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.
How Far To Carry Development Of Plates That Are Over-Exposed. The development of an over-exposed plate depends entirely on how badly a plate is over-timed, and how early the plate has been restrained in the development. It is far better to over-develop a plate, and after fixing, reduce it, than to under - develop. By over-developing an over-timed plate, you are aiming to build up your highlights. You realize that your shadows have sufficient strength, but the strength of the highlights are not sufficiently in advance of the shadows. Therefore, you carry the development farther to build up the highlights, knowing that the restrainer used in the development will, to a certain extent, hold back the shadows while the highlights are growing in strength. In other words, by over-developing you produce stronger highlights, and then by finally reducing with red prussiate of potash
(See Chapter X (Varying Water Conditions. Their Effects Upon The Manipulation Of Sensitized Papers) on Reducing), you reduce the shadows equally, if anything, slightly more than the highlights and the result is a negative of proper contrast.
228. On the other hand, if you under - develop, you produce thin negatives with apparently plenty of detail but no contrast and no solidity, and absolutely no printing quality. Therefore, it is advisable until one becomes familiar with the proper developing of plates, under all conditions, to over rather than under - develop.
Desired Amount Of Bromide To Use. Bromide is used as a restrainer. The amount to use depends entirely upon how much the plate is over-exposed. By using a ten per cent, solution of bromide, the strength is such that a little more or less will do no harm; therefore, one can use bromide quite freely without any perceptible damage to the plates. After one becomes accustomed to restraining with bromide and after some experimenting with a few plates by first using, say, five or six drops, then if this is insufficient to restrain the plates properly, the next time try ten to fifteen drops. In this way one may soon be able to determine the necessary amount to use. The worker, therefore, should carefully note how much bromide he is using each time, and if the results prove that enough was used, or too much was used, govern himself accordingly the next time he develops an over-exposed plate.
How Long A Plate Should Remain In The Bromide. Where plates are very much over-exposed, it is advisable to place them, previous to developing, in a bromide restraining bath, the strength of which depends upon how much in your judgment the plate is over-timed.
231. A fair rule to follow would be: If you consider a plate overtimed three times the normal exposure, then a bromide bath of, say, three ounces of water with one-half ounce of a ten per cent, solution of bromide added thereto, allowing the plate to remain in this bath for one minute, should be sufficient restraining. The plate should then be transferred immediately to a normal developer with one or two drops of bromide added thereto. The more the plate is over-timed the longer it should remain in the solution. If extremely over-timed then a stronger bromide solution should be used. Practice alone will teach you the exact amount of bromide to use, and the length of time the plate should remain in the restraining bath. Bear in mind that the immersing of the plate in a bromide solution previous to development is advisable only in cases of extreme over-exposure. Ordinary over-exposure can be restrained by developing in old developer, or by the addition of a few drops of bromide added to a normal developer.