If we desire to get soft prints from a contrasty negative, we may use different methods. The simplest way is the use of a very rapid and consequently soft working paper. Ordinarily, however, this method is not sufficiently helpful. We must therefore also use suitable methods in later steps of the process, such as making the difference in swelling in the gelatine layer as small as possible in order to bring down the contrast, or inking up with soft inks.
A very reliable process for the production of soft prints or enlargements, even from contrasty negatives, is the following: the proper exposure for the densest portions of the negative should be first determined by means of a trial strip; then a full sized sheet of paper is exposed for exactly the time which has been determined, soaked in water until it is perfectly limp, and then placed in the developer. As soon as the first outlines of the image appear, the print is placed in a dish of pure water and allowed to lie there, film down. As soon as development has ceased, the print is taken out of water, dipped into the developer for an instant, and then immediately put back into the water. This method requires considerable time for full development, but produces prints or enlargements of especial softness. In this process, the developer which is absorbed by the film is soon exhausted in reducing the heavy deposit in the shadows, so that their development ceases, while enough developer still remains unexhausted in the other portions of the image to keep on developing. With very dense negatives, developer warmed to 25° C. (77° F.) can be used for the production of soft prints, but it must be very much diluted and carefully used, for development proceeds very quickly. Very soft prints may also be obtained by bathing the exposed bromide prints for about two minutes in a one per cent solution of potassium bichromate before development. This solution is thoroughly washed out of the print, and it is then developed.
Yet with very hard negatives all these remedies frequently fail, because the high lights are almost completely opaque to light because of their density. In such cases the negative itself must be improved. The ammonium persulphate reducer usually recommended for such plates, which acts more strongly on the lights than on the shadows, is, however, too uncertain in its action and may imperil the negative. It is better to adopt Eder’s chlorizing method, which enables one to improve too contrasty negatives in a convenient and certain manner. The principle of this process is as follows: the metallic silver of the negative is converted into silver chloride, which is again developed. This redevelopment is accomplished in such a way that the silver chloride on the surface of the film is first reduced to metallic silver; if development is continued, the reduction is continued to the bottom of the film. The delicate details, lying on the surface of the film, are thus first developed, while development of the overdense high lights, in which the silver deposit extends right through to the glass, is finished only after some time. It is therefore possible to stop development at the instant at which the shadows and half-tones are completely redeveloped, while the overdense high lights are, for instance, only half developed, and therefore only half consist of metallic silver, the lower half being still silver chloride. If the development is interrupted at this stage and the negative placed in a fixing bath, the still undeveloped silver chloride is dissolved. The shadows and half-tones thus retain their original values, and only the overdense deposits in the shadows are reduced. If the development is not stopped at this stage, but is carried through to completion, the negative is obtained unaltered, and the process can be repeated. If the second development is stopped too soon, the negative may be endangered and a very thin negative, lacking in contrasts, obtained.
The practical application of the chlorizing process is effected by bleaching the negative in the following solution:
| Cupric sulphate | 100 | g | 1 | oz. |
| Common salt | 200 | g | 2 | oz. |
| Water | 1000 | ccm | 10 | oz. |
As soon as the negative is completely bleached, which should be judged not only by transmitted light but also by examination from the glass side, it should be well washed and immersed in a slow-acting developer. All these processes can be carried out in daylight, and the second development of the negative is best controlled by frequent examination of the glass side. Development should be stopped when the shadows and half-tones are blackened, and there is still a whitish film of silver chloride in the high lights. Observation of the negative by looking through it is not advisable, for the negative very soon appears dense by transmitted light, because the metallic silver formed in development masks the silver chloride. As soon as the development is considered to have gone far enough, the plate should be rinsed and then fixed and washed in the usual manner. After a few trials, the judgment of the correct stage at which to stop development presents no difficulty.
I ordinarily use the chlorizing process in the following way, which practically excludes any possibility of failure: the negative is completely bleached in the solution just mentioned, and then washed for five minutes. It is then developed in any desired developer until it shows by transmitted light practically the same density, though in a brownish color, as it had before chlorizing. It is then rinsed off, placed in a solution of hypo, not stronger than two per cent, and carefully watched by light passing through the plate; it is taken out as soon as the desired stage is reached, well washed, and dried. In this modification of the chlorizing process the condition of the plate can be observed at every stage. The final negative, to be sure, does not consist of pure metallic silver, but as a rule of a combination of silver and silver chloride; but such negatives are sufficiently permanent for making prints and enlargements on bromide paper.
It is also advisable to lessen the harsh contrasts in a normal negative, either by masking the more transparent parts on the glass side, or by holding them back in printing or enlarging. Briefly, every possible means should be employed in order to obtain as good and harmonious a bromide print as possible.
The beginner is strongly recommended, however, in his first trials with bromoil, to start as far as possible with normal negatives and correct, and especially very clean, bromide prints. The use of this process for the improvement of the results from difficult negatives should be left for more expert workers.
It is often desired to provide landscapes with clouds, and this can be easily attained if enlargements are used as the basis for bromoil prints. Acceptable results are given by a process, which has often been recommended. This is, after blocking out the sky on the negative, to enlarge the landscape, develop the print and again place it while still wet on the enlarging screen and expose for the clouds, disregarding the existing image, and then develop the clouds.