If the blacks do not come up, and if the tapping results only in removing ink from them, the exposure has been too short for use of the litho ink, or the swelling has been excessive, and the proper thing to do is to try successive mixtures of litho ink with various proportions of copper-plate ink, at first very small, then more and more, until inking takes place easily. If, in this way, it is found necessary to use copper plate ink almost pure, it may be thought that the print is too damp. Let the print dry, after having cleaned off the ink, and swell it less at the next attempt.
Finally, should the gelatine be covered uni formly with hard ink, or should, at any rate, the whites and greys of the image take the ink in the same degree, the exposure may be judged to have been excessive, or the swelling insuffi cient. Further swelling may be tried, but the result will probably be of mediocre quality.
It is always best to begin inking in the most important part of the picture. After application of the ink by the gliding and twisting of the brush, a light tapping takes away the excess of ink in the whites and causes it to penetrate the shadows. A very similar result may also be obtained by a rapid sweeping with the tips of the hairs. Portions of the picture of less interest are then lightly brought up with a brush almost free of ink, then progressively strengthened to the degree deemed correct.
At any moment the work can be wiped out with a pad of cotton-wool impregnated with petrol, followed without delay by a soft sponge well charged with water. After this, the print may be replaced in warm water to swell, or in ammoniated water.
Alterations in the composition of the ink allow various depths of tones to be obtained and controlled at will, the gelatine retaining the ink readily according to the softness of the latter. Parts treated with the soft, which may be thought too heavily inked, may be lightened by tappings with a brush charged with hard ink, which will restore the lost contrasts, by virtue of the greater stiffness of the ink resulting from the mixture.
Pure whites may be made with a small brush wetted with water. Shadows, on the contrary, may be obtained with a brush which has been charged with petrol ; the flat tone thus obtained is afterwards modelled by tappings.
Hairs and particles sticking to the picture are easily removed by touching them with a bit of hard rubber, shaped to a point, the mark thus made being removed by tappings. The same rubber is also useful for obtaining a pure white accent.
After each stage of the inking process the brushes should be well cleaned, first with petrol, then with gasoline. After rinsing, they should be hung up, hairs downwards, to dry.
686. Drying and Cleaning the Print. Whilst a print dries fairly rapidly if on an unsized paper, such as those generally used by printers, owing to the penetration of the greasy matter into the porous paper, ink on a layer of gelatine dries only very slowly. Thus the print remains in a tacky state for a very long time, and contact of anything with the image is liable to remove the ink or smudge it. In order to dry it, the
print should be pinned by the four corners to a wooden board or a stout card, and left to itself for several weeks.
To hasten drying, and at the same time to avoid the shiny appearance given to the print by oil unabsorbed by the paper, it is practicable, after at least a week of spontaneous drying, to subject the print to a grease solvent, such as petrol or carbon tetrachloride (the latter having the advantage of being non-inflammable), used in a dish, with avoidance of any rubbing of the picture. After leaving it in for a few minutes, the dish is rocked from time to time, and the print then taken out, drained, and put to dry. The image is then perfectly matt and is free from any tendency to set off on to any object with which it comes into contact. It even resists energetic rubbing fairly well or even the pressure of a dry-mounting press.
687. Special Instructions for Obtaining Prints by Transfer. Whilst a good print may be obtained on any paper having a matt coating of unhardened gelatine, even when very thin, a transfer is obtained easily only with a paper having a relatively thick coating of gelatine, and presenting very strong relief. It is advised, especially for first trials, to choose fairly strong, though not harsh, negatives.
A print inked with litho ink never works so well as one inked with copper-plate ink. Though the image may be of ample vigour, it does not follow that the transfer will be so. The full quantity of the ink never appears in the transfer, and, in parting with its ink, the print is generally less effective when the ink is hard than when it is soft. It may be said that copper-plate ink, stiffened, if need be, with a very little litho ink, or softened with a little oil colour, is the normal ink for transfer printing.' When several transfers are successively taken from the same print, inked each time with the same ink, it is found that the contrasts increase from one print to the next. Even if the first print is a little grey, the fourth print will probably have blacks so dense that all detail will be lost. This is because the gelatine becomes capable of absorbing a greater quantity of water after each passage through the press, with proportionate increase in the relief of the image. Indeed, for this effect it is not necessary to make actual transfers ; the passage through the press of the gelatined sheet between two clean pieces of porous board is able, when repeated several times, to cause the gelatine to absorb such a, quantity of water that it rejects even copper plate ink. This " blank printing " (preparation) is often made use of for facilitating the inking of prints intended for transfer. When the gelatine is thus excessively swelled it is sufficient to allow it to dry and then to re-moisten it to the desired extent, in order to continue the printing, if so required.