The paper used is a very important matter, the selection of which can be safely left to the lithographer, provided he be a good one, unless the author possesses the necessary technical knowledge. If a smooth paper is required, and the paper is not to be damped before printing, India paper is best and plate paper next best. All coarse or grained papers must be damped before printing.
As has already been remarked, lithography is a good process for scientific work; but, unfortunately, considering the number of lithographic plates published, really first-class examples are rare. This is largely due to the original draughtsman; it is unreasonable to expect a lithographer, in all probability ignorant of the subject of the plate, to turn out first-class reproductions of drawings which are obviously bad. On the other hand, lithographers vary greatly in their capabilities, and indifferent plates may be entirely due to their ability not being first rate.
As drawings have to be traced, mistakes are apt to occur; the proofs should, therefore, be carefully examined, for a certain amount of correction can be made on the stone.
The following works contain excellent lithographs, which should be studied by those interested in the subject.
Bornet et Thuret:Notes Algologiques. Paris, 1876-1880. This contains some of the best work, illustrative of science, known to the present author. The original drawings mostly were made by Bornet, and the lithography was carried out by Riocreux—one of the best if not the greatest of botanical artists—Arnoul, Picart and Pierre.Davis and Thurnam:Crania Britannica. London, 1865.Mirbel:Sur le Cambium, Paris, 1842. The plates provide excellent examples of ink lithography by Laplante.Von Mohl:Schriften botanischen Inhalts. Tübingen, 1845. Good examples by Federer.
Bornet et Thuret:Notes Algologiques. Paris, 1876-1880. This contains some of the best work, illustrative of science, known to the present author. The original drawings mostly were made by Bornet, and the lithography was carried out by Riocreux—one of the best if not the greatest of botanical artists—Arnoul, Picart and Pierre.
Davis and Thurnam:Crania Britannica. London, 1865.
Mirbel:Sur le Cambium, Paris, 1842. The plates provide excellent examples of ink lithography by Laplante.
Von Mohl:Schriften botanischen Inhalts. Tübingen, 1845. Good examples by Federer.
The first volumes of theAnnales des Sciences Naturelles(Paris) may be referred to for lithographic work earlier than the above (1820).
For more modern examples the following may be consulted:
Blackman and Welsford:Fertilisation in Lilium, Annals of Botany, Vol. 27, 1913.Gravis:Recherches anatomiques sur les organes végétatifs de l'Urtica Dioica, Bruxelles, 1885. This memoir contains both good and indifferent plates.Keibel:Normentafeln zu Entwicklungsgeschichte der Wirbeltiere, Jena, 1904.Reed:A Study of the Enzyme-secreting Cells in the Seedlings of Zea Mais and Phœnix dactylifera. Annals of Botany, Vol. 18, 1904.Semon:Zoologische Forschungsreisen in Australien, Jena, 1904.Vaizey:On the Morphology of the Sporophyte of Splachnum luteum, Annals of Botany, Vol. 5, 1890.Woodburn:Spermatogenesis in Blasia pusilla, Annals of Botany, Vol. 27, 1913.
Blackman and Welsford:Fertilisation in Lilium, Annals of Botany, Vol. 27, 1913.
Gravis:Recherches anatomiques sur les organes végétatifs de l'Urtica Dioica, Bruxelles, 1885. This memoir contains both good and indifferent plates.
Keibel:Normentafeln zu Entwicklungsgeschichte der Wirbeltiere, Jena, 1904.
Reed:A Study of the Enzyme-secreting Cells in the Seedlings of Zea Mais and Phœnix dactylifera. Annals of Botany, Vol. 18, 1904.
Semon:Zoologische Forschungsreisen in Australien, Jena, 1904.
Vaizey:On the Morphology of the Sporophyte of Splachnum luteum, Annals of Botany, Vol. 5, 1890.
Woodburn:Spermatogenesis in Blasia pusilla, Annals of Botany, Vol. 27, 1913.
Several memoirs in theFauna und Flora des Golfes von Neapel(Berlin) are illustrated by excellent lithographic plates. Many good examples of chromolithography also will be found there.
