How Much Warping To Expect In Bisque Fire

[Isculpt]

I've been following the topic regarding How tightly to pack a kiln with wares. My work is irregularly shaped (12" to 24" sculptures).  I've considered loading the kiln as tightly as possible, but I fear that I may end up with warped bottoms on my sculptures if I fire them lying on their sides instead of standing on their bases.  How likely is that to happen?  I'm firing raku clay (cone 06-2) at a bisque temp of no higher than 04. 

 

Jayne

[Min]

I think you would have to try it to see. If I fire my platters/ plates on their edge to ^04 they will warp, (porcelain like ^6 clay) but I know a lot of people do fire like that and have no warpage issues. If you bisqued to a lower ^ I don't think it would be a problem, in the ^010 - ^08 range. Just my 2 cents worth, I'm sure many people will disagree.

 

Min

[Mark C.]

If they are dry -almost zero chance.

I have never had a pice warp in a bisque that was dry.If still wet that is another story.

I have electric bisqued fired 16-18 inch porcelain platers on edge with no issues.

The only time I have had any warping is piles of wet spoonrests warping under wieght on many others when I loaded them wet. They still flattened straight at cone 11.

Mark

[Marcia Selsor]

You shouldn't get any warping if you fire them right. I fire my 24 " slabs of raku clay on edge and they don 't warp.

make some 1/4" coils for them to sit on. Arrange the could in a sun bust pattern. .that will let them move as they shrink and let any steam out the bottom and heat circulate.. I fire my bird bath stems and columns that way. no warping they are 24-28 inches.

Marcia

[Benzine]

If they are dry -almost zero chance.

I have never had a pice warp in a bisque that was dry.If still wet that is another story.

I have electric bisqued fired 16-18 inch porcelain platers on edge with no issues.

The only time I have had any warping is piles of wet spoonrests warping under wieght on many others when I loaded them wet. They still flattened straight at cone 11.

Mark

Mark,

 

When you say "Wet" how wet are we talking?

 

And just out of curiousity, if they were borderline bonedry, but with some water why could they warp, when fired?

[Min]

 

I have electric bisqued fired 16-18 inch porcelain platers on edge with no issues.

 

Mark

 

Okay, I must be doing something different. When I tried this I had the platters cup slightly. I stood the platters on rims starting at the edge of a shelf, leaning against kiln wall but not touching an element, I think it was 3 or4 platters at a time. I've also tried propping them against a larger pot on the shelf, slight cupping that way also.  ^04. Can I ask how you do it?

[Mark C.]

Benzine

The spoonrests donot stack well- they puch on each others lips-several times ai have loaded them vey wet-just dry enough to handle . So when stacked the curved up as they dried in kiln.

 

Min

I first cooked then bone dry in heated shop-I mean real dry and hot to the touch. None of this cold cheek stuff.I often cook the shop in late fall and winter to get the pots dry with my natural gas heater-top of shop runs in the upper 90's. Then stacked against wall of kiln about middle top of kiln . The other side had stacked 1/2 shelves

I fire most of my bisque in gas 35cb car kiln (average 33 bisques a year)I do about 5 in larger electric-usually last minute catch up loads or add on so I can fire all the kilns in a glaze fire at same time.Most platters are fire in gas kiln most of the time.

I have had success with this but its been a few years. That body was Daves Porcelain with white fine grog.

The platters where almost straight up with other pots stuffed next to them.

Mark

[Min]

 

 

Min

I first cooked then bone dry in heated shop-I mean real dry and hot to the touch. None of this cold cheek stuff.I often cook the shop in late fall and winter to get the pots dry with my natural gas heater-top of shop runs in the upper 90's. Then stacked against wall of kiln about middle top of kiln . The other side had stacked 1/2 shelves

I fire most of my bisque in gas 35cb car kiln (average 33 bisques a year)I do about 5 in larger electric-usually last minute catch up loads or add on so I can fire all the kilns in a glaze fire at same time.Most platters are fire in gas kiln most of the time.

I have had success with this but its been a few years. That body was Daves Porcelain with white fine grog.

The platters where almost straight up with other pots stuffed next to them.

Mark

 

Thanks Mark. So maybe I had problems firing on edge because of the clay? I think I was using Glacier porcelain (from Tacoma Clayart) at the time, no grog. They would have been dry going into the firing, I candle a few hours if in doubt.

Min

[Mark C.]

