Abstract: A casting mold is disclosed for preventing growth of parasitic grains in the casting of a workpiece from a liquid metal by a single crystal solidification technique. The mold has a mold portion which defines a casting cavity in the shape of the desired workpiece as well as a feeder portion which defines a separate feeder cavity not in communication with the casting cavity. The feeder portion is in heat exchange contact with the mold and is located adjacent to the areas of the workpiece in which a parasitic grain may be nucleated during the controlled solidification. The feeder portion is filled with a thermal mass which emits heat to slow the liquid metal solidification in these zones in order to prevent a growth of the parasitic grain. The thermal mass in the feeder cavity may consist of a liquid metal which undergoes a phase change at the same temperature, or a slightly higher temperature than that of the liquid metal located in the casting cavity from which the workpiece is cast.