Enamelling of Metals

Vitreous enamel coatings are fundamentally films of glass specified along with inorganic pigments. Such coatings contain the best chemical resistance and inertness of glass.

Enamelling is prepared by glass former (SiO₂ + borax), stabilizer (CeO and Al2O3), opaque agents (TiO₂ and ZrO₂) ,flux (potassium and sodium oxides),  and coloured pigments. All of those chemicals are smelted together at 1200 to 1300^oC, and the molten mass is ground in cooled and pebble in water. After that, this product is ultimately milled in ball mills along with clay, water and sodium silicate to a fine slurry and is sieved. Then this is applied by dipping or spraying on cleaned objects. The coating is first dried at a temperature of around 125^oC, and then burnt at 500 to 800^oC for 4 to 10 minutes, based upon the kind and thickness of the base metal. The enamel, that is partly molten in this procedure, is strongly bonded to the base metal and makes a shining surface.

Vitreous enamel contains good corrosion resistance towards alkali, acids (except hydrofluoric acid), boiling water and several organic solvents. It contains also pleasing colours, electrical properties, permanence in form, and good resistance to wear. Though, high brittleness limits its use.