To provide a protecting coating of an oxidizable investment casting core.

A substrate (50) is coated by applying a first layer (52) containing a non-heat resistant first metal in major weight part on the substrate (50). A second layer (54) containing a second metal carbide and/or nitride in major wight part, is coated on the first layer (52). A third layer (56) containing a ceramic in major weight part, is coated on the second layer (54). The substrate (50) can be made to be a heat resistant metal based investment casting core (38).