Читать книгу A Handbook of Illustration - A. Horsley Hinton - Страница 8

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REPRODUCTION BY HALF-TONE PROCESS.

From the processes with which I propose to engage my reader's attention, wood and steel engraving, and kindred methods, stand apart.

Were we dependent upon these alone, not one-thousandth part of the illustration matter of to-day could ever have been produced, encumbered as the older methods are with the two things which, in the production of anything "for the million," are serious drawbacks, namely, time and expense of production.

Whilst these older methods undoubtedly possess characteristics which will always give them a peculiar value, and secure for them immunity from extermination (and make them, indeed, essential for certain purposes), there was long ago felt a need for a method of rapid reproduction unattended with individual artistic skill on the part of each worker employed, and, above all, free from heavy expense. Such a need has been more than met by what we now know as the mechanical processes. I say more than met, because, gradual improvement in the processes themselves, and an increased knowledge of the particular requirements of these processes on the part of the draughtsmen or artists, has resulted in giving us a process which is not only rapid and cheap, but which produces prints of high quality and merit.

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.

(Original 14 x 11 inches.)LINE REPRODUCTION FROM PEN AND INK.

Beautiful as many of these are, they can only be applied where the expense attending them and the slower printing is not an objection, and where letterpress is not required on the same sheet at the same printing. Printing matter can of course be afterwards introduced, but this must be by a second operation.

We have now left for consideration the relief processes, in which the design to be printed is produced similar in character and appearance to that of the movable letterpress type used by printers.

FEEDING THE CHICKENS.

(Half-tone from photogram. Original 14 x 11 inches.)

These processes are roughly divisible into two sections, "tone" and "line," to understand which I will refer the reader to the accompanying illustrations.

In these the image appears to be respectively composed of lines of varying strength and proximity in the one, and of tints ranging from grey to black in the other. If the latter be closely examined, however, or looked at through a magnifying glass, it will be found that what at first appears to be a flat even tint is composed of an infinite number of dots arranged in a reticulated or geometrical pattern. We will now see how this effect is produced, and what are the especial uses of this so-called "tone" or "half-tone" process.

THE HERON HOUSE.

Half-tone from photogram. (Original 14 x 11 inches.)