CHROMOLITHOGRAPHY.Lithography is much used for the reproduction of coloured pictures and illustrations, the process being termed chromolithography. The principles involved are the same as for ordinary work, but it is necessary to print from several stones, one for each colour. It is obvious that much skill is required, for the employment of different colours willgive a large number of secondary and tertiary tints when printed one above the other in various combinations. Thus, by printing part of a design in yellow and the other part in blue, the finished product would show three colours—yellow, green and blue, and by the use of three primary colours a large number of different tints may be obtained.
As already mentioned, each colour is printed by a separate stone, there is thus no limit—excepting that of expense—to the number of different colours which can be obtained.
In practice it is usual to make an outline of the essential parts of the composition on a stone, known as the keystone, which is not necessarily used in printing the picture. An impression of this outline is taken upon a sheet of paper, which is used to transfer the design on to the stones, on each of which the artist will draw only those parts which he desires to be printed in one particular pigment.
Although the sequence of colours is generally blue, red and yellow, it is obvious that various changes in this order must be made according to the colours used and the exact tint required. For instance, a body colour such as cadmium yellow would precede a glaze such as madder-lake; again, two distinct tints may be obtained from red and blue, for example, according to the order of printing—red upon blue will give a mauve, whilst blue upon red will give a purple.
A knowledge of pigments is thus all important, and in printing, the superposition must be perfect.
Plate 2 is an example of a chromolithograph. Miss O. Johnston first drew the outline of the plant, which was phototransferred on to the stone. An impression was then pulled and tinted by the artist, and from this tinted impression the colour stones were made by the lithographer. It may be added that only three colours were used in printing the plate.
Examples:
Baur:Einführung in die experimentelle Vererbungslehre(Plate 1). Berlin, 1911.Bruce and others:A Note on the Occurrence of a Trypanosome in the African Elephant. Proceedings of the Royal Society of London, B. Vol. 81, 1909.Cropper:The Development of a Parasite of Earthworms.Id.Vol. 85, 1912.Oliver:On Sarcodes sanguinea. Annals of Botany, Vol. 4, 1889-1891.Rubbel:UEber Perlen... Zoologische Jahrbuecher, Vol. 32, 1911-12.Biometrika, 1906-7, Vol. 5, Plate 23.
Baur:Einführung in die experimentelle Vererbungslehre(Plate 1). Berlin, 1911.
Bruce and others:A Note on the Occurrence of a Trypanosome in the African Elephant. Proceedings of the Royal Society of London, B. Vol. 81, 1909.
Cropper:The Development of a Parasite of Earthworms.Id.Vol. 85, 1912.
Oliver:On Sarcodes sanguinea. Annals of Botany, Vol. 4, 1889-1891.
Rubbel:UEber Perlen... Zoologische Jahrbuecher, Vol. 32, 1911-12.
Biometrika, 1906-7, Vol. 5, Plate 23.
Mention has been made of the value of a knowledge of colours. The subject is much too extensive to be considered adequately on the present occasion even if it were desirable; its importance, however, warrants a few passing remarks.*
*See Ridgway:Color Standards and Color Nomenclature.
No two people will describe in the same way the colour of, say, a rose petal; both will have a different conception of the colour "crimson." The majority have but a limited sense of colour, and even when this faculty is possessed, the personal equation looms large; further, the ordinary names of colours are quite inadequate for descriptive purposes. For these reasons the importance of a scientific system of colour nomenclature and colour standards is all important. By the use of such a scheme, the exact colour of an object can be found by comparison with an adequate chart, and the name there given will convey to others exactly what colour is described or desired. The plumage of a bird or the colour of a flower can thus be described correctly, and an author can indicate exactly the colour desired in certain parts of a chromolithograph or other reproduction in colour.
Plate 2. Geranium Columbinum.Plate 2.—Geranium Columbinum.A chromolithographic reproduction of a drawing by Miss O. Johnston
A chromolithographic reproduction of a drawing by Miss O. Johnston
PHOTOLITHOGRAPHIC PROCESSES.—Of these methods of reproduction there are several, their value lying in the fact that the originals can be reduced or enlarged with the greatest of ease. The general principles are as follows.
A photographic negative is taken of the original drawing and a positive made on a film of bichromate gelatine. Wherever light reaches the film, the gelatine is rendered more or less insoluble according to the intensity of the light acting upon it; through the dark parts of the negative but little light will pass, so that the gelatine will remain soluble.
