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.
Snap And Crispness. It is well after a plate has been developing in the old or restrained developer for some time, to place it in a fresh normal developer in order to give snap and more crispness, always being careful to rock the tray. The rocking of the tray must not be all in one way; first rock from you, and then from side to side. The action of the normal developer is apt to be quite rapid; therefore, the plate must be watched very closely and when the proper strength and snap have been obtained, remove the plate at once and rinse thoroughly and then fix.
Under - Exposure. In case the image appears slowly and with contrast, shadows remaining clear, highlights building up slowly, you will readily understand that the plate is under - timed. Then immediately place it in a tray of plain water, cover the tray and allow the plate to remain in the water for say ten minutes, after which conclude developing in normal developer. We advise covering the tray so as to keep not only the light of your ruby lamp from the plate, but also to prevent the air striking the developer, as this would have a tendency to oxydize and also change the temperature.
Extreme Under - Exposure. If the plate shows signs of extreme under-timing, make a new developer weak in pyro,using one - half the quantity of pyro and the regular amount sulphite and carbonate of soda and double the amount of water. In making up a developer with less of the developing agent, you will prevent the highlights from becoming too dense and harsh, and the weak developer will give the shadows an opportunity to gain in strength and detail. Conclude the developing in this bath instead of with normal developer. Your resulting plate will be clear in detail, with no harsh highlights.
Judging When Plate Is Developed. The greatest difficulty in developing a plate is to know just when to stop. Conditions have so much to do with the proper developing of a plate that it is hard to state exactly how to tell, under all circumstances, when to stop developing. A properly timed plate is fully developed and carried far enough when the contrast between the highlights and shadows is as you would desire it, and as it appeared on the ground-glass, taking into consideration that the plate loses some of its strength in fixing. Some brands of plates fix out more than others. For instance, a Seed plate will lose two degrees in a hypo bath, while others will lose one shade of density; so when judging if the plate is fully developed, you must bear in mind the brand of plate used and develop accordingly.
41. In considering an over or under-timed plate as to when it is fully developed, you must judge it for the same result as one properly timed, taking into consideration whatever effect the over-timing or irregular conditions may have upon it. Should the plate be slightly over-timed it will thicken (blacken) up more rapidly than if correctly exposed, and, therefore, must be carried farther, bv allowing to remain in the developer until the desired contrast - even in a very dense plate - is visible.
42. If the plate were removed from the developer with an even density throughout, but with no distinction between highlights and shadows, and then fixed, white it may be strong, it will lack the necessary contrast. Such plates must, therefore, be carried to the stage where the contrast between highlights and shadows is visible even in the most dense plate. The plate so developed can then be reduced and a good printing negative made of it.
An over-exposed plate under-developed will appear very thin and full of detail when fixed, but will have no printing quality, so it must be carried far enough to produce this result and stopped there.
43. Upon examining the plate (by looking through it, holding it up to the ruby light) during development, if you are in doubt as to whether the proper density has been obtained, you can, by looking at the back for the image, see how far through the film the developer has penetrated. If in looking through you find the proper contrast and the image also shows fairly clear on the back, you may know your plate is sufficiently developed. Do not depend, however, on looking at the back alone, for in some cases plates will be fully developed before the image appears on the back at all. This greatly depends on the thickness of the emulsion, which varies in different brands and also on the length of exposure.
44. For a plate that is slightly under-timed, necessitating weak, slow development, the image will appear on the back at an early stage and more distinctly than in a normal exposure in which the image may show very dimly or not at all, even when completely developed. You will notice that the highlights show through the film first, and if in looking through the plate the details appear weak, continue development until they are brought out some on the back.
Double Coated Plates. The beginner invariably under - develops double coated plates, as the extra emulsion adds to the general density, misleading one's judgment. For these plates the factorial method of development described in paragraphs 459 and 695 is recommended.