A.--_Photo-engraving of Line-work._--A plate of copper is prepared by covering it, either by flowing or with a roller, with a very thin coating of a solution of: Sugar 2 grammes. Bichromate of ammonia 1 gramme. Water 14 grammes. This coating is equalized and quickly dried by means of an arrangement which keeps it in rotation over a warm plate. As soon as the plate is dry, a positive cliche of the drawing to be reproduced is laid upon it, and the whole exposed to the sun for a minute, or to the electric light for three minutes. The reaction produced is the same as with the citrate of iron, but much quicker; the exposed parts are no longer hygroscopic, but in the parts protected by the lines of the drawing the sensitive coating has retained its stickiness, and will hold any powder that may be passed over it, thus producing a very clear image of the drawing. The coating being excessively thin, the little moisture it holds and the powder applied suffice to break its continuity, especially if the powder be slightly alkaline. If the rest of the surface were sufficiently resisting, the plate might be bitten at once; but light alone is not enough to produce complete impermeability: the action of heat must be combined with it. The plate is, therefore, placed on a grating, with wide openings, a large flame is applied underneath, and it is heated till the borders where the copper is bare show iridescent colors. The sugary coating thus becomes very hard in the exposed parts, but under the powder it is broken, porous, and permeable to acids. The surface is then covered with the biting fluid, which is a solution of perchloride of iron at 45 deg. Baume, and after few minutes' contact the plate is engraved. It only remains to clear off the bichromated sugary coating which forms the reserve, and which, being hardened by the heat, resists ordinary washing. It is removed perfectly by rubbing the surface with a hard brush and warm potash lye; the plate is then ready for printing. Sometimes it may be necessary to give several successive bitings, or to use a resinous grain; in such cases the various methods of the engraver's art are employed. B.--_Photo Engraving for Half-Tones._--To reproduce by engraving the image of any object, a portrait, or a landscape, the gradation of tint is obtained by repeating three times in the following manner the operation A, just described: The copper plate being prepared as before, it is exposed to the light under a positive, and given a long exposure, say four minutes, in the electric light. The sugary coating hardens under the whites and the lighter shades--it only remains tacky under the blacks. The positive cliche is removed, the plate powdered, and bitten; the blacks alone come out.