Summary The application of a type of porous ceramic coating, typically 80 to 400 microns thick to metal, is described. These coatings were developed for mild steel self-clean oven liners to assist removal of fat splatters during cooking operations at normal oven temperatures. The coatings are based upon specially developed “self-matting” vitreous enamels, which, unlike conventional ones, show controllable fusion characteristics during firing in the temperature range 750-850°C. Thus high porosity, hardness, and good adhesion can be achieved simultaneously. Catalysts or catalyst support material can be incorporated in the coatings before firing as with oven liner catalyst or preferably after firing by eg an impregnation step. Uses of the coatings or coating materials for reactions other than fat removal are possible. Coatings can be made having a wide range of pore size distributions and their surface areas can be up to over 100 m2/gm.