In regard to the colour itself, experiments have shown that the most beautiful green is that formed by igniting the manganate as described above. The green prepared by Rosenstiehl’s process--fusing together caustic baryta, chlorate of potash, and binoxide of manganese--is less beautiful than the above; while that attained from nitrate of baryta and binoxide of manganese is far inferior to either of the others. Perhaps, however, this colour could be improved by preparing it in a reverberatory furnace with a strong oxidising flame. The blue-green baryta pigment has different shades, according to its preparation, some being almost pure blue with only a shade of green, and resembling the light blue quill feathers of many parrots. The greener the colour the more it gains in intensity, but it loses in fineness, although still surpassing the green manganate of baryta. The production of the blue or bluish-green baryta is due entirely to the alkaline property of the mass. Whether each definite colour is due to a definite composition is doubtful, since the temperature, which must not exceed that of a bright red heat, exerts a greater influence on the colour. This much is however certain, that both manganic acid as well as the permanganate of baryta, when mixed with about 20 per cent. of hydrate of baryta and ignited at a red heat, will always produce this blue-green colour. It is evident that the blue-green colour is dependent entirely on its basic character; for on placing this powder in weak acids, it first turns green and is then gradually decomposed. The baryta pigment is quite permanent, and may be subjected to the action of strong sulphuric acid for hours, at the ordinary temperature, before the colour will be destroyed. Boiling potash solution has no perceptible effect upon it. The permanence, especially of the blue shade, is increased by adding a little baryta, which increases its alkalinity. It is also worthy of remark that the pigment prepared from the nitrate of baryta is much less permanent, because the nitrous acid present will after a time exert a reducing action. The baryta pigments seem especially adapted to fresco painting, because they appear very bright and lively on stone, and especially on lime, where many other pigments lose their beauty or are entirely destroyed. BREMEN GREEN.--This old-fashioned pigment is a basic carbonate of copper, and has been produced in several ways. At first a basic chloride or oxychloride was used, its mode of preparation varying somewhat but without affecting the character of the result, the great essential being that no subchloride of copper should be present. Therefore, in some factories, it was the practice to prepare the magma of basic oxychloride even a year in advance; or, to subject it to repeated wetting and drying in order to ensure prefect oxidation. The method has now become obsolete, and is superseded by the following:--