Bryan D

Thank you all for your help. I’ve tried 5, 10, and 17% EPK. 10% seems to have corrected most of the warping issue. 5% was not enough. I’m currently bisquing a larger run of 40 mugs and should know definitively by the end of the week if 10% EPK is the solution. Although now I think I have a bit of a glaze fitment issue and it seems like EPK is causing more pinholes even in heavily deflocculated slip (more testing soon). Jeff – thanks for the suggestion. You found trimming the lip outside of the mold resulted in less deformed? The shear force from the razor didn’t cause deformation? Did you trim with the cone in place and what was the cone made of (plaster?)? Does deformation only happen when the clay is wet? Could a wet sponge on the lip of a bone-dry piece cause warping in the kiln? Would there be a difference between (wet) sponging the lip and using a fettling knife (dry)? It took me a few months, but I’ve learned to reach into the mold and lift the piece up by applying outward pressure near the bottom rather than flipping the mold upside down. I can get the body of the mug into the bisque almost completely circular. I’ve seen others leave a conical piece from the casting on their mugs and then cut it off when it’s bone dry. I’d prefer not to add this extra step, but will consider once I’ve exhausted other options.

Mark and Liam - thank you! I'll try both 5% and 10% this week and post results. I'm using a cone 5 body.

Hi all, My slip cast porcelain mugs are warping. The clay body is purchased dry from Laguna clay and I mix to 1.8 SG with their recommended deflocculates. I've been trying to troubleshoot this issue for 4 months. I've even left the body of the mug in the mold until bone dry and then placed directly in the kiln without attaching a handle or cleaning the rim - it still warped. Here are some other things I've already tried: Drying slowly and evenly over a week Carefully removing from mold such that they are still circular before bisque Casting thicker walls Compressing the clay with a sponge and rib on a wheel while still in the mold Tracking placement in the kiln Anyone else have other recommendations? If I used a stoneware slip would that solve the problem? Warping always happens in the glaze kiln, not in bisque. It is not always warped in the same direction (ie. not always slumped from the weight of the handle). I know porcelain is notorious for warping and the shape of my mug isn't helping, but I figure there must still be a way. 1 out of 10 come out circular. 9 out of 10 look like the photo. Thanks for the help!