A Manual Of Photography

HELIOGBAPHY. THE PBOCESS OE M. NIEPCE. 17 it rings on being struck with the point of a knife, and flies off in pieces when separated from the dish. A small quantity of this material is afterwards to he dissolved in alcohol or ether; the solution formed should be transparent, and of a lemon-yellow colour. The clearer the solution, the more delicate will he the 1t must not, however, he too thin, because won d not thicken or spread out into a white coat; indispen- design^T^ ^.àming good effects in photographic annlicatio/of k^o ^ic alcohol or ether is to facilitate the he resm nnclor a very attenuated form, the spirit on the O^porated before the light effects its delineations ought to h ' J11 oår to obtain greater vigour, the metal °have an exquisite polish. There is more charm about ' afen on glass plates, and, above all, much greater delicacy.° commencing operations, the experimenter must carer ally clean his glass or metal plate. For this purpose, emery reeluced to an impalpable powder, mixed with alcohol, may be used; applying it by means of cotton-wool.- hut this part of rne process must always he concluded by dry-polishing, that no trace o 1 moisture may remain on the tablet. The plate of metal or glass being thus prepared, in order to supply the wash or coating, it is held in one hand, and with the other the solution is to he poured over it from a flask or bottle having a wide mouth so that it may flow rapidly, and cover the whole surface. is at first necessary to hold the plate a little inclined; hut as soon as the solution is poured on, and has ceased to flow freely and ^^d perpendicularly. The finger is then passed behind 2J!“9 ^à, in order to draw off a portion of the liquid, which, tending always to ascend, would double the thickness of , å^r must be wiped each time, and he passed y rapidly along the whole length of the plate from below, and on the side opposite the coating. When the liquid has ceased to run, the plate is dried in the dark. The coating being veil dried, it is to he placed in the camera obscura. The time required to procure a photographic copy of a landscape is from seien to eight hours ; but single monuments strongly illumi- nated by the sun, or very bright in themselves, are coined in about three hours. 1 a 111 “ When operating on glass, it is necessary, in order to in crease the light, to place the plate upon a piece of paper with great care that the connection is perfect over every part as other mse confusion is produced in the design by imperfect reflection^ It frequently happens that when the plate is removed from the camera there is no trace of any image upon its surface”™ C