The qualities generally designated smalts are those deposited in the third and fourth vessels; they are also known as king’s blue or azure blue. The processes used in different works apparently vary. The essentials of the processes are, however, as they have just been described; the time during which the liquid is left in the various depositing vessels is different. Smalts, being a glass, well resists the action of the weather, although on account of the absence of lime it has not the great chemical indifference of ordinary glass. Smalts is not altered by atmospheric influences, but from analogy with the behaviour of water-glass, to which smalts is closely related in chemical composition, we should conclude that, although smalts resists the action of the air for a tolerably long time, it cannot be regarded as absolutely permanent; in the course of time potassium carbonate and silica will be formed. Since the introduction of the manufacture of ultramarine, the use of smalts has considerably decreased. Ultramarine is incomparably the more handsome pigment, but it cannot be exposed to high temperatures without undergoing change of shade. For purposes in which the pigment is subjected to a high temperature, as in porcelain painting or earthware glazing, smalts has maintained its position. Smalts is also used in fresco painting, for colouring wax and tinting writing paper. For the latter purpose it should be rejected. It has no influence on the durability of the paper, but it spoils steel pens. Any one who has written for a long time on paper coloured with smalts must have observed this; the best steel pens are soon worn out by such paper. The very fine splinters of glass present in large number in the paper act upon the steel as a very fine but very hard file, and quickly wear it down. When smalts are used for painting earthenware, the outlines of the design are quite obliterated, the cause of which is that smalts, being itself a glass, fuses with the glaze (also a glass) of the vessel. When clean outlines are required smalts should not be used; some other cobalt pigment resisting heat should be substituted. In addition to the above blue pigments which are in common use, there are two others to be mentioned, rarely used and very costly—tungsten blue and molybdenum blue. =Tungsten Blue= is made by adding excess of ammonium chloride solution to a hot solution of potassium tungstate, collecting the precipitate resulting when the liquid has completely cooled, drying and heating to redness in a crucible, through the cover of which a porcelain tube reaches to the bottom. When the crucible begins to glow, hydrogen is passed through the tube; the crucible is then heated to a full red heat for fifteen minutes, the current of hydrogen being continued. The pigment obtained in this way is a deep blue powder of velvety appearance.