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#1 meisie

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Posted 09 May 2014 - 05:56 PM

I have been bisqueing the  clay I have to cone 04 per the instructions on the box. The glaze being low fire is fired to cone 05. 

Can I combine a glaze and bisque firing? would it make a difference if the clay is bisqued to 05? Would it still take glaze? I'm thinking yes but not really sure. 

Thanks



#2 Babs

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Posted 09 May 2014 - 07:52 PM

C05 is lower than C04 therefore your ware will take the glaze and as your pots will be more porous you will have to test the glaze uptake, your glazes may have to be made thinner.

The lower firing of your bisque may cause trouble in the end result but pos. not. So test and see.

The combining of the bisque and glaze may cause temp variations within your kiln as the bisque is usually much more densely packed than the glaze ware. Again test and see if you like what you get, but your pots at the end will not be as vitrified.



#3 Benzine

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Posted 09 May 2014 - 08:41 PM

I've know quite a few people, especially teachers, who will do this with low fire wares. I've done it myself with no big issues. The biggest problem, was tht when a student project was thicker than anticipted, and exploded, sending pieces of bisqueware onto the glazewre, where'd they stick. But if pieces are dried fully, it's not an issue.
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#4 bciskepottery

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Posted 09 May 2014 - 08:49 PM

I think the reason for bisque firing low-fire clay at a higher temperature than glaze is to allow the higher bisque to burn out any contaminants that could otherwise mess up the glaze firing at the lower temperature (outgassing, etc).

If you try a combined firing, separate bisque and glaze items on different shelves; don't mix on the same shelf -- that way you can avoid any cross contamination.

Unless your clay body vitrifies at cone 04 (which seems unlikely), then your wares will be porous whether bisque or glaze fired to 04 or 05. Bisque firing to cone 04 will make them less porous than if only fired to cone 05 (but probably no where close to vitrified in either case).

#5 neilestrick

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Posted 10 May 2014 - 08:47 AM

Some people claim that if you bisque and glaze at the same time that it will screw up certain glaze colors, like reds. I've never seen it happen. And like Benzine said, explosions can be a real mess. If you are worried about explosions, put your greenware on the bottom shelves, glaze ware on the top shelves. That way if anything blows it won't get on the glazes.


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#6 Colby Charpentier

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Posted 10 May 2014 - 09:04 AM

Some people claim that if you bisque and glaze at the same time that it will screw up certain glaze colors, like reds. I've never seen it happen. And like Benzine said, explosions can be a real mess. If you are worried about explosions, put your greenware on the bottom shelves, glaze ware on the top shelves. That way if anything blows it won't get on the glazes.

 

This is an interesting circumstance. Yes, the glaze ware on top would ensure most explosions in the bisque wares wouldn't get up to the glaze wares, however the preheat would be less effective on the bisque wares. During the preheat, there isn't much radiating heat to help distribute the heat throughout the kiln, meaning that the rising heat concentrates in the upper portion of the kiln. Because of this, wares that are lower in the kiln can receive less benefit from the preheat.

 

This is relevant while using a preheat to "cushion" the bisque wares. Another equally valid solution would be to use a longer preheat with the bisque on top to make sure all moisture is evacuated. I personally like Neil's suggestion of bisque on the bottom, I'm just trying to make the point that adequate drying is vital to successful firings involved both glaze and bisque wares. 



#7 JBaymore

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Posted 10 May 2014 - 09:25 AM

Some people claim that if you bisque and glaze at the same time that it will screw up certain glaze colors, like reds. I've never seen it happen.

 

Before the prevalance of encapsulated cadmium stains in red and pink and other such glazes .... the lead based low fire cadmium sulfide (CdS) based reds were susceptible to the sulphur dioxide given off by bisque firing clay.  Hence the "admonition". 

 

best,

 

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


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#8 Benzine

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Posted 10 May 2014 - 10:04 AM

your greenware on the bottom shelves, glaze ware on the top shelves. That way if anything blows it won't get on the glazes.


I've unfortunatley found out, that even putting greenware on different shelves, won't prevent the problem. That's why I have really moved away from mixing loads, unless I absolutely have to.
"Anything worth believing, is worth questioning"

#9 meisie

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Posted 10 May 2014 - 02:15 PM

Thanks for all the replies. It's something I started thinking about because the other teacher who is attempting to do clay with her students forgot to give me a class that should have been bisqued with the others. ( I have the kiln in my classroom) So I have 25 pieces that are not bisqued and the rest ready for a glaze firing.  I understand that with the low firing that this clay never fully vitrifies. It's elementary school so all the pieces are decorative.  Even if I bisque them with the glaze firing I am still going to need to put them in the kiln on their own when they are needing to be glazed so no matter what I won't have a full kiln with at least one firing. She drives me a bit crazy. She doesn't always listen or sometimes she just doesn't get it. 

 

I was doing mosaics and she wanted to try. I gave her a list of the materials she needed and said I would show her how to use them. She came back with items that home depot told her were what she really needed. I said well then you're on your own because I don't have a clue what this stuff is for.....???



#10 TJR

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Posted 10 May 2014 - 05:17 PM

I've know quite a few people, especially teachers, who will do this with low fire wares. I've done it myself with no big issues. The biggest problem, was tht when a student project was thicker than anticipted, and exploded, sending pieces of bisqueware onto the glazewre, where'd they stick. But if pieces are dried fully, it's not an issue.

