Firing Unglazed Containers

Colorado

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This is probably a stupid newbie question….but my question is:

When firing unglazed containers, is there any need/advantage to doing a bisque fire before the final fire to cone 5? Or do you just do a single firing for unglazed?

@NaoTK @Sansokuu @penumbra @Pitoon @JeffS73 or anyone else!

Thanks!
 

Sansokuu

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When firing unglazed containers, is there any need/advantage to doing a bisque fire before the final fire to cone 5? Or do you just do a single firing for unglazed?
Nope! You can do a single firing. Just take the usual precautions, make sure the greenware is as dry as possible plus a long and slow candling. The speed at which you ramp up to the final cone should be on the slower side as well. We single fire our unglazed. Which is nice, since glazing stuff is such a pain lol.
 

penumbra

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I always fire bisque to cone 06 and occasionally cone 04 prior to my glaze firing at cone 6 and occasionally cone 8. I don't like handling greenware any more than I have to. Also, there is almost no out-gassing when refiring and it eliminates pock marking. I know plenty of people who do single firing but across the board, if you are using various clays and reclaimed clays, two firings is the way to go. Should mention also that I do a lot of oxide washes so I need a bisque fired piece to hold up to all that abuse.
 

NaoTK

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(eating breakfast!) it depends on the clay...

If your clay sources its iron from a natural high-iron "fire clay", then it probably contains iron sulfides (pyrite) from which the iron originates. If the sulfides are not burned out in bisque, then they will remain in the final firing and the gases they exhaust will act as a strong reducing agent. This is what causes black coring and leads to brittle pots and high thermal expansion. If your pot is small enough then you don't care.

If your clay gets its iron from added iron or the iron content is low, or the clay is very open, then its not necessary to bisque. Most western clays are like this.
 

ABCarve

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An electric bisque firing slows down when going through quartz inversion. 1000-1100F.
 

mrcasey

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Not matter how careful I am with smoothing the greenware, I often get little burrs that don't become apparent till after the bisque. After the bisque firing, but before the final firing, I can take sandpaper (while wearing n95+ mask) and smooth off sharp edges, burrs, etc.
 

sorce

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It is completely dependent on the firing schedule.

However, a proper bisque firing should be slow and long enough to be a proper bisque firing, which means adding more slow and a little longer on to the end of it, is what you should be doing anyway.

Storing large amounts of preglazed ware (industry) is the only reason we ever started bisque firing. In England, hence, bisque.

Being able to glaze them more aggressively is secondary to that.

Many problems that occur with firing is because people think a bisque firing is only to make pots easier to glaze.

The physics and chemistry says that while possible, a slow long bisque fire and a fast glaze firing isn't the best way.

Everything should be slow and long because you are AGAIN passing through quartz inversion, turning beta quartz into alpha quartz and back.

This is why I opt for the most efficient method of single firing.

One change, less cristobolites (sp) stronger wares....period.

Sorce
 

penumbra

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The main thing is my friend, find out what works for you. Every defeat is a victory.
Don't trust any answer that claims to be the only "right" way.
There is a very well known raku artist that typically fires a single piece up to six times and he produces amazing ware. Would I do this? Probably not. But I must say that his work is far better than mine. Of course raku is at much lower temperatures that most of us would consider bisque. Still, just saying don't trust anyone with all the answers. And though you may find "textbook" advice, it is not the same as "hands on" advice.
One thing most (certainly not all) potters agree on is that slow is best in all firing stages but particularly bisque. But I know a certain well known raku artist from Hawaii who can throw a pot in the morning and fire it in the afternoon.
 

JeffS73

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I have less experience than most of those replying, MrCaseys response is useful, you can use bisque to finesse your work.

I use single fire when I can, primarily because it's efficient, but currently I bisque for glazed work. I've recently had small successes single firing glazed, but there's a lot more to think about for this route.

Whether you single fire or bisque, you need to take it slow up to about 900c when a pot is FIRST fired. Both my bisque and single fire programs go: 30c/hr ramp to 80c, 12hr candle at 80c (I.e. hold), 100c/hr ramp to 700c, 34c/hr ramp to 950c, then either off for bisque, or onwards and upwards at whatever my kiln can manage :)

Horselover and Sorce helped me understand all this. Lots of info on black coring in Hamer.

