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.
Developing Extreme Over - Exposures. In case the plate is very much over-timed, it may require more dense developing than for normal exposure. This you can do by simply allowing the plate to remain in the developer longer than usual, even in the restraining bath. This prolonged development may be necessary in order to produce the desired contrast. No matter how strong a plate is developed, it is not carried or developed far enough unless the desired contrast between the highlights and shadows is visible, even if the plate does appear extremely dense.
203. When the desired contrast is reached, the plate may be fixed in the regular hypo bath. After fixing, the plate should show a fine contrast and a beautiful negative except that it is very hard and dense and would not produce a good print. Therefore before washing place this plate in your reducing tray and reduce it to the proper strength. (See Instruction on Reducing.) After reducing, rinse off both sides in plain water, return the plate to the hypo bath for a few minutes and then wash thoroughly and place in the rack to dry. In case the plate is so much over-exposed that it becomes fogged, even in the restrained developer, then carry it as far as possible in the developer so that the plate is quite dense throughout. Then fix, after which reduce very thin - thinner than you desire the finished negative. This will remove all fog. Wash well, after which intensify to the proper strength. (See Chapter V (Purple Tones On Collodion And Gelatin Glossy Papers) for Intensifying.)
Reducing Over-Developed Plates. You will notice by reference to the instruction on Reducing that we recommend two different formulae for reducing, one of which acts on the highlights almost entirely. This is the persulphate of ammonia reducer. ( See paragraph 274.) The red prussiate bath, while it acts upon the highlights, also reduces the shadows. (See Chapter X (Varying Water Conditions. Their Effects Upon The Manipulation Of Sensitized Papers) on Negative Reducing.) Before reducing an over-exposed plate which has been purposely over-developed, you must examine the plate thoroughly in order to determine which solution to use. If your plate is strong in the highlights only, and the shadows are clear and about the proper strength, you must use the solution that acts mostly on the highlights, which would be the persulphate of ammonia. On the other hand, if the plate is developed quite evenly and needs a general reducing in both highlights and shadows, use the red prussiate of potash. You will find a plate which has been extremely over-exposed and over-developed should always be reduced with the red prussiate of potash, for the reason that both the highlights and shadows are very much too strong and an equal reduction is required.
Restraining The Plate Too Quickly. Caution: When developing a plate and you find it over-timed, do not be in too big a hurry to place it in the restraining bath; allow it to develop until you have secured the necessary detail in these shadows. However, in a very much overtimed plate there is danger of waiting too long. You must, therefore, carefully watch the plate and just as soon as you find that instead of the detail in the shadows gaining strength they are becoming flat - fogging over - at once place your plate in your restrainer. On the other hand, if you have not developed your detail before the plate has reached the re-strainer you will have difficulty in obtaining it afterwards. Your restrainer prevents the shadows from building up and permits the highlights to strengthen while the shadows are being restrained, or, in other words, the shadows have stopped developing.