The exposure of the positive having been made, the film, which may be mounted on paper, is inked with lithographic ink in the dark room and then washed. The pigment will adhere to those parts acted on by light, but will wash away from those regions unacted upon; obviously the half-tones will retain ink in direct proportion to their density.
The developed positive is then transferred to a stone or zinc plate and impressions taken as in pure lithography for the dark parts are resistant to water and will take the ink, whilst the high lights will retain water and so will not be inked. The intermediate tones will take the pigment according to their density.
In distinction to the previous methods, corrections cannot be made except in so far as the negative can be touched up.
COLLOTYPE.—Of the various photolithographic methods which have from time to time been employed, collotype is the one in most general use at the present time, especially for the reproduction of photographs.
Collotype is a simple process which does not require so extensive a technical knowledge and ability as some of those previously described. But notwithstanding this,the results are sometimes unsatisfactory and unequal; faults due to indifferent originals and to unsatisfactory conditions obtaining in the work rooms. The great drawbacks to good collotype are cold and dampness, and it is for these reasons that continental firms, blessed with a more stable climate, often produce much the best work. Provided the workshops are properly heated, the collotypers of this country ought to be able to turn out good work at all times of the year; indeed, the best firms do.
For this and for other processes in which photographs form the originals to be reproduced, authors should send the negative to the collotyper; if this be impossible, positives of the best possible quality, printed on ordinary P.O.P. paper, toned to various shades of purple, and also on smooth bromide paper, in ordinary black tones, should be provided in order that the collotyper can choose the print he most prefers to work with. Also, it is usual to glaze the prints.
The method is as follows. A piece of british plate glass, about half-an-inch in thickness, is ground on one side with fine emery powder, and then thoroughly washed and dried. The plate is covered with a filtered mixture of the colloids sodium silicate and dextrine or albumin, and placed in a warm oven to dry. If metal plates are used, such as zinc or copper, this preliminary coating is unnecessary; glass plates, however, must have the substratum in order that the sensitised gelatine—which is next put on—may stick.
When the plate is dry, it is thoroughly washed with water in order to remove any free silicate; it is then dried and put away until required for use.
The sensitising solution is made up of gelatine and bichromate of potash dissolved in water; before use it is filtered, freed from air bubbles and heated to not more than 120° F. The plate is now placed on a stand, whichis provided with levelling screws, in the oven, and, when the temperature has reached 120° F., an amount of the bichromate gelatine solution sufficient to make a thickness of film proper for the mode of printing to be employed is poured upon the plate.
The oven is kept at a constant temperature, 120° F., until the gelatine is dry, when it is allowed to cool gradually.
Whilst the gelatine is setting, precautions against vibration must be taken else the plate will be spoilt.
When dry, the collotype plate is sensitive to light and moisture; its surface shows a more or less regular series of convolutions which resemble those of the outer surface of the human brain, although, of course, very much smaller. The character of the grain is very important, for if it be too fine it will not take up a sufficiency of ink, and, on the other hand, if too coarse it will yield coarse impressions.
A reversed negative, of a quality beyond reproach, must be made of the original; if the subject is dark or has heavy shadows the negative is frequently slightly over exposed so as to soften them.
The collotype plate is then exposed under the negative and washed in cold water until the yellow bichromate no longer comes away. It is then dried.
In printing, the plate is damped and rolled up with ink as in lithographic printing; the amount of ink adhering to the film depends on the extent to which the different parts have been acted on by the light, as has already been mentioned. The moistening of the plate—mis-termed etching—is best done with dilute glycerine containing 75 per cent. of water, which when first applied should be allowed to remain on for about half-an-hour. The excess of moisture is taken up with a sponge or a ball of rag, and then the plate is inked and printed in a lithographic or a collotype press. The picture is usually masked with tin foil in order that its edges may be quite clean.
Of the faults which may occur, the following may be alluded to. A mottled appearance may obtain in the high lights; this is due to the coating of gelatine being too thick. More commonly, the reproductions may appear flat owing to the degradation of the high lights; this is a sign that the sensitive film has been acted upon by moisture during its critical existence between the drying and the washing out of the potassium bichromate, or that the temperature has been too low.
The following contain good examples of collotype.
