Half-tones are occasionally printed on a kind of vegetable parchment, a paper which should be more extensively used since it will sometimes, but not always, give as good a reproduction as art paper, and the final result is more pleasing from the artistic point of view.

[Ill.u.s.tration: G. Oliver, del.]

RELIEF PRINTING

[Ill.u.s.tration:

Little maid, little maid, Whither goest thou?

Down in the meadow To milk my cow.

Fig. 1.--A wood engraving, by Edmund Evans, from the original drawing by Kate Greenaway.

Reproduced by permission of the publishers, Fredk. Warne & Co.]

RELIEF PRINTING

In order that ill.u.s.trations may be incorporated in the text, the blocks used must be in relief the same as the type; a mixture of intaglio and relief is impossible, for the whole surface must be level in order to be inked by the rollers, which deposit the pigment evenly, so that only one tone of colour--that of the ink--is possible.

Up to quite recent times wood cuts and engravings were the only means available for text-ill.u.s.trations, so that this method may next be considered.[A]

[Footnote A: See Trevira.n.u.s, C.L.: _Die Anwendung des Holtzschnitts zur bildlichen Darstellung von Pflanzen_.

Leipzig, 1855.]

WOOD CUTS AND ENGRAVINGS. The invention of ill.u.s.trating by means of wood blocks followed closely on the heels of the use of moveable types for printing. The Chinese were the first, as far as is known, to use these methods of printing and ill.u.s.tration; in the western world the first wood blocks date from the beginning of the fifteenth century.

All the earlier cuts were made, commonly on pear wood, on the longitudinal face of the wood, in technical language "on the plank,"

and seemingly, in many instances, were made from drawings in ink. By cutting on the plank, the craftsmen were enabled to make large blocks, but were prohibited from doing anything more than relatively simple and straightforward work. Such blocks are known as wood cuts; wood engravings were not made until the possibilities of a hard wood like box carved upon the transverse section were discovered at a much later date. This is, strictly speaking, wood engraving, an art which almost entirely, if not quite, superseded the older craft, on account of its great possibilities; indeed, wood engravers imitated metal engraving so closely as to deceive many. But such work was enormously laborious; for instance, in the case of a fishing net, if the string were to be printed black, the engraver would have to cut out hundreds of small diamond-shaped pieces of wood in order that the string of the net should be in relief. But few artists would do this of their own free will, and generally such laborious work will only be found in wood-engravings which were intended for the reproduction of ink drawings or other kinds of pictures where the lines, shading, etc., had to be faithfully copied. This point may be ill.u.s.trated by the accompanying cut (Fig. 2), which was made by my friend Mr. Geoffrey Oliver, who at the time was totally uninstructed in the art and knew nothing of its literature. It will be seen that he, quite unconsciously, treated his wood in the same way as an engraver would his metal; the result, of course, is just the opposite to metal engraving since the printing of the wood block is the reverse to intaglio.

[Ill.u.s.tration: Fig. 2.]

In fact, the cut ill.u.s.trates the three fundamentals of wood engraving; the white line made by cutting out the wood so that no impression will be obtained when printed; the white s.p.a.ce which is similarly obtained; and the black s.p.a.ce, which is made by leaving the wood untouched. It was, however, necessary to employ the black line, otherwise the tape with which the two men--the artist and his father--are measuring the trunk of the tree would be invisible where it crosses the sky. In a word, the little picture ill.u.s.trates very nicely the legitimate use of wood in the graphic arts.

As already remarked, the majority of the earlier wood cuts and engravings are reproductions of line drawings, so that although we may admire and often marvel at the technical ability of the engraver, the credit for what artistic merit such ill.u.s.trations may possess must, in the majority of cases, go to the draughtsman.

The work of the earlier wood engravers may be conveniently studied in _A Lyttel Booke of Nonsense_, by R. D., London, 1912. (See also the relevant works cited under Literature, p. 94).

Bewick, of course, is an outstanding example of an artist who used wood engraving for ill.u.s.trating natural history; the methods he pursued may be studied in the tailpiece on p. 11, which was printed from an electrotype of the original block.

Wood engraving, up to quite recent times, was the method of reproducing text figures; not only for scientific books and periodicals, but also for general literature and journals.

Much of this work is of outstanding excellence; for scientific work the following may be studied:

Duchartre: _Elements de Botanique_. Paris, 1867. The drawings were made by Riocreux and engraved by Leblanc.

Baillon: _Histoire des Plantes_, Paris, 1887. This work contains some beautiful wood engravings, reproductions of drawings by f.a.guet.

Bentham: _Handbook of the British Flora_, London, 1865. The engravings are from drawings by W. H. Fitch.

Deschanel: _Natural Philosophy_, London, 1890. The engravings, many of which are of excellent quality, are by Laplante, Rapine and others. In many cases, notably in the representation of the rays of light pa.s.sing through lenses and also in the ill.u.s.trations of snow crystals, the use of the white line is admirably demonstrated.

Kerner: _Pflanzenleben_, Leipzig, 1888. This contains some excellent engravings by Winkler and others.

