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Reduction Methods of After-Treatment Intensification

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METHODS OF AFTER-TREATMENT : INTENSIFICATION, REDUCTION, WORKING-UP, RETOUCHING 444. General Considerations. Of the various corrective operations described in this chapter, intensification and reduction are purely chemical manipulations, whilst the others, retouching, etc. (including the local application of intensifiers and reducers), arc processes requiring manual skill, and presuppose some artistic knowledge (ideas of values and ability to draw, knowledge of anatomy for those who are concerned with portrait retouching) and the mastery of a special technique (inversion of values). We propose to deal chiefly with chemical methods here, because retouching, properly called, cannot very well be taught from a book.

Under the name of intensification are included all processes which, after the negative has been made, allow of increasing the various densities of the image in such a way that the difference between the extreme densities is increased, as also is the contrast. On the other hand, reduc tion comprises all methods which allow of decreasing the different densities of a photo graphic image with or without decreasing the difference between extreme densities.

The operations of intensification and reduc tion were of great importance in days gone by, when negatives had to have almost the same range of densities in order to suit the few methods of printing which were then available, and, moreover, when the shadows in negatives had to be almost completely transparent lest the already long duration of printing in daylight became excessive.

The great variety in the characteristics of different sensitive materials now available allows of successful printing from negatives having widely different ranges of density. Thus, unless

a given printing paper is chosen a priori, one may almost always avoid intensification or reduction of the negative. Whilst intensification, as suitably carried out on a negative which has been fixed with the precautions advised, is an operation which does not entail much risk, the same cannot be said for reduction, in which there is always an element of uncertainty, especially when it is applied to an already dried negative. Moreover, in the case of very dense negatives, such as result from long exposure and normal development, it is often better to confine oneself to using a more intense light for printing, or a longer time of exposure, rather than to risk the destruction of the scale of tones by reduc tion. 1 In the case of a negative having a very great scientific or documentary value, it is usual to refrain, even in the most extreme cases, from all attempts at direct improvement. Instead, a positive transparency is made from the nega tive under the best possible conditions ; on this positive any intensification or reducing which may be necessary is carried out, and then a reproduction, forming an improved duplicate of the original negative, is printed. By taking the precautions necessary to preserve the sharp ness of the image in the course of successive printings, and by choosing for each one of the printings an appropriate method (§ 570), it is possible to obtain from a very mediocre negative, without any corrective operation whatever, a very satisfactory reproduction, in which the contrast is increased or diminished to the desired