Put the Gelatine in the cold water, and allow it a quarter of an hour to soften and swell; it will then readily dissolve on applying a gentle heat. This may be done in a glazed saucepan or a pipkin of earthenware, taking care not to scorch the bottom part by too strong a heat. Next clarify the solution by adding to it, whilst barely warm, a tea-spoonful of white of egg (previously beaten up with a silver fork), and afterwards heating nearly to the boiling point. The Alcohol must now be added, to facilitate the coagulation of the Albumen. When this takes place and the liquid becomes clear, filter through a clean piece of cambric folded three or four times. If a hot water filtering apparatus can be obtained, the solution may be made to pass through paper; but as it tends to gelatinize on cooling, the ordinary mode of filtration commonly fails. The quantity of Alcohol in the above formula is greater than is usually recommended, allowance having been made for a partial evaporation of the spirit.
The filtered liquid may be poured into a flat porcelain dish, or a vertical trough, but in either case it will be necessary to stand the vessel in warm water, in order to prevent gelatinization.
The Collodion plate, thoroughly washed, is to be immersed in this solution and moved up and down for two or three minutes. It is then removed, drained on blotting-paper, and dried. The use of artificial heat in drying will be found a great advantage; it prevents the gelatine from settling unequally upon the plate. Those who possess an apparatus made purposely for drying plates by hot air, will experience no difficulty, but an ordinary deal trunk may be made to answer, with a little management. Cover the bottom of the box with blotting-paper, and having heated one or two "flat irons," place them in the centre: then range the glasses side by side, with the coated surface looking inwards; in a quarter of an hour, or from that to twenty minutes, the desiccation will be complete. If the Collodion plates are prepared in a room containing a fire, they may be reared up side by side at a distance of two or three feet, and in that way may be safely dried without fear of injury, provided white light be excluded.
When dry they can be stowed away in a box; all the precautions given at [page 293] being observed. The sensibility remains good for many days, possibly for weeks or months in cold weather.
Exposure in the Camera.—Allow from four to eight times the exposure of the most sensitive moist Collodion. On a clear summer's day, a sun-lit view may require one minute or a minute and a half, with a short focus Stereoscopic lens, having a diaphragm of a quarter of an inch diameter. The average time however with the same lens would be about twice as much, viz. three minutes.
Development of the Image.—Make a saturated solution of Gallic Acid in water by the directions given at [page 261]. Then dissolve forty grains of pure Nitrate of Silver in one ounce of distilled water. Pour into a flat porcelain dish a sufficient quantity of the Gallic Acid solution to flood the plate readily. Then measure it, and to each fluid ounce add ten minims of the solution of Silver, or five minims in hot weather. It is important that no discoloration should occur on mixing these liquids together, to obviate which, observe the following precautions:—Clean the porcelain vessel very carefully with Nitric Acid or Cyanide before use. Employ a pure solution of Nitrate of Silver; and mix it with the Gallic Acid, in preference to adding the Gallic Acid to the Silver solution (read the remarks at [p. 179]).
The picture may be expected to appear in five or ten minutes, and in one hour, or from that to four hours ([p. 298]), the development will be complete. It will not be necessary to keep the plates in motion, but simply to lay them side by side in the solution of the Gallic Acid. If in spite of all precautions the developer begins to blacken before the intensity has reached the proper point, it must be poured off and a fresh mixture prepared. This however will not often happen.
Lastly, when a full amount of opacity has been obtained, wash the plate with water, and fix it in a solution of Hyposulphite of Soda, or dilute solution of Cyanide of Potassium.
Failures in the process.—Stains in the development may arise from using dirty dishes, or glasses which have been left in Gallo-Nitrate of Silver and improperly cleaned. It must be borne in mind that these impurities are not visible to the eye, although they produce the effect of discolouring the developer. A thorough cleansing with strong Nitric Acid or Potash will prove a remedy.
Blisters, unless of large size, may often be disregarded, as they disappear on drying. General cloudiness may depend upon the film having been imperfectly washed. Irregular reduction at certain parts may be due to the Gelatine setting before the plate has become dry, or to stains produced by the finger applied to the upper edge of the plate.[54]