A method and product made by using a polymeric ceramic precursor to synthesize dense, crack-free bulk ceramics in a technique using a sacrificial mold provides a ceramic structure for many technical, medical and industrial applications. The novel process uses an open cell material as a sacrificial mold to shape a ceramic precursor during curing. The cured ceramic green body can be machined and shaped to form the desired ceramic structure prior to final pyrolysis. The open cell material forms gas release paths to release large amount of gases generated during the pyrolysis of the cured ceramic precursor. After pyrolysis, an intact, dense, crack-free ceramic structure with high purity, strength and durability is obtained. Uses of the present invention include, but are not limited to, bulk ceramic parts, ceramic crucibles, a replacement material in some applications involving glass, silicon carbides, silicon nitrides, hafnium carbide and the like.