The disclosure relates to investment casting. More particularly, the disclosure relates to the removal of wax patterns from casting shells. One aspect of the disclosure involves a method for removing a carboncontaining

pattern material from a casting shell. The pattern material consists essentially of wax. The shell contains a casting core. The casting core is a ceramic casting core. The method is used to manufacture a gas turbine engine component. The method comprises a first heating and a second heating after the first heating. The first heating has a lower minimum pressure than the second heating. It is at a minimum pressure of less than 1.3 Pa. The first heating is at a lower median oxygen partial pressure than a median oxygen partial pressure of the second heating. The first heating peak temperature is at least 816 °C. The first heating peak temperature is 816 °C to 1,093 °C and the second heating peak temperature is 649 °C to 982 °C. The first heating peak is in a first furnace and the second heating is in a second furnace, different from the first furnace. The casting method includes the method for removing the carbon-containing pattern material. The method further comprises: molding the pattern material over a casting core to form a pattern; forming the shell over the pattern; after the removing, casting a metallic material in the shell around the casting core; and destructively removing the shell and casting core to leave a cast part. The cast part consists essentially of a nickel-based superalloy. Another aspect of the disclosure involves a method for removing a carbon-containing pattern material from a casting shell. The method comprises a first step for evaporating and pyrolizing the pattern material to leave carbon and a second step, for oxidizing the carbon. The first step includes applying vacuum. The second step includes introducing oxygen. The first step comprises exposing the shell to a pressure of less than 1.3 Pa while at a temperature of at least 816 °C. The second step comprises exposing the shell to an oxygen partial pressure of at least 10kPa while at a temperature of at least 649 °C.