Ben;

I bisque at 07, and glaze at 06 in my high school classes. If I have partial loads, I put the bisque ware on the bottom, and work to be glazed on a top shelf and fire the entire load at cone 06. Works fine. I don't put greenware and glaze ware on the same shelf ever.

Tom.



#11 Benzine

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Posted 11 May 2014 - 07:35 AM

Meisie, firing the second load of glaze, will take up more space, because you won't be able to stack wares, like in the bisque. So it might not be as much of a partial load, as it seems.

Also, I think every Art teacher/ teacher in general, can relate to colleagues, who "Just don't get it". Some are set in their ways and/or don't like admitting they need help or don't know something.

Tom, I don't put glazed bisque and greenware on the same shelf....anymore. But even recently, when I separate them, I've still had bits jump shelves. Not enough offerings to the Kiln Gods I guess....
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#12 Pres

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Posted 11 May 2014 - 09:46 AM

I would often mix loads at the HS. However, this would only happen at crunch time at the semester end. I had a rule that the pots had to be completed by a certain due date, and then glazed by a certain due date. As such, sometimes the two due dates would cause a problem if the pot was not completely dry because of weather, size, or other reason. In these instances I did some crazy things. First as I would be firing glazes or bisques every day I would place pots that were not completely dry on the top of the kiln to rest while the kiln was firing-nothing heavy mind you.

 

Then these would get loaded in the next load, usually a mixed load. The mixed load would always be separated by shelves, usually a full shelf between with the bisque being in the bottom. The glazed wear would start on the level above the full shelf. I would fire the load like a bisque load and then go to glaze temp turning down the bottom elements after red orange heat. This would usually do quite well, and even though we the glazes would have a tough time on the higher temp bisque, it was doable when they were warm. I always told the kids the dangers of glazing over the vitrified clay, but if you know kids. . .  In the end it worked, but was not the best of solutions for mid range stoneware. Don't do it at home, but then I never have that sort of crunch time.


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#13 neilestrick

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Posted 12 May 2014 - 09:43 AM

 

Some people claim that if you bisque and glaze at the same time that it will screw up certain glaze colors, like reds. I've never seen it happen. And like Benzine said, explosions can be a real mess. If you are worried about explosions, put your greenware on the bottom shelves, glaze ware on the top shelves. That way if anything blows it won't get on the glazes.

 

This is an interesting circumstance. Yes, the glaze ware on top would ensure most explosions in the bisque wares wouldn't get up to the glaze wares, however the preheat would be less effective on the bisque wares. During the preheat, there isn't much radiating heat to help distribute the heat throughout the kiln, meaning that the rising heat concentrates in the upper portion of the kiln. Because of this, wares that are lower in the kiln can receive less benefit from the preheat.

 

This is relevant while using a preheat to "cushion" the bisque wares. Another equally valid solution would be to use a longer preheat with the bisque on top to make sure all moisture is evacuated. I personally like Neil's suggestion of bisque on the bottom, I'm just trying to make the point that adequate drying is vital to successful firings involved both glaze and bisque wares. 

 

 

Not sure how this is any different than a regular bisque firing. You'd have green pots on bottom and the potential for explosion either way.


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#14 ashraf elhamy

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Posted 12 May 2014 - 03:42 PM

You can first try water absorption test on the bisque piece
If it's low , thus it will not take glaze
And vice versa

#15 TJR

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Posted 12 May 2014 - 06:01 PM

You can first try water absorption test on the bisque piece
If it's low , thus it will not take glaze
And vice versa

What do you mean low? Everything is fired to cone 06. Glaze and bisque. No point bisquing to 04.

Tom.



#16 Benzine

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Posted 12 May 2014 - 09:01 PM

Tom,

I bisque our low fire clay to 04, as that what the commercial glazes, I use, suggest.
"Anything worth believing, is worth questioning"

#17 Babs

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Posted 12 May 2014 - 09:51 PM

Tom,

I bisque our low fire clay to 04, as that what the commercial glazes, I use, suggest.

Benzine, like Tom I still bisque to C06 , though initially I bisqued to C08. As I do not get any pinholing or other probs of a low fired bisque I do not see the necessity to go higher. If your glazes are coming in liquid form then they will be thicker,than I use on my low fired ware, ( to enable a sufficient uptake of glaze by the less porous body). Maybe you do not need to go to C04?? Take a few hours off yur day!I

I would think that the cone to which one fires bisque is more related to the clay body than the glaze.... right??



#18 ashraf elhamy

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Posted 14 June 2014 - 10:54 AM

Dear TJR, what I understand is (meisie) want to put sprayed clay in firing without getting bisque the clay first
and I just say it will not give the same result
And if the clay is bisque at cone 5 the porous are v.small and will not take any more glaze

#19 Babs

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Posted 15 June 2014 - 03:11 AM

Mr Ashraf Elhamy I think Meisie wrote C05 not C5. As C05 and C04 are very close in temp required, there will be very little difference in porosity  as C04 requires a slightly higher temp to bend, it wil give pots with slightly less porosity, and so as stated above, there would be little difference and  the points above noted should give ok results.                                     



#20 clayfeetpottery

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Posted 25 July 2014 - 10:08 AM

Just an aside...I was letting semi wet works sit in my kiln room to dry before bisque firing them and my Kiln techsaid  this was creating too much moisture in the kiln room- which is why the outside metal on the kilns were rusting.  Just worth noting!


-with dirty feet and happy hands,

 

   Mel

 





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