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Stoneware and porcelain plates having overhung rims and wide flat bases are extremely difficult to keep flat (as this potter discovered). In industry they are fired in setters, or even rim down, to temperature, then glazed and fired lower. As a potter, the best you can likely do is pay attention to the cross section shape (not too flared, inherently strong), fire on flat shelves, minimize changing shape on handling when soft or leather hard, dry evenly, avoid a sharp concave outer contour between foot and wall (bevel it well) and keep the center portion thick enough so it does not pull upward as the rims slump (especially if rims are thick). Working at low temperature can be a solution, but terra cotta clays are generally not stable for this shape if fired past cone 04. White burning low fire bodies are better but also more porous, so glazes must fit well to avoid crazing.
Troubles |
Warping
There are multiple reasons why pottery and porcelain pieces can warp during firing, both vitreous and non-vitreous ware. Here is what to do about it. |
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