How to fix warped plates

[TBayCeramics]

I’m making slab plates and a few are coming out slightly warped. Is there a best way to sand or level these plates? Before bisque? After bisque or glaze firing? Thanks 

[Roberta12]

Are they warping while drying?  Or do you notice the warping after the bisque firing?

[Min]

Any warping that shows up in the greenware is only going to get worse in the glaze firing. Even if you did sand them the will likely still warp as the clay memory is still there.  I know it's hard to do but I think you would be better off if you scrapped the warped ones and made some more. Try and figure out why they warped though, did you lift the slabs without them being supported, roll in only one direction, uneven drying, too thin, too much overhang.......?

[neilestrick]

If they are made of porcelain, then may flatten out in the firing as the clay softens up.

[glazenerd]

Tbay:

as Min pointed out: porcelain clay can have a fair amount of memory.

if making large plates/ platters is your primary focus: then I would change porcelain. As a point of education: porcelain is specifically formulated to have high, medium, and low plasticity. The higher the plasticity, the higher degree of memory. I would be looking at tile body porcelain, as they are low plasticity/ memory. Others would have to make those recommendations, as I make my own clays.

porcelain can soften up at high temperatures, but typically highly translucent bodies are prone to deformation due to high feldspar content. Typical porcelain bodies tolerate heat well.

T

[Min]

Neil brings up a good point. If the bottom has a convex lift in the middle that can settle back down. @TBayCeramics, could you clarify where they are warping?  (it might help if you would post a picture) Also, what type of clay you are using?

 

[tinbucket]

If you use a slab roller and only roll the slab one direction, it can create uneven tension on the clay, and cause to shrink more in that direction. You may benefit by rolling the slab to the partial thickness, rotating the slab 90 degrees, then rolling to the finished thickness. You may also benefit from flipping the slab over. Another thing I have seen people do with slab plates is weigh them down while they are drying - a sand bag of sorts in the center of the plates. I think any combination of these techniques is worth trying. Some clays have a very sensitivd memory as others have mentioned and it is best to be aware of this when handling the clay - leatherhard pieces

[TBayCeramics]

Thank you all for your insights. I will definitely scrap the very warped greenware pieces but I’m wondering if there’s any way to slightly correct already fired pieces. With sandpaper? Or some other tool? Also, I’ve been double stacking them in my bisque firing, perhaps if I lay them flat in a single layer they will have less inclination to warp? Thanks again for your help.

[Mark C.]

They can be double stacked laying flat as long as the feet line up.I do that all the time on porcelain plates.

Are your plates thrown or slab built?

[TBayCeramics]

They’re slab built without feet.