A hollow metal article can be fabricated by casting a molten metal alloy around a core, solidifying the molten metal alloy to form a metal article, and chemically removing the core from the metal article to form a hollow cavity in the metal article. The core includes a ceramic core body and an x-ray radiopaque coating disposed on the ceramic core body. A method for testing the hollow metal article includes submitting the hollow metal article to x-ray imaging and determining based upon the x-ray imaging whether any of the x-ray radiopaque coating of the core remains in the hollow metal article.