I don't know about your clay, but wax your pots feet.
 

Colorado

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The main thing is my friend, find out what works for you. Every defeat is a victory.
Don't trust any answer that claims to be the only "right" way.
There is a very well known raku artist that typically fires a single piece up to six times and he produces amazing ware. Would I do this? Probably not. But I must say that his work is far better than mine. Of course raku is at much lower temperatures that most of us would consider bisque. Still, just saying don't trust anyone with all the answers. And though you may find "textbook" advice, it is not the same as "hands on" advice.
One thing most (certainly not all) potters agree on is that slow is best in all firing stages but particularly bisque. But I know a certain well known raku artist from Hawaii who can throw a pot in the morning and fire it in the afternoon.

Yes I am looking forward to figuring out what works best for me! Maybe I’ll try it both ways and just see how it goes :)
 

Pitoon

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This is probably a stupid newbie question….but my question is:

When firing unglazed containers, is there any need/advantage to doing a bisque fire before the final fire to cone 5? Or do you just do a single firing for unglazed?

@NaoTK @Sansokuu @penumbra @Pitoon @JeffS73 or anyone else!

Thanks!
I bisque everything. While you can run 1 firing on unglazed pots, I put too much time in to have one explode and ruin everything on the shelf.
 

ABCarve

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ABCarve

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This is a guy I went to university with, Bill Campbell. His pottery was sold around the world and he had 30 employees. He too, only single fired. He used electric kilns and would soak for hours a max temperature to insure off-gasping.

Single firing is something you need to read about, try and experiment with. It’s a commitment you need to take if you truly want to understand it. Personally I have been put into a position that it would be very convenient for me to single fire a pot along with some other bisqued pots and was seriously pondering it. I chose not to for the risk/reward ratio.
 

HorseloverFat

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Even my glazed pieces just get fired once! *Evil laugh"🤣🤣

I'm a raw-glazer... I've done it both ways, there are advantages to both schools of thought.... Raw glazing has just worked the best (and ironically, at first, the WORST) for ME, personally.

Buuuuut... Before glazing... My greenware gets at least one oven-drying session... 8-10 hours at 185dF
 

HorseloverFat

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This is a guy I went to university with, Bill Campbell. His pottery was sold around the world and he had 30 employees. He too, only single fired. He used electric kilns and would soak for hours a max temperature to insure off-gasping.

Single firing is something you need to read about, try and experiment with. It’s a commitment you need to take if you truly want to understand it. Personally I have been put into a position that it would be very convenient for me to single fire a pot along with some other bisqued pots and was seriously pondering it. I chose not to for the risk/reward ratio.


EXACTLY!!! definitely not for everybody, and a huge learning curve... Far more risk for the first couple YEARS of experimentation...

It really is 'it's own beast'... That by the time you learn SEMI-fluently... You are already COMMITTED..

I think you said this very well.
 

ABCarve

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A very lucid pondering .


A have only one Bill Campbell pot in my collection. It is a crystalline glaze.
When I was in college with him, he was in his mid-40s (1972-76) and he was foolin’ with those same glazes. We all asked, “hey, who’s the old guy”. When I went back to school to reintroduce myself to ceramics I was 55. I can only speculate on what my fellow students were pondering. Bills glazes have all evolved with amazing results. His pottery is nearby, although now closed because of his recent retirement. Edinboro has an extraordinary ceramic dept. 5-star although it’s going through a drastic restructuring currently. Not sure it will end well. 😢 I can give you a first rate tour if you come for a workshop this spring.
 

penumbra

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When I was in college with him, he was in his mid-40s (1972-76) and he was foolin’ with those same glazes. We all asked, “hey, who’s the old guy”. When I went back to school to reintroduce myself to ceramics I was 55. I can only speculate on what my fellow students were pondering. Bills glazes have all evolved with amazing results. His pottery is nearby, although now closed because of his recent retirement. Edinboro has an extraordinary ceramic dept. 5-star although it’s going through a drastic restructuring currently. Not sure it will end well. 😢 I can give you a first rate tour if you come for a workshop this spring.
Thank you for that offer my friend. I hope it will happen.
 
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