A Manual Of Photography

THE COLLODION PROCESS. 263 operation, but do it systematically and quietly, at the same time not being longer over it than is actually necessary, for collodion being an ethereal compound evaporates very rapidly. Many operators waste their collodion by imagining it is neces- sary to perform this operation in great haste ; but such is not the case, for an even coating can seldom be obtained if the fluid is poured on and off again too rapidly ; it is better to do it steadily, and submit to a small loss from evaporation. If the collodion becomes too thick, thin it with the addition of a little fresh and good ether. Exciting the Plate.—Previous to the last operation it is necessary to have the bath ready, which is made as follows:— Nitrate of silver ................30 grains. Distilled water ............................1 ounce. Dissolve and filter. The quantity of this fluid necessary to be made must depend upon the form of trough to be used, whether horizontal or vertical, and also upon the size of plate. The kind used by Mr. Horne is the vertical, though many still prefer the former, and attach, as before described, a piece of Indian rubber to the back of the plate as a handle whilst applying the collodion, and to keep the fingers from the solution whilst dipping in the bath. With the vertical troughs a glass dipper is provided, upon which the plate rests, preventing the necessity of any handle or the fingers going into the liquid. If, however, the glass used is a little larger than is required, tins is not necessary. Having then obtained one or other of these two, and filtered the liquid, previously free from any particles of dust, &c., the plate is to be immersed steadily and without hesitation, for if a pause should be made at any part a line is sure to be formed, which will print in a subsequent part of the process. The plate being immersed, must be kept there a sufficient time for the liquid to act freely upon the surface, particularly if a negative picture is to be obtained. As a general rule it will take about two minutes, but this will vary with the temperature of the air at the time of operating, and the condition of the collodion. In very cold weather, or indeed anything below 50° Fahrenheit, the bath should be placed in a warm situation, or a proper decomposition is not obtained under a very long time. Above 60° the plate will be certain to have obtained its maximum of sensibility by two minutes' immersion, but below this temperature it is better to give it a little extra time. To facilitate the action, let the temperature be what it may, bhe plate must be lifted out of the liquid two or three times,