It will of course be at once apparent that in order to get our illustration into the printed pages of book or newspaper we must first transfer the original to a plate, or block, and then so manipulate the surface that, like a printer's type, it shall take the printing ink in such manner as shall leave an exact imprint upon the paper, or other surface, upon which it is pressed.
The transfer of the original is accomplished by photography. The preparation of the surface is effected by a chemical or mechanical process. Correctly defined, these processes are "photo-mechanical," and such are generally understood by the literally ambiguous title "process," which is colloquially applied to all such methods.
It is not the intention of the present book to give instructions whereby to work the processes, beyond a general outline which shall make the illustrator acquainted with the method in which his drawing or photogram is utilised. This knowledge will enable him, to some extent, to adapt himself and his work to its special requirements.
Photo-mechanical processes are of two kinds: those by which the image is ingraved, known as intaglio, and those in which the image is produced in relief, or relievo. In the first of these the result is more or less similar to an ordinary engraved copper-plate, which, being wiped after inking, retains the ink in the engraved or indented portions, and prints accordingly. The intaglio processes are confined to what is known as Photogravure, or Photo-etching, and modifications thereof. This will not engage our attention, for, beautiful as are its results, it is comparatively expensive, and lacks that characteristic of speed which has made the relief processes so useful. The engraved plate must be printed separately; it cannot be set up with type and printed as letterpress. At the same time, in order to clear my reader's mind, and my own course, before proceeding further, mention may be made of other separate-printing processes, such as Collotype[1] (also known under many fancy titles), in which the image is printed on a machine or press from an inked gelatine surface. These can easily be distinguished by the image having a perfectly even appearance as though produced by a water-colour wash, without grain, reticulation, or lines. Photo-lithography, in which, as the name implies, the picture is transferred on to stone, from which it is then printed as in ordinary lithography, may also be mentioned here.
HALF-TONE FROM PHOTOGRAM; HIGH LIGHTS STRENGTHENED WITH CHINESE WHITE.
Another beautiful process of reproduction is the Woodbury-type, named after its inventor, Walter B. Woodbury, in which a bichromated gelatine film is exposed under a negative, and the soluble portions afterwards removed by hot water. The resulting gelatine relief, which contains a facsimile picture, is allowed to dry, when it becomes as hard as stone. It is next forced by hydraulic pressure into a sheet of polished lead, leaving therein an exact counterpart of its every elevation and depression. The lead plate (intaglio) is next placed in a handpress, and flowed with a pool of hot gelatinous colour; a piece of paper is next placed on top and pressure applied, when all surplus colour oozes from the sides. After a few moments, when the gelatine becomes sufficiently cool, the paper bearing its delicate gelatine print is pulled off and dried.
LINE REPRODUCTION FROM PEN AND INK.