A method of forming at least one concavity of a selected size and shape within a surface of an internal passageway of a metallic component comprises: depositing a ceramic-based material by a direct-write technique onto a ceramic core which is suitable for forming the internal passageway during a casting process to form the metallic component, wherein the ceramic-based material is deposited as a positive feature; heat-treating the deposited ceramic-based material; forming the metallic component by a casting process in which the ceramic core is incorporated into the casting, in a position selected as a desired position for the internal passageway; and then removing the ceramic core from the metal component after the casting process is complete, thereby forming the internal passageway, with the concavity contained within the surface of the passageway, said concavity formed by removal of the positive feature of the ceramic-based material.