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.
Obtaining Desired Contrast Of Over-Timed Plates. When a plate is only slightly over-exposed, treat it according to paragraph 32, Instruction, Dry Plate Developing. If, however, it is badly overexposed and you are developing according to instructions, and you cannot produce the desired contrast, it is because you did not allow the plate to remain in the restraining solution long enough before transferring to the normal developer. Or, if the plate was started in the normal developer, you may have allowed it to remain too long in this developer before checking or restraining. In either case if the plate shows flatness throughout the development, you must then over-develop to an extreme, and after fixing the over-developed plate then reduce it according to Instructions on Reducing Over-Developed Plates.
Obtaining Clear Shadows. You can only retain clear shadows in developing, should the plate be over-exposed, by the proper amount of restraining, either by the use of sufficient bromide, allowing the plate to remain in the bromide solution sufficiently long to properly restrain the shadows from developing before transferring the plate to the normal developer; or, by the use of old developer and the plate remaining in this old developer sufficiently long before transferring to the normal developer. The amount of restraining all depending on the amount the plate is over - timed. Bear in mind at all times that a plate that has been started in normal developer which proves to be over-timed will be fogged, and sort of a veil will appear over the shadows if the plate is allowed to remain too long in normal developer before restraining, no matter what restraining methods you use.
223. It is, therefore, evident that the first few moments the plate is in the developer are the most critical ones. It is during these moments that you must watch the progress of the plate, and the instant it shows signs of over-exposure the proper restraining must be done at once in order to retain clear shadows.
224. Again, you cannot expect to obtain clear shadows if your developing light (ruby light) is too strong. A light which would be perfectly safe, for correct exposures, may not be safe for over-exposures. The developing of an over-timed plate is slower than that of a properly exposed plate; consequently, the over-timed plate is exposed to the ruby light longer than a normally exposed plate, and, therefore, is subject to more or less fog from this light. It is well, under such conditions, to do your developing farther away from the ruby light so that only weak light falls upon the tray containing the plate and developer.
225. Sometimes high temperature in the developer or developing room, will cause foggy shadows. Constant placing of the warm fingers in the developer will warm the developer, and the solution exposed to the air for a long time is apt to become the same temperature as the dark room, and will, therefore, cause fog.
226. It is advisable when your plate is placed in a tray of restraining developer to place a cover over the tray, but do not neglect to rock the tray, because this is necessary to insure even development.