I used to have trouble with large flat forms made from Dave's . Another potter and I split a ton of this white fine groged Dave's many years ago. Its now long gone and I'm back to my 10 tons of regular Daves a year and have not seen any cracking with large forms in years.

I make large bowls and a few platters with it. The big stuff has slowed down in terms of sales past years and just recently is picking back up.

I'm off to Anacortes Wa. Art show mostly with van full of small stuff this week.

For flat large pressed forms I use 1/2 and 1/2 thats a Laguna body-1/2 Daves and 1/2 WSO. That stuff is bullet proof.They make it grog or sand and the sand has cracked some so I only use the groged on large press mold works.

Anything less than 12x12 I use straight Dave's on as well as all thrown production. I have used Dave's since middle 80's before Laguna Clay bought out Westwood Ceramics. Its only gone bad on me once in a major way and they never fested up but I did get my pound of flesh from the owner.

It was quite a story and I'm told they still recall it at the plant Jon Pacini later told me.

Mark

[Marcia Selsor]

Mark, I don't lean anything flat against the kiln wall and element. I make a structure of bricks in the center of the kiln.

In my big oval, i can make several structures.I stack several large slabs 22-28" against them. Both sides of the structure. I think stacking against the wall would catch the radiant heat from one direction and cause the warping. I also raise the slabs on the coils. I am a big believer in those. You wouldn't have that need with the tangent of a platter.

For large columns I have found that it is very important to use the coils or raise the piece off a solid structure to let the bottom dry. I can't flip these once that are decorated. During the firing air /steam can blow out the bottom if the piece is not completely dry. Have you ever seen holes in the feet of large antique platters or serving dishes? This is to allow heat circulation and let out steam.Since I add large coils at the bottom of the columns, they need to have a way to shrink in the firing and to allow heat to circulate. It is a simple thing and it works.I don't get any cracking or warping doing this. For an 8" diameter column, I put little coils about every inch in a radiating pattern.

Marcia

[Isculpt]

Wow, what a lot of good information.  I will definitely incorporate Marcia's coils.....

[Benzine]

Wow, what a lot of good information.  I will definitely incorporate Marcia's coils.....

Good information indeed.  Though, I may have to start avoiding these forums, I'm on my break for the summer, I'm not supposed to be learning new things....

[Marcia Selsor]

Benzine,

In ceramics I try to learn something new every day...there is way too much to learn."so little time" No summer vacation for you!!!

Marcia

[Idaho Potter]

Jayne, you used to do figurative sculptures, and if you still are, firing the irregular shape sculpture on its side could cause additional stress to the bases and set everything askew.  Unless you could keep the sculpture and the base on an even level, I think warping is a definite possibility. 

 

Most of the discussion here has been about plates and platters.  Unless your recent work resembles those items, I don't see how it pertains to sculpture.  Seeing as it is a bisque firing, you can arrange your sculptures close enough to touch.  I think if a sculpture is created in an upright position on a base and, is intended to be in that same position when finished, that is how it should be fired.

 

Shirley

[Isculpt]

Shirley, I didn't find your post until now.  Thanks for the insights.  As a sculptor, you certainly understand the challenges I'm facing.  I have to admit that I was afraid that placing a tall piece on its side would have unhappy results, but I was hoping to hear that I was just being a worrywart.  I'm currently limited by the size of my kiln -- 18"x18", but I've ordered a much larger one that is 29" high, 35" long, and 25" deep -- and ALREADY I'm trying to figure out how to fire work that's taller than the new kiln!!!!! 

 

Jayne

[Idaho Potter]

When I end up with something that's going to stress me out because it may bump its head on the lid, I try to find someplace on the piece that would work as a seam.  I then cut through that line  so the two pieces can be fired separately, even if you have to create a "cradle" to fire things that aren't flat bottomed.  If it is a figure--clothed--try to make the cut line around the waist.  For example, a waistband, belt or a top (shirt, blouse) that will hang over the waistband.  Look at the piece as if it were a teapot and the bottom area will have a gallery, and the top will fit into or onto like a lid.

 

Does this make sense?

 

Shirley

[Mark C.]

I expect zero warping in a bisque firing. Thats what you will get if the work is dry.

Even if work is on side or piled high or one piece per load.

Mark

[OffCenter]

I expect zero warping in a bisque firing. Thats what you will get if the work is dry.

Even if work is on side or piled high or one piece per load.

Mark

 

Even if the work is not dry it will not warp... it will explode instead.

 

Jim