Various Methods of Development 381

developers, grain, developer, exposure, develop, ment, negatives and fine

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The user of miniature sizes is not only re stricted in the choice of methods of develop ment, but also in the choice of formulae. Some developers in given conditions produce, as a matter of fact, images in which the grain is less visible than that of negatives developed in more energetic and more rapid developers, and they are therefore better suited for the considerable degree of enlargement necessary.

384. Automatic Development. Numerous f or mulae have been published giving a fixed time of development, or a series of times each corre sponding with a certain and applicable either to one brand of plates or films, 2 or to all brands without distinction.

The best of these methods fail to take into account the extreme range of luminosities of the subject, or the variation in the speed of develop ment of various batches of a given type of emul sion, 3 or, finally, the inevitable variations in the composition of the developer. They cannot there fore produce negatives of the same contrast, all indiscriminately suited for the same method of positive printing. But all negatives thus produced will furnish satisfactory prints if the exposure of the plate or film has been ascertained with an exposure meter (§§ 324-325), and if a suitable method of printing is chosen for each negative.

By way of example we give here the formula, recommended by the Kodak Co. for the develop ment of its films (roll film and film pack), with the times of development corresponding with the various temperatures. (This developer must be compounded only at the time of use)— Soda sulphite, anhydrous . . 40 gr.

(4-5 grm-) Soda carbonate, anhydrous. gr grm.) Pyro . . . 15 gr.

(.-75 grm.) Water, to make 20 Oz.

(1,000 c.c.) Owing to the extreme dilution of this devel oper, it must be considered as completely exhausted after using once.

This method of development can be applied, after preliminary trials, to almost all the de velopers specified in the paragraphs below.

385. Fine Grain Developers. While the graini ness of a negative depends much more on the character of the emulsion than on the composi tion of the developer, so-called fine grain developers do, however, possess several notable advantages in all cases where it has been ble to give an ample exposure,' the best of these developers requiring double the exposure that could be given if a more energetic developer were used.

It is evidently always possible to obtain a tine grain image by stopping development at a time when the largest grains, which are the most rapid, are still only partially reduced, com pensating by appropriate printing the lack of contrast in such negatives, but it is found that to obtain in this manner a fully detailed nega tive, it is necessary to increase the exposure. The only developers that can be regarded as fine grain developers are those which for a given gamma value develop weak light impressions and, therefore, do not require an excessive over-exposure.

To obtain in areas of equal density, developed to the same gamma, a graininess less than that given by usual developers, it is necessary to restrict the expansion of the silver outside the limits of the initial grain and to diminish the risk of a joining up of adjacent grains. To do this, the swelling of the gelatine must be reduced to a minimum by decreasing the alkalinity of the developer, and increasing in it the total concentration in salts (doses of sulphite near to saturation). This weak alkalinity usually im poses the use of developers with a high reduc tion potential. The effect is completed by super ficial dissolution of the silver halide of each grain, either by means of sodium sulphite in high concentration, or by the addition of other solvents in small doses (animoniacal salts, hyposulphite, etc.) ; these solvents, however, produce a useful effect only if development is fairly slow.

Most of these developers distort the density carve by retarding, from the start, the develop ment of the high lights' ; owing to their weak alkalinity they are, in fact, very sensitive to the influence of the soluble bromide formed in the layer of emulsion, but act energetically on the image of the shadows when the developer has a high reduction potential. Paraphenylene diamine (A. and L. Lumiere and A. ieyewetz, 194 or orthophenylenediamine developers constitute a very special case. These developers, which have little energy, are very active sol vents of silver halide. In the absence of other developer, and being rendered only weakly alkaline, they require considerable over-expo sure, and do not permit of sufficient gamma being obtained, but they can be accelerated by adding other developers, and then form the most efficient of the fine grain developers.

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