Karsten and Schenck:Vegetationsbilder, Jena.Oliver:Notes on Trigonocarpus and Polylophospermum. New Phytologist, Vol. 3, 1904.Semon:Zoologische Forschungsreisen in Australien. Jena. 1912.Thompson:The Anatomy and Relationships of the Gnetales. Annals of Botany, Vol. 26, 1912.See also Plates 3, 4, 5 and 9 in the present work.
Karsten and Schenck:Vegetationsbilder, Jena.
Oliver:Notes on Trigonocarpus and Polylophospermum. New Phytologist, Vol. 3, 1904.
Semon:Zoologische Forschungsreisen in Australien. Jena. 1912.
Thompson:The Anatomy and Relationships of the Gnetales. Annals of Botany, Vol. 26, 1912.
See also Plates 3, 4, 5 and 9 in the present work.
THE PREPARATION OF ILLUSTRATED PAGES.Of the processes dealt with, photogravure lithography and collotype are those most generally used at the present day for the printing of plates or insets. Half-tone also is employed, a process which will be considered later since it is essentially relief printing. This, therefore, is a convenient opportunity to make a few general observations on plates.
Plates should only be employed for the reproduction of subjects of such complexity that cannot be reproduced satisfactorily by figures in the text.
A plate or page made up of several illustrations should look well as a whole; in other words, it should not outrage all the canons of composition, it should have some pictorial effect. At the same time, for facility of reference, the individual figures should run in a convenient sequence.This latter point is so important that a plate composed really well is distinctly rare, for a compromise nearly always has to be made. At the same time there are, apparently, comparatively few authors who pay much attention to plate design.
Although it is not desired to write of the laws of pictorial composition, attention may be drawn to a few points which are amongst those generally neglected.
The figures should not be crowded together; a reasonable amount of margin should be left around each. They should be arranged, as far as possible, in such a way that a sense of balance is maintained. As to how this is to be accomplished will depend upon the nature of the illustrations; if they are all about equal in tone, the largest ones should preponderate towards the base of the plate, and notvice versâ. The difference which this makes will be obvious if the two accompanying illustrations (Figs. 1 and 2, Plate 3) be compared. The first is a reduced copy of the plate as it was published: it will be noticed that it has a top-heavy appearance, which is corrected in the second figure by the simple device of turning it upside down.
Plate 3. 1Plate 3. - 1
Plate 3. 2Plate 3. - 2
If, on the other hand, the figures are some lighter and others darker, the latter should form the base, since low tones give the idea of solidity; this is so marked that in cases where the figures vary much in size and tone, the darker ones may nearly always be situated at the base or at any rate low down on the plate unless they are very much smaller than the lighter toned ones.*
*If, of course, the reader understands chiaroscuro, he will take no notice of this paragraph, but arrange his plates in accordance with his ability.
An examination of the figures on Plates 4 and 5 will roughly illustrate these points. The upper figure of Plate 4 is well designed, and no improvement could be made, bearing in mind the compromise alluded to above. The lower figure is, however, not so good, it wasobviously a difficult one to arrange; it would have been improved if Figs. 23, 26 and 28 could have been placed in the top tier, but this would have seriously disturbed the sequence. The first illustration on Plate 5 is well designed; it would, however, have been improved by interchanging 8A and 11B.
Plate 4. 1Plate 4. - 1
Plate 4. 2Plate 4. - 2
Plate 5. 1Plate 5. - 1
Plate 5. 2Plate 5. - 2
Plate 5. 3Plate 5. - 3
We may now pass on to the individual figures; these should shew the essential features, together with some surrounding and comparatively extraneous matter; often there is included too much of unimportance and its retention means a waste of valuable space. The first thing to do, therefore, is to trim, if needs be, the figures; their shape is more or less immaterial, provided that in cases where there are a large number of illustrations on one plate, they are not all alike. The American fashion of circular figures is particularly displeasing, at any rate to the author.
Having trimmed the figures, the next point to decide is whether any require reduction; if they do, cut out pieces of paper (referred to as patterns below) of the size which the figures will ultimately appear: on the whole, it is better to avoid reduction of the originals, for without a good deal of experience it is very difficult to judge exactly what the result will be; a good idea, however, may be gained by the use of a diminishing glass.
