A Manual Of Photography

IMPROVEMENTS IN DAGUERREOTYPE, 47 is decanted. It is also a little coloured, but remains very limpid. “Solution of Chloride of Gold and Platinum.—In order not to multiply the solutions, I take the ordinary chloride of gold, used for fixing the impressions, and which is composed of 15 grains of chloride of gold, and 50 grains of hyposulphite of soda, to a quart of distilled water. With respect to chloride of platinum, 4 grains must be dissolved in 3 quarts of distilled water ; these two solutions are mixed in equal quantities. "First Preparation or the Plate.—For the sake of brevity in the following description, I will abridge the name of each substance. Thus, I will say, to designate the aqueous solution of bichloride of mercury, sublimate ; for the solution of cyanide of mercury, cyanide ; for the acidulated oil of petroleum, oil; for the solution of chloride of gold and platinum, gold and platinum; and for the oxide of iron, rouge only. “ The plate is first polished with sublimate and tripoli, and afterwards with rouge,1 until a beautiful black is arrived at. Then, the plate is laid on the horizontal plate, and the solution of cyanide is poured on it and heated over a lamp, as in fixing an impression with chloride of gold. The mercury is deposited, and forms a whitish layer. The plate is allowed to cool a little, and, after having poured off the liquid, it is dried by rubbing with cotton and sprinkling with rouge. " It is now necessary to polish the whitish layer deposited by fixe mercury. With a piece of cotton steeped in oil and rouge tins layer is rubbed until it becomes of a fine black. In the last place, it may be rubbed very strongly, but with cotton alone, m order to render the acidulated layer as thin as possible. The plate is afterwards placed on the horizontal plane, and the solution of gold and platinum is poured on. It is heated in the ordinary manner ; it is then allowed to cool, the liquid is poured off, and it is dried by gentle friction with cotton and rouge. This operation must be performed witli care, especially when the impression is not immediately continued; for, other- wise, some lines of liquid would be left on the plate, which it is difficult to get rid of. After this last friction the plates should 1 If I prefer, for polishing, rouge to other substances, it is not because I recognise in it a photogenic property, but because it burnishes better, and because it assists in fixing the layer of gold, rendering it less susceptible of being removed in scales when heated too much. The galvanic plates, when there are neither marbles nor black stains (which sometimes happened origi- nally) receive better than others the application of metals, and, consequently, the chloride of gold adhering to it more firmly, is not removed in scales.