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Various Methods of Development 381

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VARIOUS METHODS OF DEVELOPMENT 381. Formulae for Developers. Some photo graphers spend most of their time testing successively all the developing formulae that they see, even when they show but negligible differences irons other formulae previously tried (differences of the same order as those resulting from the uncertainty regarding the actual con tent in active substances in the products used). They attribute the success of other workers to the possession of some ideal formula, kept jealously secret, and making good all the failings of the photographer.

Except for some very special purposes, which require the use of developing baths of a composi tion considerably different from those of the usual type, any good formula is as suitable as another, and the best are generally not the most complicated. The choice between various cur rent formulae should be made more on account of cost than for technical reasons. It has often been said that the best developer is the one with which the photographer is familiar, and it is not by abandoning one formula for another at the moment that its use is becoming familiar that the best results can be hoped for.

Some ridiculous formulae have been published owing to mistakes in converting foreign weights and measures or to typographical errors. Chance coincidences have led some practical workers, with little experience of experimental methods, to recommend the addition of products which are completely useless. Putting such exceptions aside, success depends more on the judicious conduct of the operations than on the choice of a particular formula.

In the following paragraphs one or more developing formulae will be given as exemplars of the methods of development described. They are not claimed to be better than others, but they are as good as others and respond per fectly to any reasonable demand that may be made.

382. Rapid or Slow Development. Develop ment of almost lightning rapidity is certainly not at all advisable, for it can involve only the upper layers of the emulsion and can usually give only flat negatives' with numerous local blemishes. Also a solution which develops very rapidly must necessarily be a very concen trated one, in which the energy is pushed to the extreme limit by a large content of alkali, and such a developer is very costly and keeps badly. As a rule the strength of a developing solution is arranged so that development does not last much less than five minutes.

When a large number of plates or films have to be developed in a fairly short time, the development of several negatives at the same time becomes almost indispensable. It would be very inconvenient to arrange side by side the requisite number of dishes, and, moreover, with a development time of about five minutes, it would be difficult to watch the development of several negatives effectively. Development in a vertical tank is then resorted to. Both because of the large capacity of such tanks (where the use of a concentrated solution would be very expensive), and in order to have time to inspect the negatives, the developer is used diluted in such a manner that development lasts from io to 30 minutes.

From the point of view of the quality of the images, it is absolutely immaterial whether the negative is developed in five or in 30 minutes.

Under the fallacious pretext of correcting errors in exposure, there has been recommended from time to time the systematic use of very dilute solutions with which development may last one or two hours. A bath in which develop ment requires much more than 30 minutes has no advantage and has quite a number of disadvan tages : exaggeration of chemical fog, streaks due to exhausted products, and excessive swelling of the gelatine, which considerably increases its tenderness.

383. Methods of Developments. The profes sional photographer and the advanced amateur, working large or medium sizes on plates or cut film, and seeking above all the best possible quality in each of their negatives, can utilize methods correcting, as far as possible, errors in exposure, or permitting the character of the image to be modified to a certain extent. Such methods arc obviously not applicable either by the amateur beginner whose procedure is likely to be at fault, or by the user of a miniature size who cannot see any detail in the negative during development,' or by the photographer using a panchromatic emulsion that has not been desensitized, or finally by the D. and P. worker, who is compelled to work to delivery times that are ridiculously cut down and are, by the way, very detrimental to the quality of the work, so that he cannot examine the images during development or even sort out and treat separ ately films of different brands for which the optimum duration of development is not always the same.

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