Abstract: A process is provided for removing slag from an aperture in a substrate, comprising the steps of: providing a protective coating on the substrate; drilling a hole through the substrate; and chemically removing slag from the aperture by complete or partial immersion of the substrate into a chemical bath. Additional process steps can include cleaning the stripped substrate and baking the substrate at a high temperature. A base coating can be provided on the substrate to promote adhesion of a chemically resistant coating to the substrate. Additionally, a protective coating can be applied to the chemically resistant coating to protect it during drilling. The chemically resistant layer can be a material, such as gold, that does not oxidize or dissolve when it is exposed to a chemical, such as phosphoric acid. Phosphoric acid can be heated to accelerate slag removal.