To destructively remove a casting core from a cast part, the part is exposed to a combination of nitric acid and sulfuric acid. The combination may have, by volume, a nitric acid concentration of 4-20 times the sulfuric acid concentration. The combination may be an aqueous solution including, by volume, 40-60% nitric acid and 3-10% sulfuric acid. The method may remove a ceramic casting core and a refractory metal-based casting core. A first leaching step may remove a major portion of the ceramic casting core and may comprise alkaline leaching. A second leaching step may remove a major portion of the refractory metal-based casting core and may comprise acid leaching. The acid leaching may comprise the combination of nitric acid and sulfuric acid.