[hinkley]

I feel like I've watched videos where people make Japanese and/or Korean ceramic cook pots and I can't for the life of me remember how they kept them from warping, just that they do.

The only trick I do remember is don't glaze the contact point between the two pieces. That not only adds thickness variability, but if glaze touches the bottom of the kiln you fuse to the bricks, so you have to elevate anything glazed, and elevating increases warping.