Hitherto confined to painting and engraving, lamp black has lately refuted the assertion that there is nothing new under the sun by making its appearance in photography. By a method which combines the fidelity of that art with the permanence of prints, there is produced a species of photographic engraving, so to speak, having lamp black or carbon for its colouring matter. Indeed, in this 'Autotype' process, as it is called, any other durable pigment or pigments may be used, and a photographic picture thus obtained. In copying the works of artists, especially, the mode promises to be of value, inasmuch as by its agency the same pigments may be made the colouring matter of the reproduction as are employed in the original. If this be in sepia or bistre, the copy can be autotyped in those colours; or if a red chalk drawing be required to be multiplied, the proofs may be in red chalk, the copy when produced to the same scale being scarcely distinguishable from the original. In like manner, any single colour of the artist's palette is applicable without restriction or limitation, so that not only are every line and touch rendered absolutely, but the very pigment used in the original is found in the copy. Moreover, as the pigments are quite unchanged by the action of the other agents employed, the resulting colour of the print is determined once for all, just as the artist mixes those pigments on his palette for his picture. As extending the use of lamp black and permanent pigments in general, this brief digression on Autotypography may be pardoned in a treatise on colours. 295. MIXED BLACK. Black is to be considered as a synthesis of the three primary colours, the three secondaries, or the three tertiaries, or of all these together; and, consequently, also of the three semi-neutrals, and may thus be composed of due proportions of either tribe or triad. All antagonistic colours, or contrasts, likewise afford the neutral black by composition; but in all the modes of producing black by compounding colours, blue is to be regarded as its archeus or predominating colour, and yellow as subordinate to red, in the proportions, when their hues are true, of eight blue, five red, and three yellow. It is owing to this predominance of blue in the constitution of black, that it contributes by mixture to the pureness of hue in white colours, which usually incline to warmth, and that it produces the cool effect of blueness in glazing and tints, or however otherwise diluted or dilated. It accords with the principle here inculcated that in glass-founding the oxide of manganese, which gives the _red_ hue, and that of cobalt, which furnishes the _blue_, are added to brown or _yellow_ frit, to obtain a velvety black glass. Similarly the dyer proceeds to dye black upon a deep blue basis of indigo, with the ruddy colour of madder and the yellow of quercitron, &c.