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.
484. A great deal can be said in favor of tank development, yet unless one has carefully followed the previous instruction given on developing by the ordinary way, so that negative developing is thoroughly understood, it will not be possible to produce the desired results, or fully appreciate the value of this method of development.
485. Tank development is nothing more or less than developing with a diluted solution, causing slow development of the image, which latter is always commendable, for by means of weak solutions resulting in slow development, all classes of exposures may be developed in one and the same tank, and at the same time. The mechanical part of tank development is very simple. It consists in putting a number of plates into one tank, in which vessel they are held in an upright position, and surrounded with a weak solution of normal developer, at a certain temperature, which is allowed to act for a certain length of time. At the expiration of the required time for complete development the plates are removed from the tank, and fixed in the usual way.
Latitude In Development. There is a wonderful latitude in the time of development with tank developer. A plate may be developed in ten minutes or two hours, producing practically the same results, and this is entirely governed by the strength of the developer employed, and the temperature of the solution, which regulates the time for complete development.
487. To prepare a developer for tank development and a bath that will develop plates in a certain number of minutes, there are different ways of proceeding; one is to take your regular normal developer and dilute with water sufficiently to develop a normally exposed plate in the desired number of minutes. For instance, to dilute the normal pyro developer given for universal developing with double the amount of water, or twice as much water as you have normal developing solution, will give you approximately a twenty-minute developer, and diluting it three times gives a twenty-five-minute developer. (See Par. 467-470.) The accurate time, of course, can only be ascertained by a few trials.
488. One can disregard the exact time entirely, and judge the complete development by examination from time to time. Yet, it is best to handle plates as little as possible while developing, for the warmth from the hands changes the temperature of the solution, thus rendering the film soft, and easily damaged; and again, it is also well to know the exact speed of your developer, as more uniform results can be obtained, especially where all classes of exposure are developed in the same bath, and at the same time.
489. The most successful method to employ, however, is the factorial system, as explained in former instruction, for by means of the factor you can secure the exact time necessary for complete development, and we will, therefore, apply the factorial method for developing in this instruction.
490. For the convenience of those who have followed the developing instruction previously given, we will use our regular pyro formula, given for universal developing, and apply it to tank development.
491. In this instruction for tank development we supply the simplest methods that can be used, and which we have found practical. We would say, however, that to produce perfect negatives by tank development, it requires more than the mechanical work; one must exercise their best judgment, and prepare the chemicals very accurately. We advise applying the formula given herein without alteration until you become more familiar with the working of the bath. Remember to always keep the temperature as near sixty-five degrees Fahr. as possible.
492. It would be well after becoming familiar with the working of the bath to try a number of experiments, carefully making a memorandum of the strength of the developer, and the time required to fully develop a normal exposed plate. When once you have ascertained the strength of your developer, and the length of time necessary to produce the kind of negative that is best suited to the paper you intend to print on, tank development is then almost a mechanical process.
493. The two formulas supplied are based on the results obtained by experimenting, and by carefully observing the rules, and properly preparing the developer you will be able to produce good negatives. If, however, your first results are not as you desire, the method of changing the length of time development is extremely simple. The latitude is so great that it will rest entirely with yourself as to the results which you will produce.
494. In a former paragraph we made the statement that a plate might be developed in ten minutes, or in two or more hours, producing the same results. For example: In the former case the developer must be a great deal stronger than in the latter. To make the developer work slower it is only necessary to dilute with water. The weaker the developer the slower will be the process of development. In other words, more or less water will respectively slacken, or increase the speed of development. Usually to dilute a normal developer with an equal amount of water will require a little more than double the time of a normal developer for complete development. We recommend the pyro developer for tank development. However, for those who like the non-staining developers, we give also a metol - hydroquinone formula, and where the latter is employed not longer than a ten to fifteen-minute bath should be used, as long development with metol has a tendency to fog, even with bromide added. The pyro is the most commendable for general results, but should be made up fresh each day, for the action of pyro as a developing agent is such that even in a diluted solution, after a few hours' standing, whether in use or not, it becomes discolored and loses its developing power, and cannot be relied upon to produce uniform results; therefore, a fresh bath should be made up each day.