CHAPTER IV
AFTER-TREATMENT OF THE FINISHED PRINT
The film of ink on the dried bromoil print after the completion of the brush work is as a rule not very tender, except where much soft ink lies on the surface. It is not advisable, however, to put the print under pressure, as for instance in a printing frame, for under strong pressure the ink may still partially offset on the adjacent paper, so that the image is damaged. No pressure should be applied until after the removal of the fatty medium, which is described later.
When the brush work is completed, the whole surface of the bromoil print shows a slight gloss, caused by the fatty medium of the ink. The shadows show a stronger sheen, especially in those places where there is more soft ink, for soft inks contain more medium. The surface of the print, so far as the gloss is concerned, is like that of a finished gum print. But with the latter the gloss cannot be removed; when it is desired to get rid of the unpleasant property of gum prints, that the shadows are more glossy than the rest of the print, it is necessary to make the whole print glossy by painting it with a solution of gum. This is also the case with the carbon process.
With the bromoil process, on the other hand, it is easily possible to remove the gloss entirely. The shininess of a finished bromoil print is especially unpleasant when seen sideways, but, in certain cases, it imparts depth to the picture and may be made fairly inoffensive by glazing the print. Prints which are to keep their gloss must be exposed to the air for some days, protected from dust, until the ink has completely hardened. Until this has happened, the surface of the picture, especially where the ink is soft, is sensitive and ought not to be touched.
Defatting the Ink Film.—Before removal of the fatty medium from the ink, the print must be absolutely dried out. It must be so dry that it rings sharply when the finger is snapped against it. Also, the dish in which the defatting is to be carried out must not contain the slightest trace of moisture, otherwise trouble will be caused.
An easily volatile solvent of the fat, such as benzol, trichlorethylene, carbon tetrachloride, etc., should be poured into the dish, and the print immersed in the liquid and allowed to remain for some minutes with constant rocking. On account of the danger of fire from the vapors of benzol, no naked flame should be allowed in the room. Carbon tetrachloride (carbona), on the other hand, is non-inflammable; its solvent action, and that of the trichlorethylene, on fats, is much more rapid than that of benzol.
The film of ink is, as a rule, not damaged by the solvent, though care should be taken with prints which have been executed wholly or mostly in soft ink. With such prints it may happen that the ink is entirely dissolved in parts, or that irregular sharp lines and streaks are suddenly formed. Soft ink prints should, therefore, be allowed to dry for several days before they are defatted. By the use of very energetic solvents, such, for instance, as trichlorethylene and carbon tetrachloride, soft ink prints, as a rule, are completely dissolved. Benzol is, therefore, to be preferred in all cases.
The print should be removed from the liquid without touching the ink film, softened by the solvent. This evaporates fairly quickly, and now the bromoil print has an absolutely matt surface of great beauty. It is here naturally assumed that the fatty medium of the ink is soluble in benzol, which is usually the case.
The solution of the medium from the fatty ink, besides the removal of the gloss, has also the effect of fixing the surface of the picture and making it more resistant. While the film of ink before the defatting is fairly tender, it afterwards has a stability at least equal to that of a pencil drawing. The surface of the finished bromoil print is generally at least as little liable to damage as the film of prints prepared by other photographic methods. It seems as if the very minute grains of pigment contained in the fatty ink are made firmly adherent by the drying of the somewhat tacky gelatine film and therefore remain fixed even after the removal of the fatty medium. It is only from places in which a specially thick layer of soft ink was deposited, that a trifle of pigment dust can sometimes be removed by light friction.