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If ye're trying to simulate a brick oven, why not make that thing entirely out of terra cotta? It might be a little dicey to get a large clay slab (easily made on a slab roller or with a large rolling pin set over two guide rails, however) to dry uniformly without cracking or warping, but I suspect it could be done if the ware were allowed to dry slowly, loosely wrapped in plastic or whatever. You could also carve nice designs in it. Slip casting in a plaster mold could be used if'n all y'all wanted to go into mass production. Dinnae forget that between modeling and firing, you are talking something like 13% shrinkage in size due to water loss from the clay.