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.
1. BREAKING UP THE HALF-TONE ON THE NEGATIVE (AUTOTYPY).
Of the various methods by which a breaking-up of the half-tones can be obtained, the so-called “autotypy” is the one most used practically. With this process the half-tones are broken up in the negative.
As every important technical discovery is formed not at once, but must be made by a longer or shorter series of smaller discoveries or improvements in order to attain the hoped-for goal, so was it also with autotypy.
From the work of Paul Pretsch, Mariot, Brown, and Fred. E. Ives the present state of the certain and beautifully-working half-tone process gradually evolved, and the last process, which ought to be considered as the immediate predecessor, is far outshone by autotypy as now practised.
Early attempts were made to obtain a printable image on stone by breaking up the chromated gelatine film, so that an irregular so-called serpentine grain was formed on it, which corresponded {68} fairly well with the theory of lithography, but gave no precise lines and no beautiful gradations of stone. If the grain was somewhat too coarse the effect of the picture was lost, the tone gradations were too far apart, and only light and shadows were given; if the grain was too fine the stone was not printable.