This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
After the exposure has been made on the plate or film there is still no visible image, and it is necessary to employ some means of changing the invisible image to a visible one, and, in so doing, make it possible to utilize this image as a means toward an end - which end is the finished print.
The sensitive silver salts in the emulsion of the plate or film have undergone an invisible change when exposed to the action of the rays of light - some of the particles have been affected by the light, while others remain as they were. It will be found when this exposed plate, or film, is placed in a solution composed of some oxidizing agent, called a developer, that a change takes place in the color of these light affected particles and they are thus rendered visible to the eye, and may also be built up to form an image varying in density according to the amount of the light action on the sensitive emulsion.
White objects, of course, affect the sensitive plate or film to a much greater extent than dark objects; therefore, those portions of the emulsion representing white objects will be much denser than the sections representing the shadows, and the degrees of light and shade between these two extremes (called half-tones) will be represented in that degree in which they affect the sensitive salts in the emulsion. In a general way, the developer is the agent which acts upon those portions of a sensitive substance which have been exposed to the light. One of the most popular, as well as satisfactory, developing agents is pyrogallic acid; therefore, the fundamental training, which is to receive first consideration, will embody this developer.
Apparatus And Material. It is essential, in order that accurate results be obtained and that waste material be reduced to a minimum, that you provide yourself, first with a room that is totally dark; a suitable ruby lamp; a supply of clear water; four trays; a graduate; etc.; also the necessary chemicals for mixing the developing solution, and the fixing bath. (See Pars. 8 to 13 of the Detailed Instruction on Dry Plate Developing.)
Developing. Prepare the developing solution according to the formula given in Par. 47, and in the manner described in Par. 49, and place in a graduate a sufficient quantity of this normal solution to thoroughly cover the plate or film. Close the dark room door and be sure that all rays of white or actinic light are excluded from the room. No light should be in evidence, with the exception of that from the ruby lamp. The developing tray should be rinsed with clear water and allowed to drain for a few seconds; then take the exposed plate and dust it carefully to remove the dust that might adhere to its surface. Now place the plate in the tray, with the film or emulsion side up. Holding the tray in the left hand, take the graduate of developer in the right hand, and, beginning at the end of the tray furthest from you, pour the developer quickly, yet carefully, over the plate, at the same time drawing the graduate towards you - in this way there will be an even " sweep" or flow of developer going over the negative and driving off of the surface of the emulsion all air. If this manipulation is carefully carried out no air-bells will form on the surface of the plate. Rock the tray gently and, although protecting the plate from the direct rays of ruby light, watch for the first appearance of the image, which in the case of a normal exposure should be from twenty-five to forty seconds. (Before proceeding with the actual development you should read carefully the Detailed Instruction regarding the Theory of Developing, also the Process of Developing which follows.)
A WINTER AFTERNOON.
J. S. Neary, Trenton, N. J.
Rinsing. After the plate has been developed it should be rinsed in clear water for a couple of minutes in order to remove all superfluous developer from the emulsion. The negative is now ready to be fixed.
Fixing. The fixing bath should be prepared previous to developing, and should be made in accordance to the directions given in Par. 57. When the plate has been fully developed and rinsed in water it should be placed in this fixing bath until all traces of the unacted upon sensitive salts have been removed. The theory of fixing is very fully described in Pars. 26 and 27.
Washing. When the plate has been fixed it must be washed for half an hour either in running water or in six to ten changes of water. Great care must be given to the final washing, as it is very essential that not only the hypo be removed but that all chemicals be thoroughly washed out of the emulsion, so that nothing but the metallic silver image remains.
Drying. The plate should be dried in a draught if possible, yet be sure there is no dust in the air, for any particles which come in contact with the gelatine emulsion will adhere to it. The temperature of the room should not exceed eighty degrees. It is advisable to have the plate dry in from two to four hours.
Preserving The Negative. When the negative is dry it should be placed in a negative preserver (manila envelope) and full data recorded on the outside of the envelope. Important items which might be included in this data are: subject, brand of plate, weather conditions, make and speed of lens, size of diaphragm, exposure, developing agent or developing formula, and other information of value for future reference.