A Manual Of Photography

DAGUERRE’S IMPROVED MANIPULATION. 239 “This process consists in covering the plate, after having polished it, with a layer of very pure water, and heating it very strongly with a spirit-lamp, and in afterwards pouring off this layer of water in such a manner that its upper part, where the dust which it has raised floats, does not touch the plate. “ It is necessary to have a frame of iron wire of the size of the plate, having at one ot its angles a handle, and in the mid- dle, on the two opposite sides, two small cramp-irons, to retain the plate when it is inclined. After having placed this frame on a horizontal plane, the plate is placed on it, which is covered with a layer of very pure water, and putting as much water as the surface can retain. The bottom of the plate is afterwards very strongly heated, and very small bubbles are formed at the surface. By degrees these bubbles become larger, and finally disappear ; the heat must be continued to ebullition, and titen the water must be poured off. The operator should commence by placing the lamp under the angle of the frame where the handle is ; but, before removing the frame, this angle must be very powerfully heated, and then, by gradually removing it by means of the handle, the water immediately begins to run off. It must be done in such a way that the lamp shall follow, under the plate, the sheet of water in its progress, and it must be only gradually inclined, and just sufficient for the layer of water, in retiring, not to lose in thickness; for, if the water were dried up, there would remain small isolated drops, which, not being able to flow off, would leave on the silver the dust which they contain. After that, the plate must not be rubbed: very pure water does not destroy its polish. < Tins operation should be performed only just before iodising the plate. AVhilst it is yet warm, it is placed in the iodising box, and, without allowing it to cool, it is submitted to the vapour of the accelerating substances. Plates thus prepared may be kept one or two days (although the sensibility diminishes a little), provided that several plates be placed opposite to one another, at a very short distance apart, and carefully enveloped to prevent change of air between the plates. “The plates cannot be too well polished. It is one of the most important points to obtain a fine polish ; but the purity often disappears when substances which adhere to the surface of the silver are used,—such as the peroxide of iron, which has keen very generally made use of for giving the last polish. TItis substance, indeed, seems to burnish the silver, and to "Ive it a more perfect polish ; but this polish is factitious, since it does not really exist on the silver, but in fact on a very fine layer of oxide of iron. It is for this reason that there is re-