A Manual Of Photography

NATURALLY-COLOURED PHOTOGRAPHS. 173 have, at the same time, had a peculiar softness and brilliancy. Daguerre himself has remarked, that when he has been copying any red brick or painted building, the photograph has assumed a tint of that character. I have often observed the same thing in each variety of photographic material, i. s., where a salt of silver has been used. In the Philosophical Magazine for April 1840, will be found a paper,—" Experiments and Observations on Light which has permeated Coloured Media,”—in which I describe some curious results on some of those photographs which are prepared with the hydriodic salts exposed to luminous influence with coloured fluids superimposed; permitting, as distinctly isolated as possible, the permeation of the violet’and blue, the green, the yellow, and the red rays, under each of which a complementary colour was induced. During January of the present year, I prepared some papers with the bichromate of potash and a very weak solution of nitrate of silver : a piece of this paper was exposed behind four coloured glasses, which admitted the passage respectively of, 1st, the violet, indigo, and blue rays; 2nd, the blue, the green, and a portion of the yellow rays; 3rd, the geeen, yellow, and orange rays ; and, 4th, the orange and red rays. The weather being extremely foggy, the arrangement was unattended for two days, being allowed to lie upon a table opposite a window having a southern aspect. On examining it, it had, under the respective colours, become tinted of a blue, a green, and a red : beneath the yellow glass the change was uncertain, from the peculiar colour of the paper, and tins without a single gleam of sunshine. My numerous engage- ments have prevented my repeating the observations I desire on this salt, which has hitherto been considered absolutely insensible to light. Tire barytic salts have nearly all of them a peculiar calorific effect; the muriate, in particular, gives rise to some most rich and beautiful crimsons, particularly under the influence of li"ht which lias permeated the more delicate green leaves ; and also ’ in copying the more highly coloured flowers, a variety of tintings having been observed. We may always depend on producing photographic copy of a leaf of a green colour by the following arrangement:—Having silvered a copper plate, place it in a shallow vessel, and lay thereon the leaf of which a copy is desired, maintaining it in its position by means of a piece of glass ; pour upon it, so that the plate beneath the glass may be covered, a solution of the hydriodate of potash, containing a little free iodine : then expose the whole to sunshine. In about half an hour, one of the most beautiful photographic designs which can be conceived is produced, of a fine green yellow. The fluid