Chapter V The Half-Tone Process for Photo-Lithography
The half-tone process is used in photo-lithography to reproduce originals which do not contain distinct lines or points, but closed tones, which are executed either in one or several colours. With this process any coloured picture, oil, water, pastel, indian-ink or sepia drawing, as well as any photographs from nature of living, moving scenes, or still life objects can be prepared for reproduction on the printing press.
I will first describe briefly the theory of the process, and then come to the practical part.
As regards the photographic part and the quality of the negatives, in the present state of this method of reproduction the same principles apply as in line reproduction; where they differ I will mention the same.
The duration of printing, the transfer of the image to the stone, as well as the other arrangements will be described in the different processes.
We divide this chapter again into two sections:
1. Methods in which the half-tone is broken up when making the negative.
2. Those methods in which the formation of the grain is effected after the negative has been made by some suitable means.