Abstract: A process for treating waste foundry core and/or molding sand in a manner which upgrades these scrap streams to new sand quality for entry at the core making point. The process consists of incrementally heating the sand as required up to temperatures in the 1800.degree. to 2500.degree. F range, followed by cooling. The degree of heating is chosen to achieve a desired lowering of acid demand value (ADV) from that which would result from heating only to conventional high temperatures, about 1500.degree. F. Lowering of ADV reduces the variability which would otherwise be introduced into a mixture of new and recycled sand for cores.Heating waste molding sand to the temperatures contemplated by the method of this invention also causes clay additives to fuse, become non-absorptive and thus eliminating the need for mechanical attrition which would otherwise be needed to remove the clay so that it would not absorb high quantities of resin in the core making process.