutes

This  is a 13 hour total.

 

Some of this was from a more experienced potter, with guidance from Hamer and Hamer's book.

Assuming that you are firing thrown ware, for me this program is too slow.  If I fire bisque with the bisque program, I use fast bisque no hold. If I fire with my own program , it is ramp @ 200 to 200 hold 30 minutes, ramp 300 to 1000 hold 5, ramp 250 to 1200 hold 10. step to 1680 hold 5, ramp 80 to 1830 hold 10, off. I bisque at 06. If I think things are not bone dry I use the preheat and hold10 to 30 minutes.

David

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Clay is a mixture of 3 different types of stoneware. combination of thrown and hand built, not thick or heavy, no student work in this load.  I don't have any problems with the schedule I am using, no pinholes or glaze dipping problems .   I pack the bisque pretty tight, but only stack bowls and such 3 deep.  I'm afraid of cracking the ones on the bottom of a deeper stack.

The program I use was giving to me by a really cautious teacher and it work for me, but I am wondering if it is all necessary.

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 I think Skutt's med schedule is:

 

1 200 ºF/HR 250 ºF 0
2 400 ºF/HR 1000 ºF 0
3 180 ºF/HR 1150 ºF 0
4 300 ºF/HR 1694 ºF 0
5 120 ºF/HR 1946 ºF 00.05
 
I would gradually make changes to your schedule to speed it up and see how it goes.

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I'm using a non computer kiln my bisque runs 11 hours, 12 if it is a tight pack. Work is thrown and handbuilt, nothing overly thick and everything has to pass the cheek test before it goes in so no wet ware. Not sure if this helps with your computer firing.

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I recommend to my customers that they bisque fire using the 'Fast Bisque' setting on an L&L, 'Medium' on other brands. It works fine for most pieces. If you're firing large or thick pieces, then use the 'Slow' setting. I often bisque fire on the 'Fast Glaze' setting, which takes just under 5 hours, and I've never had problems. I don't generally recommend bisque firing that fast, though.

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I normally have a long cautious water-smoking period at the beginning of my bisque. However these posts make me wonder how long does it actually take to steam all the water out of the pores of an average pot? How long does that water smoking period really have to be? I know a lot of the answer must be "it depends" but would be interested if anyone has a more definitive answer assuming "all else equal"

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If the pot is dry, there's no need to do any preheat. There's also no need to do any holds during any of the ramps. I would slow down the last couple hundred degrees to 180 per hour or less, though, to make sure everything is getting burned out well.

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