Abstract: The core box vent useful in core making, comprises a porous cylinder of sintered ceramic materials, the pores of such cylinder being less than will allow intrusion of the grain size of sand to be introduced to the core box. A method of making cores using the above vent comprises, first, providing mateable core box sections with blow tubes permitting introduction of an air fluidized sand mixture into the interior of such box sections and providing one or more ceramic core box vents in an exhaust side of the mating core box sections to permit egress of air used to fluidize the sand mixture the vents have a labyrinth of passages or pores smaller in diameter at least than the average grain size of the sand in the mixture sand and resin mixture is blown into the interior of the mated core box sections, with the resin being curable to polyurethane by chemical reaction. Next a catalyst curing gas is blown through the mixture via such blow tubes. Lastly, the mixture is purged with air.