CHAPTER III
THE INKING-UP
The Production of the Differential Swelling.—In the chapter on the bleaching we fully explained the processes which take place in the gelatine film under the action of the bleaching solution, and that the most important result of the bleaching process, aside from the disappearance of the silver image, is the formation of different degrees of swelling corresponding to the primary image, which in their totality form the tanned image produced in place of the photochemical image by the bleaching.
For the success of the bromoil print, it is now of the utmost importance that the different capabilities of swelling, now latent in the gelatine film, should be satisfactorily utilized. It is obviously possible to produce this swelling in very different degrees. The colder the water used for the swelling, the smaller the difference between the lights and shadows, while the warmer the water the more this difference is accentuated. If, for example, a print prepared for the bromoil process is placed in cold water and allowed to swell for some minutes, the existing capacity for swelling will only be excited to a slight degree. The high lights of the invisible image only take up a little water, and when dry are differentiated from the shadows under oblique visual examination by a very delicate gloss or not at all. If this picture is now worked-up with greasy ink, a print is obtained with a short scale of gradation, and its tone values are usually less satisfactory than those of the original bromide print. If, on the other hand, the print is placed in very warm water, the swelling of the gelatine reaches a maximum. The high lights are very much swollen, even the half-tones are somewhat raised, and the shadows, which do not absorb water, appear sunken. The result of the swelling in such warm water in this case is the formation of a very pronounced relief, that is not only visible, but is almost perceptible to the touch. If such a picture is inked up, a bromoil print is obtained, the contrasts of which are much stronger than those of the original bromide print. Between these two extremes there is obviously a whole series of intermediate stages, the suitable employment of which permits of the most varied gradations.
As already mentioned, the capacity for swelling of the different makes of bromide papers is not the same in baths of the same temperature. This fact, however, argues neither for nor against the usefulness of the various bromide papers. It makes necessary, to be sure, a certain care in the use of a paper, the qualities of which are unknown. If one has to deal with such a paper, the prepared print should first be soaked in quite cold water; it should then be removed from the water, placed on a support, dried in the manner to be later described, and examined by oblique illumination as to whether the high lights show by a slight gloss that they have absorbed water. This will be the case if the image shows well swollen high lights; if they are not present, it will hardly be possible to find distinctly glossy places. In any case one may begin with the inking-up, prepared, as will be explained later, to increase the swelling if necessary during the inking-up by immersion in warm water. If on the other hand, the print, when taken from the cold water, distinctly shows places where differences of swelling are shown by a gloss or even a delicate relief in the film, the work may be proceeded with, without further trouble.
Under any circumstance one should be careful at first in the production of the differential swelling. There should rather be no relief than too pronounced a one; for differences of swelling that are too small can be easily and satisfactorily increased during the work; on the other hand it is scarcely possible again to reduce too strong a relief. While learning, or when using an unfamiliar brand of paper, it is therefore advisable to allow the sheet to swell first in cold water and to carefully begin the inking-up. Only if this is not satisfactory, should a warmer bath be used and the inking again tried. This method is, however, dealt with more fully in the section of Chapter III, entitled “Different Methods of Working” ([page 85]).
The Properties of the Relief and its Influence on the Character of the Picture.—In order that the following explanations may be understood, an important property of the prepared and dried gelatine film must be mentioned.
The film of the prepared print, in which the differences of swelling necessary for the formation of the bromoil print are latent, develops variations of relief when it is placed in water. Then the untanned high lights absorb water, as already described, while the hardened shadows do not absorb it. The result of this process is the formation of those swellings, which, when they have attained a certain degree, are characterized by the formation of a relief.
A definite degree of swelling corresponds to a definite temperature of water. This swelling disappears again if the film is dried. The gelatine has, however, acquired the property of again attaining the same degree of swelling when immersed in water at any time after drying, even if the temperature of this water be a good deal lower. A print, for example, on which a certain relief has been produced in water at 35° C. (95° F.) and which has given up this water again because of drying, again attains the same relief if immersed in ordinary tap water at 10° C. (50° F.). If, however, this print after drying is immersed in water at 40° C. (104° F.), that is in hotter water than that first used, a still higher relief is obtained, and again in a similar manner, after drying, it will attain this higher relief when immersed in water at any lower temperature.
The degree of swelling that is once attained can, therefore, so far as the resistance of the gelatine film will permit, be increased, but it cannot be reduced, if the print as a whole is not subjected to a tanning, as with formaldehyde, a process that is not easily controllable. This peculiarity of gelatine makes it necessary to go to work carefully in the formation of the relief, so as not to carry the latter too far. If the work is begun on a too low relief this can be easily increased to the necessary height, as will be shown later, absolutely without any regard to any inking up that may have been done. On the other hand, if the formation of the relief has once been carried too far, as a rule the print can not be used, although reduction of the excessive swelling by a tanning agent may be attempted.