Keeping Plates And Slabs Flat

[Laurène Ashley]

Hello everyone, 

 

What are the secrets to keeping your plates and slabs flat??  I've been standing them up for the bisque firing, and some are still coming out warped.  Sometimes they correct themselves for the glaze firing, but it's always hit or miss.   

Thanks ! 

Laurène

[neilestrick]

Can you give us more info on what you're making, and how you're making them?

[fergusonjeff]

This is an issue I have been dealing with.  I make plates from slabs rolled out on a slab roller.  Here is a list of things I have done to reduce warping - most at the suggestion of a ceramics professor I pester relentlessly.

 

1) make them thicker.  My 8-10" plates are now about 1/4" thick

2) flip the slab while rolling.  I was rotating it, but flipping over will help more.

3) dry slowly.  I put the plates on drywall and cover loosely with plastic for a week or more

4) put some weight in the middle of the plate while drying.  I use reject mugs, but a better option would be a sock filled with sand.

5) add some fireclay and/or sand to the clay.  I do this using a pug mill, but it could be wedged in. I have been adding about 2# of each to about a 25# bag of commercial ^6 clay. Use the pure white silica sand you can get at most big hardware stores.

6) if you are making completely flat slabs then try drying between sheets of drywall. 

 

My understanding is that bisque firing on edge will reduce rather than increase the warping. 

[Roberta12]

I have been using porcelain for some square slab plates.  I do what fergusonjeff said with the flipping as you are rolling out slabs.  And I dry slowly with a bag of rice (lentils,pinto beans)  in the middle.  That does seem to help.  I still get some warping from time to time....never tried firing them on their edges!  I will now.

 

Roberta

[Laurène Ashley]

This is an issue I have been dealing with.  I make plates from slabs rolled out on a slab roller.  Here is a list of things I have done to reduce warping - most at the suggestion of a ceramics professor I pester relentlessly.

 

1) make them thicker.  My 8-10" plates are now about 1/4" thick

2) flip the slab while rolling.  I was rotating it, but flipping over will help more.

3) dry slowly.  I put the plates on drywall and cover loosely with plastic for a week or more

4) put some weight in the middle of the plate while drying.  I use reject mugs, but a better option would be a sock filled with sand.

5) add some fireclay and/or sand to the clay.  I do this using a pug mill, but it could be wedged in. I have been adding about 2# of each to about a 25# bag of commercial ^6 clay. Use the pure white silica sand you can get at most big hardware stores.

6) if you are making completely flat slabs then try drying between sheets of drywall. 

 

My understanding is that bisque firing on edge will reduce rather than increase the warping

Thanks for this.  I do 1, 3, 4 already.  I dry them on drywall, with a flat piece of wood on top.  I fire on edge as well for the bisque, but some things are coming out warped.  I does seem to be the thinner pieces though.  I try to roll everything around 1/4" inch.  Unfortunately I don't have a slab roller and have been rolling them out with a rolling pin and a wooden contraption that my dad made.  It definitely works the arms and abs!  

 

 

Can you give us more info on what you're making, and how you're making them?

 

My plates are coming out fine, but I've been making moon wall hangings, and some large round platters that have warped.  My moons might have been a little on the thin side, but my platter was rolled out to 1/4" and not only did it warp, but it cracked down the middle!   

[David Woodin]

Hello everyone, 

 

What are the secrets to keeping your plates and slabs flat??  I've been standing them up for the bisque firing, and some are still coming out warped.  Sometimes they correct themselves for the glaze firing, but it's always hit or miss.   

Thanks ! 

Laurène

Otto and Vivika Heino hammered the clay with a wood mallet down until close to the correct thickness than used the slab roller for the final thickness.  This helps to align the clay particles and works fine for me.

David

[Laurène Ashley]

Thanks David!  I'll try that!

[oldlady]

second that suggestion of pounding the slab.  i make "molds" from flat slabs.  have had cracking and warping often.  the last one is just finished drying and ready to fire.  it is flat, has been flat since the beginning.  i had very little clay left so i carefully made the shape i wanted and then pounded it with the thin side of a large, 1/4 inch thick yardstick.  whacking the sides with the thin side to square it up compressed the edges.   whacking it with the flat side on the top and bottom compressed the whole thing, rolling it with my 30 inch wide rolling pin over 1/4 inch sticks compressed it more. then i rolled leaves into the top with my pony roller.  it is still flat, no cracks.

 

let's see how it fires............