To reproduce an old chalk drawing so that it might be successfully transferred to stone and printed in the usual way, would be practically impossible by any other process. In copying through a ruled screen many of the delicate contrasts of light and shade would be so reduced as to become almost valueless, consequently the print loses both in artistic and expressive power. In contradistinction to this a natural grain exhibits no harshness or indistinctness in the gradations of tone, and retains its clearness and sharpness throughout the printing operation.
Reverting again to the half-tone ruled screens, it may be well to state that small prints, being usually subjected to a closer inspection than large ones, must be reproduced with great attention to the finer details to ensure a certain amount of fidelity, and for this reason a screen with fine rulings must be employed. Naturally, stronger and more vigorous reproduction can be secured with the coarser rulings, but the screen effect will be too pronounced for close scrutiny.
There is still much to achieve in photo-lithography, and it is probably owing to a full recognition of this fact that the progressive character of the process is maintained. Its commercial value is undoubted, and its successful application is chiefly a question of how and where it can be most effectively introduced.
The essential features of photo-lithography are:—
1. A copy or original in which the modelling is well defined, and the light and shade well emphasised, even to a point of slight exaggeration.
2. A negative in which the whites of the original appear opaque, with clear glass to represent the lines and solids.
3. A print which can be developed or inked up with a pigment sufficiently greasy in nature to transfer to the lithographic stone.