Warping is when a pot bends out of its intended shape, such as a round rim going oval or a plate dishing down, during drying or firing. It usually comes from uneven drying, uneven walls, overfiring or poor support in the kiln.
What Is Warping?
In drying, warping happens when one side loses water faster than the other, such as a plate drying from the top while the base stays wet, or a pot near a heater. Clay also has a kind of memory: a rim knocked out of round when soft may look fixed, then return to the distortion in the kiln.
In firing, Digitalfire points to overfiring as a common cause, often because a kiln controller takes the clay hotter than assumed. Porcelain warps most, because it contains more feldspar and is fired close to its melting point. Uneven wall thickness and pieces close to elements make it worse.
Prevention includes drying slowly and evenly, drying flat pieces under light weight or on a wire rack, keeping walls even, and firing to the clay’s rated cone, checked with witness cones.
Wide plates and platters sometimes need a thicker foot ring or extra support in the kiln, and lids are often fired in place so they warp together with their pots.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.