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.
Reducing The Plate. We will now suppose that you have your reducing solution prepared, and that you have sufficient quantity. Never try to reduce with a small amount of solution, as the results will probably be uneven. Eight ounces of solution in a 5x7 tray is sufficient for a 4x5 or a 5x7 negative. Place your plate, or film, face up into the tray which contains the solution. Rock the tray gently, but never in one direction, as the negative will start reducing very quickly. Examine it frequently, and always rinse under the tap, or in clean water before examining. If you fail to rinse the plate it will keep on reducing while you are examining, and often times plates in this way are reduced too far. When it is finally reduced to the desired stage, where you have sufficient softness to the highlights, rinse it off under the tap for a few moments, and then place it back into the hypo for at least ten minutes. By placing back into the hypo the color of the plate is preserved.
Plate Appearing Yellow. If the plate after reducing appears yellow, or at least a deeper color than you desire, you have not had sufficient hypo in the reducing bath. Sometimes the plate is yellow before reducing. In such cases you should not expect to change the color in this bath, as the reducing bath is not intended for clearing; in fact, it is more liable to increase the color. However, you may reduce the plate exactly the same as if you had the desired color, allowing for the changing of color. Then after fixing properly, and thoroughly washing the plate to eliminate all hypo, place it in the following clearing bath: -
Clearing The Plate Or Film. Dissolve four ounces of pulverized alum in one pint of water (sixteen oz.) Place this in a bottle, and label " Alum Stock Solution." Of this solution pour one-half-ounce into a tray, and add ten ozs. of water, and three drops of sulphuric acid C. P. Place your plate in the tray, and rock it freely. The color should disappear in a few minutes. If the bath works slowly, strengthen by adding more alum. When you secure the proper color remove the plate, and wash in plain running water for fifteen minutes, then place in the rack to dry. If you have no running water change the water on your plate about fifteen times. The sulphuric acid, even when combined with the alum, acts as a reducer if used in excess quantities. Therefore, if not used cautiously it will reduce the strength of the plate, as well as clear it. If too strong an alum bath is used it will cause the film to pucker.
Reducing Plates After They Are Dry. Caution:- Never try to reduce a plate until it is thoroughly fixed; to do so will produce a green color, and the plate is liable to reduce in spots. When reducing a plate that has been dried, it is a good plan to place it first in cool fresh water for a few minutes; then transfer the plate to the regular hypo bath, and allow it to remain about thirty minutes. Finally, without rinsing, place the plate in the reducing bath, rocking the tray gently. Never allow the solution to settle on the plate for a moment, or it will be streaked.
272. Life of Reducing Solution, and How to Keep
It. - Note. - Red Prussiate of Potash, when mixed with hypo, decomposes very rapidly, and sometimes becomes worthless after immersing a half dozen plates. If more than this number are to be reduced, a new bath should be made up. The reducing should be done in the dark room by good, artificial light. A strong daylight is not advisable, as it affects the solution, and naturally shortens the life of the reducing chemicals.