A mold (1) for cast-molding a slip is provided, which comprises a divsible casting mold including a plurality of mold portions to form a mold cavity (4) when mated together; each mold portion including an air-tight housing (2), an intermediate layer (5) of coarsely porous structure adjacent to the air-tight housing (2), and a solid synthetic resin filter layer (3) of fine open-cell structure; a slip supply duct (8) being connected with said mold cavity (4) and communicated with the outside of the air-tight housing (2); a fluid-flowing duct (9) being connected with said coarse intermediate layer (5) and communicated with the outside of the air-tight housing (2); said filter layer (3) being permeably joined to the coarse intermediate layer (5), and having substantially precise shape and dimension of substantially uniform fine open-cell structure. Such a filter layer (3) is produced by molding a flowable emulsion material comprising by weight about 100 parts of a curable synthetic resin material, about 1 to about 30 parts of a non-ionic emulsifier, about 1 to about 200 parts of water, and about 50 to about 600 parts of filler particles, into a cured filter layer; and uniformly eluting with a solvent an emulsifier-based viscous substance finely dispersed in the cured resin layer, and further curing the resin layer.