How to prevent this from warping when glaze firing?

[Fusionous]

Hello all,

I slab rolled this sculpture with stoneware PB103 and it warped during cone 6 glaze firing. I have made the rest of the batch and remaking them is not an option as i have a deadline in 1 weeks time. 

How do i prevent this from warping at the sides? Both sides should be flat and touching the surface.

 

Edited December 9, 2022 by Fusionous
Added in more info

[Mark C.]

If its NOT glazed fire another piece of  slab over the top keeping a slight pressure on it..But not enough to flatten the humps

Also clay has memory so how you form this is very important .Over bending or overworking can make it act like this as well.

If its glazed on one side only this will pull it up as well

 

One thing I do know is the more you NEED it and the less time you have the more it will act up so make 3 or 4  of them and mix it up fire one say on its side the other with a slab on top as noted

squeeze one with bricks on its side

Edited December 9, 2022 by Mark C.

[Fusionous]

I am glaze firing, is there anyway i can put something on top of it to prevent it from warping?

 

It is glazed on both side except the straight edge its supposed to be standing on somehow sagged down the middle.

What is iot?

Edited December 9, 2022 by Fusionous
Added in more info

[Mark C.]

its was my quick typing without proof reading

I fixed itnow

If its glazed then you cannot put anything on top

glaze the whole piece except where it touches the kiln shelf

can you tell us if its only  glazed on the top side??as that will pull it up or down 

[Fusionous]

It is glazed on both sides, placed as shown in the picture into the kiln. After firing, both sides warped and lifted up and sagged in the middle, causing the glazed part to touch the kiln shelf

[kswan]

There's way too much weight in the middle of that piece to be supported by those ends. If you can leave a part unglazed in the very middle, you can support it from underneath. For example, take a small shelf post and top it with a rolled or rounded piece of clay in the same shape as your curve. Since the sculpture will shrink you could make the support a half centimeter or so lower than your sculpture, which would still support it when it wants to warp downward.

[KachemakKaren]

I have a thought...

If your design structure holds its shape through a bisque firing, what about trying a low fire glaze  instead of cone 6? I have fired many sculptural pieces (which don't need to be fully vitrified) made of cone 6 clay to bisque temperature and finished with various paints and waxes rather than glaze.  I'm wondering if low firing might work for you.

[Fusionous]

8 minutes ago, KachemakKaren said:

I have a thought...

If your design structure holds its shape through a bisque firing, what about trying a low fire glaze  instead of cone 6? I have fired many sculptural pieces (which don't need to be fully vitrified) made of cone 6 clay to bisque temperature and finished with various paints and waxes rather than glaze.  I'm wondering if low firing might work for you.

The client chose this glaze which is a cone 6 glaze... i could recalculate and test for lower temp but i just dont have time though...

[Pres]

The only solution I would have is to use 3 point pin setters upside down on the piece, then put a kiln post on top of that to force the piece down. This will leave setter marks, that can be ground and then polished out. Tough situation given your time frame. Firing on the side does not seem to be an option and it will probably not change the warping problem.

Good Luck... Really!

 

best,

Pres

[Callie Beller Diesel]

Is there room in your situation to allow for negotiation for more time on this deadline? If you’re dealing with a client, this could be your best option for delivering the quality of work you want to present. Clay is notoriously temperamental, and explaining that you think your client deserves the best possible work you can offer and that you’ll settle for nothing less for them may be a possibility. If this isn’t a culturally acceptable practice, feel free to disregard.

If what I’m reading is correct: you have more versions of this sculpture that have not been glaze fired yet, and you want to be able to prevent similar warping in the next ones. If that assumption is the correct one, I’d put a pin setter of some kind underneath the sculpture at the points where you know it will sag so that it’s supported. The small pinpoints that are left from the setter can be buffed out easily. If you don’t have a suitable pin setter, you can make one out of wads of clay and lengths of Kanthal wire (the same as your kiln elements). 

If I don’t have my assumptions correct and you need to try and repair this exact piece and you cannot obtain more time, the solution is maybe a bit more risky. You have to not only push the end pieces down, but the middle dips in the piece also have to be raised from the surface. In addition to what Pres recommended about weighing down the end pieces with setters in a re-fire, you also need to build supports to re-elevate the middle parts. This may result in the piece sitting the way you want it to, but the piece may have more irregularities in it.

[Min]

2 hours ago, kswan said:

There's way too much weight in the middle of that piece to be supported by those ends. If you can leave a part unglazed in the very middle, you can support it from underneath. For example, take a small shelf post and top it with a rolled or rounded piece of clay in the same shape as your curve. Since the sculpture will shrink you could make the support a half centimeter or so lower than your sculpture, which would still support it when it wants to warp downward.

+1

Fill the gap under the middle 2 downward dips then the ends won't be pulled up.

[grackle]

I like to throw slabs, and I was taught to throw the clay one way and then the other to minimize warping.  also taught to turn the slab 45 degrees in the slab roller to minimize the warp factor.  No that it always works, but it seems to help.  Have been making cactus sculptures, and they do not always stay as straight as I would like.

[neilestrick]

That form is going to sag no matter how it's made. You either need to fire it low enough that the clay doesn't soften up, so at least a few cones lower than its maturation point, or you need to support the middle dips. You could just do a couple of little dimes sized unglazed spots on the bottoms of the dips where you could put a bit of clay to support it in the firing. If it's the same clay as you made the piece with then it's going to shrink with the piece.

