For the mezzotint another method is adopted, known as photogravure, and this is also a wonderful invention. A metal plate is slightly roughed—if it could be more roughed it would be better—and then a photographic relief in gelatine is put upon it and etched. The result is a plate resembling a fine grain mezzotint, but the prints made from it are always deficient in the blacks. To remedy this and other defects which at present seem to be inherent, an engraver generally goes over the plate with roulette and burnisher. The Photogravure has ruined the Mezzotint. The coating of the copper-plates with steel largely adds to their life.
Then we come to the wood engravings, which are all perfectly imitated by the zinc block, made directly from the original drawing, and set on a wood block so as to range exactly with type in height. Wash drawings are closely copied by the half-tone process, which is also used with blocks that can be printed with type. The drawing to be copied is photographed through a glass screen very finely etched with minute lines crossing each other, so that the picture is ultimately represented by a series of little squares, black or white according to the tones of the original. But the whites are never quite satisfactory, the dots of the screen always show a little, so the dispossessed wood engraver has to be called in after all to touch them up with a graver. In America, where the half-tone process has reached a very high degree of excellence, the names of these helpful engravers are frequently added. A curious “shot-silk” effect is often seen in half-tone illustrations where the lines of the screen fall at a particular angle with the lines on the original. The same peculiarity sometimes shows in the ruled sky lines in the small nineteenth century line engravings.
The three-colour process consists of half-tone blocks printed in colours one over the other, but although they look well they are not particularly true to their originals. The reason of this is that each block is a little wrongly inked, as the tint of the pigment put upon it depends entirely upon the printer. He has of course a carefully coloured key given him to match for each block, but he never quite succeeds in doing more than get near it. There are line keys and colour blocks, and half-tone and colour blocks, and many other varieties of combinations of processes.
The half-tone process is certainly responsible for much charming and valuable work, but it has done one very great harm not only to itself but even to literature, it has been the chief cause of the introduction of clay-laden paper (see [Chap. III.]).
The beauty of photographic illustrations can be best seen in some of the recent French illustrated books in colour published by the Société des Amis des Livres. Other exquisite illustrations are to be found in Octave Uzanne’s books, many of them from the drawings of Paul Avril. The way in which many of these illustrations are made to show over the printed page is often quite charming.
BOOKS TO CONSULT.
Baer, L.—Die Illustrirten Historienbücher des 15 Jahrhunderts. Strassburg, 1903.
Bayard, E.—Illustrations et les Illustrateurs. Paris, 1898.
Blackburn, H.—The Art of Illustration. London, 1896-1901.
Bonnet, G.—Manuel de Phototypie. Paris, 1889.