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.
Under-Timing Portraiture. In portraiture the only real necessity for under-timing a plate is when photographing children, especially babies. Many times a very natural, pretty pose and cute expression of a child may be obtained if the exposure is made quickly, thereby slightly under-timing the plate. There are also times when you are apt to slightly under-time a plate, and not know it. The very best operators are likely to misjudge photographic color values and slightly under-time their regular work. Such plates must be treated and developed entirely different from properly exposed plates and the developing chemicals must be so manipulated as to give you the best results under the circumstances.
Action Of Carbonate Of Soda. You may be led to believe, because carbonate of soda is termed the detail producing chemical, and is used in developing to open the pores of the film, and permit the pyro (or whatever developing agent you are using) to build up the detail, that you can under-expose to any extent you please, and the carbonate, if used in sufficient quantities, will supply all detail required. Such is not the case. No chemical will supply detail where there has not been sufficient exposure to produce it. However, by the proper manipulation during development you can obtain all the detail that the exposure has produced, but such exposures cannot be developed with normal developer. They must be specially treated as under-timed plates. To develop in the ordinary way with a normal developer would give very unsatisfactory results - strong highlights, deep shadows and no detail. By altering the developer according to the methods given in this instruction, you can retain every value that is possible from such exposures, and many times save a plate, which if developed ordinarily would be worthless.
Developing. We will first consider the developing of a plate in which you are certain the deepest shadows are under-exposed. We will suppose that the subject is a landscape study such as we have described. Having made the exposures, now follow the developing of the plate so as to produce the best results. The plate without question is considerably under-timed in the most dense shadows, for the shadow portion of the plate had so little illumination that the exposure given has hardly produced what little detail was visible to the eye. Therefore, it is necessary to open the pores of the film so that the required chemicals may be given every advantage to act.
Chemical Action. Remember the effects of the different chemicals used when making up the developer. Pyro being your developing agent; carbonate of soda detail producing agent which opens the pores of the film so that the developing agent can act, thereby supplying detail; and sulphite of soda controls the color. Carbonate of soda alone is a strong alkali, and when used in connection with pyro without any color preserving chemical would give very harsh results and a yellow negative. Therefore, carbonate of soda must be combined with a color preserving chemical in order to retain control of the color of the plate.
105. In an under-exposure it is necessary to open the pores of the film as much as possible before admitting the developing agent (pyro) to act; therefore, place the plate in a very weak accelerating solution composed of carbonate and sulphite of soda, using them at the proportionate strength given in the formula for ordinary developing. Sulphite of soda, hydrometer test 70; carbonate of soda, hydrometer test, 40. Take of these stock solutions one ounce of carbonate, and one ounce of sulphite of soda, add sixteen ounces of water. Soak the plate in this solution, covering the tray so as to exclude all light and air. Allow the plate to remain in the solution for ten minutes, rocking it occasionally so that the accelerator will act evenly. While the plate is soaking prepare the developer as follows: (Regular formula for stock solutions will be found in Chapter II (Warm Tones On Gelatin Glossy Paper), Dry Plate Developing).- Of the stock solutions take,
Carbonate of Soda (40 hydrometer test)......
.... 1 oz.
Sulphite of Soda ( 70 hydrometer test).......
106. Add twenty ounces of water, and pour this developer in a tray. Place the plate in this tray, covering it to exclude all light and air, being careful that the plate is entirely covered with the solution, and occasionally rocking the tray to avoid streaks. Allow it to remain fifteen minutes, when upon examination you will find the plate has developed slowly, but not hard. Should the plate not be fully developed, prepare a new developer exactly like that in which the plates are developing, and proceed the same as before. Repeat this operation, renewing the developer every fifteen minutes until the plate is completely developed.