[Fusionous]

8 hours ago, Pres said:

The only solution I would have is to use 3 point pin setters upside down on the piece, then put a kiln post on top of that to force the piece down. This will leave setter marks, that can be ground and then polished out. Tough situation given your time frame. Firing on the side does not seem to be an option and it will probably not change the warping problem.

Good Luck... Really!

 

best,

Pres

I tried firing on the side, it warps and slants inwards instead, top narrow and bottom stays wide

[Fusionous]

8 hours ago, Pres said:

The only solution I would have is to use 3 point pin setters upside down on the piece, then put a kiln post on top of that to force the piece down. This will leave setter marks, that can be ground and then polished out. Tough situation given your time frame. Firing on the side does not seem to be an option and it will probably not change the warping problem.

Good Luck... Really!

 

best,

Pres

Haven't tried this yet, i have 2 more spares which i can experiment. Will update again with pins supporting the 2 valleys. Thank you so much!

[Fusionous]

7 hours ago, Callie Beller Diesel said:

Is there room in your situation to allow for negotiation for more time on this deadline? If you’re dealing with a client, this could be your best option for delivering the quality of work you want to present. Clay is notoriously temperamental, and explaining that you think your client deserves the best possible work you can offer and that you’ll settle for nothing less for them may be a possibility. If this isn’t a culturally acceptable practice, feel free to disregard.

If what I’m reading is correct: you have more versions of this sculpture that have not been glaze fired yet, and you want to be able to prevent similar warping in the next ones. If that assumption is the correct one, I’d put a pin setter of some kind underneath the sculpture at the points where you know it will sag so that it’s supported. The small pinpoints that are left from the setter can be buffed out easily. If you don’t have a suitable pin setter, you can make one out of wads of clay and lengths of Kanthal wire (the same as your kiln elements). 

If I don’t have my assumptions correct and you need to try and repair this exact piece and you cannot obtain more time, the solution is maybe a bit more risky. You have to not only push the end pieces down, but the middle dips in the piece also have to be raised from the surface. In addition to what Pres recommended about weighing down the end pieces with setters in a re-fire, you also need to build supports to re-elevate the middle parts. This may result in the piece sitting the way you want it to, but the piece may have more irregularities in it.

 

7 hours ago, Min said:

+1

Fill the gap under the middle 2 downward dips then the ends won't be pulled up.

I have a cookie with holes which i can place pins in, so i will need to support the 2 valleys correct? 

 

Are setters kiln props?

[Babs]

Orders for unknown forms need to be avoided imo.

Wondering why the need to be glazed underneath. 

I'd be checking low fired glazes as if you dont have time to redesign, you're risking complete failure to continue with C6. 

Supported with wrong height due to unk own shrinkage may well mean the ends move out, in . Hard to know, eh?

Not worth the angst and time you're wasting on this.

Good luck.

[Fusionous]

1 hour ago, Babs said:

Orders for unknown forms need to be avoided imo.

Wondering why the need to be glazed underneath. 

I'd be checking low fired glazes as if you dont have time to redesign, you're risking complete failure to continue with C6. 

Supported with wrong height due to unk own shrinkage may well mean the ends move out, in . Hard to know, eh?

Not worth the angst and time you're wasting on this.

Good luck.

Ok thanks, will definitely try to find replacements or alternatives...

Client wants to use it as a taco holder and chose this matte glaze i have.

Edited December 10, 2022 by Fusionous
Added info

[Babs]

Matt?, shiny ?, satin oatmeal?

What is that glaze

[Fusionous]

7 minutes ago, Babs said:

Matt?, shiny ?, satin oatmeal?

What is that glaze

Its a matte glaze. Meant to be a taco holder able to hold 3 orders on 1 side and 2 orders when flipped around...

[Mark C.]

Make it out of stainless steel-easy and it will not break

[Fusionous]

Just now, Mark C. said:

Make it out of stainless steel-easy and it will not break

Sadly client said stainless steel does not fit the restaurant theme...

[Callie Beller Diesel]

Kiln setters, pin setters or stilts are these thingy’s. This is an image of a commercially made 3 point setter, but they can come in different arrangements, like a long bar that has numerous points along its length. That’s what Pres was talking about with a bar setter. You can also make them very simply yourself with some Kanthal wire and a handful of clay. They’re used to place pieces on that are glazed all over, usually at low fire temperatures. The commercial ones come in 2 temperature ratings, one for low fire and one for mid fire. The wire in the low fire ones will bend if fired too hot, so if you’re buying them, make sure you have the right ones. If you’re making them, you have to use Kanthal, not Nicrhome wire.

[Jeff Longtin]

To expand on  Kswans point: my guess is that you took three round tubes and set them on a table and draped the clay slab over them? I would suggest you make three clay tubes the same diamter as the tubes you started with and fire the slab on them. Where the slab touches the clay tubes will need to remain unglazed, and the tubes would need to be kiln washed but this would give you the support you're missing.

I would close off the ends of the clay tubes to prevent them from collapsing as well.

[Fusionous]

8 hours ago, Callie Beller Diesel said:

Kiln setters, pin setters or stilts are these thingy’s. This is an image of a commercially made 3 point setter, but they can come in different arrangements, like a long bar that has numerous points along its length. That’s what Pres was talking about with a bar setter. You can also make them very simply yourself with some Kanthal wire and a handful of clay. They’re used to place pieces on that are glazed all over, usually at low fire temperatures. The commercial ones come in 2 temperature ratings, one for low fire and one for mid fire. The wire in the low fire ones will bend if fired too hot, so if you’re buying them, make sure you have the right ones. If you’re making them, you have to use Kanthal, not Nicrhome wire.

Yes i will be trying out this method. Probably 2 points per valley to support. thank you!