Abstract: A method of applying an enamel coating (14 and 15) to an apertured (11) metal base (10) is characterized by plugging the or each aperture with an electrically insulating material (12), applying a coating (14, 15) of a vitreous material to one or both surfaces (13 and 16) of the base and then removing a core (18) of the vitreous material and the insulating material from the or each apertures to leave it lined with insulating material during subsequent firing of the vitreous material.By this means, thinning of vitreous material around the aperture is avoided, reducing the likelihood of electrical connection between the metal base and an electrical conductor extending through the aperture. The invention has particular application to the manufacture of electrical printed circuits.