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.
Exposure. The amount of time necessary for the exposure must be judged by the amount of reduction, quality of lens and the intensity of light, and this portion of the work can only be learned by practical experience. A safe rule to follow is to expose about ten or fifteen times as long as you would a dry plate under the same conditions. It should be remembered, however, that exposures through the screen for half-tone work will require about four times that of a negative intended for line work.
982. With the exposure determined, and the plate being sufficiently immersed, the operator now returns to the dark-room, lifts his plate from the bath and drains it; then, leaning it against a support, which should be covered with a piece of clean blotting paper, he wipes off the back of the plate with a piece of soft tissue paper. Before placing the plate in the holder, a strip of blotting paper is laid on the trough or bar on which the plate will rest; this will take up silver waste during exposure and prevent rotting of the holder. (If the required exposure is for producing a halftone plate, care should be taken to see that the half-tone screen has been placed in proper position.)
Making The Exposure. The plate-holder is then placed in position on the camera, the slide is withdrawn and the cap removed from the lens for an exposure to obtain the shadows of the copy; then the cap is again placed on the lens and the diaphragm is changed for an exposure to obtain the middle tones, and after the cap is again replaced, a third change is made in the diaphragm and an exposure made for the high-lights. (In making an exposure for coarse screen work, only two diaphragms are used, one for the high-lights and the other for the shadows, as a con-trasty negative is desirable.) If the exposure is for line work only one diaphragm is used, the size of same depending upon the color of the copy and the amount of reduction.
984. The best results are obtained by changing the size of stops during the exposure, proportioning the time with each, to give good detail throughout, by making a part of the exposure with the small stop, a part with the next larger stop, and completing with a short exposure with the largest stop. In making negatives for half-tone plates, usually each operator is apt to work differently from another - for instance, some expose first for high-lights, then the middle tones, then the shadows, while others invert the order and expose for the shadows first.
985. Further, in making negatives for half-tones, an important factor is the regulation of the distance between the screen and the negative in the plate-holder - the finer the screen used, the closer it is placed to the plate.
Developing. After having made an exposure and replaced the slide in the holder, the latter is removed to the dark-room, which is supplied with a ruby light; then the negative is developed, using the formula already given. In this operation it is necessary to keep the plate moving so the developer will be in motion (the more of the solution that is kept on the plate the denser it will make the negative). When the whole picture is "up," stop the development by washing with a good flow of water under the faucet, and then use the fixing solution and again wash thoroughly, which must be done promptly after each operation.