A method of molding a ceramic vessel includes compressing a water-soluble powder, suspending the compressed powder shape in a mold, injecting a ceramic molding mixture into the mold, and dissolving the compressed powder by flushing the vessel with water. A core for making an arc discharge vessel that has a discharge chamber and two capillaries includes a molded core of the water-soluble powder having a shape of the discharge chamber, and preferably two capillary-forming pins extending from the molded core. An apparatus for removing the molded core that includes a water reservoir that preferably flushes water through the vessel and dissolves molded core.