In the present invention there is provided a method for producing a self-supporting ceramic or ceramic composite body by the oxidation of a parent metal to form a polycrystalline ceramic material comprising the oxidation reaction product of said parent metal with an oxidant, including a vaporphase oxidant, and optionally one or more metallic constituents dispersed throughout the polylcrystalline ceramic material. The method comprises the steps of providing at least a portion of said parent metal for establishing at least one surface of the ceramic body, and heating said parent metal to a temperature above its melting point but below the melting point of the oxidation reaction product to form a body of molten metal. At that temperature, the molten metal is reacted with the oxidant, thus forming the oxidation reaction product. At least a portion of the oxidation reaction product is maintained in contact with and between the molten metal and oxidant to transport the molten metal through the oxidation reaction product toward the barrier means and into contact with the oxidant so that fresh oxidation reaction product continues to form at an interface between the oxidant and previously formed oxidation reaction product. The reaction is continued until the oxidation reaction product contacts the barrier means to produce a ceramic body having the surface established by the barrier means. A shaped ceramic composite is formed by superimposing a barrier means onto either a loose mass of filler material or a self-supporting preform, and infiltrating the mass of filler or preform with the polycrystalline ceramic matrix, which grows until it contacts the barrier means.