A Manual Of Photography

THE COLLODION PBOCESS. 265 The next question also often asked is, how long must he the exposure in camera ? a question more difficult to answer than the last, without knowing something of the character of the lens and the intensity of light. Practice alone can determine, combined with close observation of those parts which should he the shadows of a picture. If, for instance, in developing we find those parts less exposed to the light than others developing im- mediately the solution is applied, then we have reason to suppose the exposure has been too long ; but if on the contrary they develope very slowly we have proof the time allowed has not been sufficient to produce the necessary action. In a good pic- ture we should see first the whites of a dress appear, then the forehead, after whicli we shall find, if the light lias been pretty equally diffused, the whole of the face and then the dress. The Development of Image.—To effect this it must be taken again into the room, and witli care removed from the slide to the levelling stand. It will be well also to caution the operator respecting the re- moval of the plate. Glass, as before observed, is a bad conductor of heat ; therefore, if in taking it out we allow it to rest on the fingers at any one spot too long, that portion will be warmed through to the face, and as tills is not done until the developing solution is ready to go over, the action will be more energetic at those parts than at others, and consequently destroy the evenness of the picture. We should, therefore, handle the plate with care, as if it already possessed too much heat to be com- fortable to the fingers, and that we must therefore get it on the stand as soon as possible. Having then got it there, we must next cover the face with the developing solution. This should be made as follows:— Pyrogallic acid ...........................5 grains. Distilled water ..........................10 oz. Glacial acetic acid ... 40 minims. Dissolve and filter. Now, in developing a plate, the quantity of liquid taken must be in proportion to its size. A plate measuring 5 inches by 4 will require half an ounce ; less may be used, but it is at the risk of stains ; therefore we would recommend that half an ounce of the above be measured out into « perfectly clean measure, and to this from 8 to 12 drops of a 50 grain solution of nitrate of silver added. Pour this quickly over the surface, taking care not to hold the measure too high, and not to pour all at one spot, but having taken the measure properly in the fingers, begin at one end, and