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Tones 579

papers, warm, time, gr, tone and developer

TONES 579. General Considerations. The emulsion of chloro-bromide papers is sufficiently slow for working by yellow light, but the light should not be so bright as when gaslight papers are being used.

As a general rule, the only tones for which these papers are used are those comprised between a pure black and warm brown. Some methods of working, however, will enable a. scale of colours to be obtained by direct develop ment on some of these papers, affording as long a range as that given by transparency plates for warm tones. These methods of working are not given, the same tones being obtainable on all development papers by subsequent toning.

These papers are extensively used in profes sional photography. They yield results of a quality comparable to those given by gaslight papers, but do not call for such power of lights in the printing machines and enlarging appara tus. In addition, they avoid the necessity for the after-process of toning for obtaining the warm black colour so greatly in favour. Their long scale of gradation renders these papers very suitable for printing from negatives of landscapes with clouds, which are frequently very difficult to reproduce on bromide papers.

The principles on which the warm tones are produced are the same as those previously described in regard to transparency emulsions for warm tones. In this case, also, the produc tion of an image of a certain desired colour with correct tone values requires that the extreme range of densities of the negative should be comprised within certain limits. But, if a par ticular colour is not essential, these papers can adapt themselves to negatives differing consider ably in character, or, when using the same negative, adjust themselves to wide variations in exposure.

580. Methods of Working. The beginner or the photographer who uses one of these papers for the first time, or even the experienced worker, should endeavour to print from a negative specially suited to papers of this kind, and then find the correct time of exposure by the test method already described (§ 553).

With regard to these test pieces at least, or, in the absence of tests, the first print taken from a negative, the development should be controlled by the Watkins method, in accordance with the following general instructions, or else by tenta tive determination of the value of the Watkins " factor " (§ 344) corresponding with that tone desired with a certain paper developed in a given solution.

Although some papers for warm tones may only give the desired results when they are used with the developer specified by the manufac turers, most will work perfectly with the follow ing developer (B. T. J. Glover, 1924)— Metol-Itydroquinone Developer for Warm Tones.

Metol . . . 18 gr. (2 grim) Sodium sulphite, anhydrous oz. (25 grim) Hydroquinone . 70 gr. (8 grim) Soda carbonate, anhydrous tho gr. (18 grm.) Potassium bromide . . r8 gr. (2 grm.) Water, to make . . 20 OZ. (i,000 c.c.) For use, this solution should be mixed with an equal volume of water.

A warm black tone is obtained by developing for a total time, according to the particular paper in use, ranging from 4 to 6 times the time of the appearance of the first details of the image. A brown tone is obtained by adopting as a " factor " a value ranging from 21 to 4, to be ascertained by trial.

The following table has been taken from Print Perfection, page 49 (B. T. J. Glover). The times of development are for a developer used at a temperature of 68° F. The strength of the light was considerably greater for the second paper than for the first On account of the extreme fineness of the grain of these images, it is often well to avoid the use of acid fixing baths, as they tend to weaken the half-tones. At any rate, prints should not be allowed to remain in an acid fixing bath for a longer time than is necessary for ensuring complete fixation.