To obtain various artistic effects, metals are sometimes coloured by dipping into different chemical solutions or by the combined action of air and heat to form tinted oxides, or by the application of coloured lacquers. Lacquers are practically varnishes, and when properly applied, preserve the surface of the metal from being acted upon by an inside atmosphere for a considerable length of time. In japanning or enamelling, the work is stoved in a suitable oven after the application of the enamel, to give it the necessary hardness. Lacquering and other solutions for every possible purpose can now be so cheaply obtained that it is not worth while attempting to make them up. White or other enamelled utensils, for culinary use, have their surfaces treated with a vitreous matter, afterwards being baked in an oven 01 furnace.