Le Maout et Decaisne; _Traite general de Botanique_, Paris, 1876. This work contains splendid examples by Riocreux and Steinheil (see Fig. 8).

Oliver: _First Book of Indian Botany_, London, 1869. This contains some characteristic work of W. H. Fitch.

It does not appear to be generally known that excellent reproductions in colour may be obtained from wood blocks by superposed printing in a manner comparable to that followed in chromolithography although, of course, in the present instance, the blocks are in relief (Fig. 1).

From the foregoing account it is obvious that the engraving even of a small ill.u.s.tration, except it be in mere outline, involves a considerable amount of labour; in fact, if the subject were large it was usual to cut it up into areas and distribute between several engravers, the finished blocks finally being joined together to make the block of the whole picture. Hence it is not surprising to find that when the photo-mechanical processes were perfected, the older methods of reproduction were ousted by the newer, more especially since they are much less expensive; these, therefore, may next be considered.

THE HALF TONE PROCESS.--For the making of a relief block by photo-mechanical means, the main difficulty is the proper rendition of the tones intermediate between black and white; this has been solved, at any rate in part, by the discovery of the half-tone process.

If an ordinary photographic negative be highly magnified, it will be seen that the high lights, the low lights, and the intermediate tones are made by the varying density of the reduced silver. In the lighter parts the small black particles are surrounded by colourless areas, whilst in the dark regions small colourless patches are surrounded by black areas owing to the closeness of the particles of silver (Plate 5, Fig. 2).

What is required, therefore, is a relief block which will print a number of dots of equal density but of unequal size. Verva.s.ser ill.u.s.trates the point in an ingenious way: a plate, covered with a number of cones, is supposed to be acted upon by light in such a way that the cones are truncated in varying degrees according to intensity of the light falling upon them. The section of such a plate would therefore shew a curve (Fig. 3); now if the truncated cones be brought down to one level and a print taken from them, the high lights would be represented by black dots surrounded by white areas and so on.

[Ill.u.s.tration: Fig. 3]

This ill.u.s.trates the principle which obtains in the making of half-tones in which the image is made up of a large number of dots varying in size but all equally dense, so that when viewed from a suitable distance the dots are individually invisible but compose to give gradations of light and shade. In other words, the structure obtaining in a photographic negative is, in a sense, realised by optical chemical means, although the dots in a half-tone block are much coa.r.s.er than those in a negative (Plate 5, Fig. 3).

This result is obtained by interposing between the diaphragm of the camera and the negative--for the half-tone process is a photo-mechanical one--a gla.s.s screen covered with intersecting engraved lines (Fig. 4). As a matter of fact, each screen consists of two plates of gla.s.s similarly ruled and cemented face to face so that the lines intersect.

[Ill.u.s.tration: Fig. 4]

It may at first be thought that the effect of such a screen placed in front of the negative would be to produce merely a cross hatching on the reproduction; this, however, is not the case; if the screen be placed in a proper position relative to the negative and the size of the diaphragm of the camera, the picture will be reproduced in a series of dots of varying size.

The optical and other reasons for this phenomenon must be sought elsewhere,[A] but the following brief consideration will serve to ill.u.s.trate what happens. The rays of light which ultimately reach the sensitive plate are acted upon by two lenses, that of the camera and the meshes of the screen, each one of which acts as a lens on the principle of the pin-hole camera. Each mesh, therefore, brings the image of the diaphragm to a focus on the negative, but the lens of the camera focusses the picture as a whole, thus the amount of light falling on the different pin-holes will vary in intensity, and hence the dots produced will vary in size, for it is a.s.sumed, with good reason, that each dot is built up from its centre and radially expands according to the amount of light acting upon it.

[Footnote A: See Verfa.s.ser, _loc. cit._, p. 94.]

It is obvious that the quality of the resulting picture will depend, other things being equal, upon the coa.r.s.eness of the screen employed.

Screens are ruled with lines varying from 50 to 400 to the inch: the lower rulings give very coa.r.s.e reproductions, and are only used for posters, whilst the higher rulings yield very fine impressions and are employed only for the best work. It is hardly necessary to remark that the finer the screen the better must be the skill of the printer.

To ill.u.s.trate the difference in the results obtained by the use of different screens, the two figures on Plate 6 have been prepared; both were made from the same negative, but for the upper figure a 100-line screen was used, and for the lower a 200-line screen. It will be observed that there is more contrast in the former, and more detail in the latter. Authors should therefore mention when sending in their original pictures the qualities they require in the reproduction; it must, however, be remembered that the blocks made from the finer ruled screens will not print satisfactorily except on more or less highly glazed paper, to the use of the "art" varieties of which there are objections on aesthetic and other grounds.

[Ill.u.s.tration: PLATE 6. Half Tone reproduction of a photograph by Mr.

W. Rowan.

Part of a shingle beach shewing plants of Sea Blite (_Suaeda fruticosa_) and a ring plover's nest with four eggs.]

Before pa.s.sing on it may be mentioned that screens with patterns other than that represented in Fig. 4 are sometimes employed; for instance, the wavy-line screen gives the impression of coa.r.s.e collotype.