Abstract: Disclosed is a preformed ceramic base useful in firing an open-ended ceramic shell mold having a mold base prior to metal casting. The ceramic firing base includes a working surface having a majority of flat surface portions for supporting the mold base during firing and one or more groove-like surface portions which define gas circulation passages from the outside atmosphere into the open mold bottom when the mold base is placed in supported relation on the flat surface portions. The ceramic firing base thereby enables firing of a green shell mold while maintaining mold base flatness and circulation of furnace gas into the mold cavity to minimize mold hot spots. Also disclosed is a preformed ceramic firing cap to be used in conjunction with the ceramic firing base, the firing cap being adapted to cover the open top end of the shell mold to prevent foreign particulate from entering the mold.