The size of the available surface of the plate should now be ruled on a white sheet of fairly thick cardboard, and the figures, or their patterns, arranged so as to be easy of reference, to compose as well as may be, and spaced in such a way that, in the case of a quarto plate to be folded vertically, no figure is placed so that the fold will pass through its centre. Nothing is more irritating than having an illustration spoilt in this way.
All this may be done by arranging in different waysuntil a satisfactory result is obtained, a process which may take an hour or two. The figures should then be pasted down, covered with several sheets of blotting paper and placed in a press. A press is seldom available; when such is the case, a number of heavy books serve equally well.
The lettering must next be attended to. The individual figures are usually designated by numbers; this is a bad method, since it involves referring to the description of the plate. The best way is to use a number, and after it to add the name of the plant or animal, and, if needs be, a description as short as may be. If the author can "print" or write reasonably well, well and good; if not, it is better to attach a slip to the plate with full directions relating to lettering, and to write in pencil on the plate the titles, etc., required in the proper places for the guidance of the craftsman. The typewriter is sometimes employed for this purpose by authors; it is purely a matter of taste, but some readers feel a slight shock when this method is resorted to.
In some cases a key to the plate printed on tough translucent tissue paper and having the necessary information, guide lines, etc., is inserted with the plate.*
*See Kerner and Oliver:Natural History of Plants(First Edition) London, 1894.
In the case of glossy chromolithographs this practice is best avoided, for the key is apt to stick to the plate if too much pressure is used when the book is bound.
With regard to the "catch letters" used to indicate different parts: these should be as obvious as possible, and the guide lines should be either in black or in white ink, according to the general tone of the illustration. These lines should be conspicuous without being heavy. Not infrequently they, together with the lettering, are printed on the plate by a second impression in red ink.
The foregoing is primarily the business of the author; with regard to editors and publishers, all plates should be mounted in a manner to facilitate reference and should be printed on suitable paper; the former is seldom or never done. All plates which must be constantly referred to in reading the text should have a selvedge as broad as the book, so that when unfolded the whole plate is visible, no matter what page is being read. This would, no doubt, prove an additional expense, but this should not militate against the suggestion here made, not by any means an innovation, for in many cases it would save the expense of mounting on guards, and, further, the additional expenditure could be saved several times over in other ways.
With regard to paper, this generally is satisfactory; unfortunately, highly glazed paper, mis-termed art paper, with an enamelled or chromo surface, and consisting chiefly of china clay and size, is generally used for printing the best half-tone reproductions. For this purpose a paper with a suitable surface, obtained by means other than those mentioned and not too costly, is highly desirable, since art paper has the reputation of being not at all permanent, owing to the deleterious action of moisture, and is somewhat brittle. When used, art paper, if folded, should have a proper paper hinge along the fold.
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.
tailpieceG. Oliver, del.
G. Oliver, del.
Fig. 1Little maid, little maid,Whither goest thou?Down in the meadowTo milk my cow.Fig. 1.—A wood engraving, by Edmund Evans, fromthe original drawing by Kate Greenaway.Reproduced by permission of the publishers, Fredk. Warne & Co.
Little maid, little maid,
Whither goest thou?
Down in the meadow
To milk my cow.
Fig. 1.—A wood engraving, by Edmund Evans, fromthe original drawing by Kate Greenaway.
Reproduced by permission of the publishers, Fredk. Warne & Co.
INorder that illustrations 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-illustrations, so that this method may next be considered.*
*See Treviranus, C.L.:Die Anwendung des Holtzschnitts zur bildlichen Darstellung von Pflanzen. Leipzig, 1855.
WOOD CUTS AND ENGRAVINGS.The invention of illustrating 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 illustration; 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 illustrated 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.
Fig. 2Fig. 2.
In fact, the cut illustrates 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 space which is similarly obtained; and the black space, 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 illustrates 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 illustrations may possess must, in the majority of cases, go to the draughtsman.
The work of the earlier wood engravers may be conveniently studied inA 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 illustrating 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:Eléments 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 Faguet.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 passing through lenses and also in the illustrations 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;Traité général 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.
Duchartre:Eléments 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 Faguet.
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 passing through lenses and also in the illustrations 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;Traité général 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 illustration, 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 surprisingto 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. Vervasser illustrates 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.
Fig. 3Fig. 3
This illustrates the principle which obtains in themaking 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 coarser 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 glass screen covered with intersecting engraved lines (Fig. 4). As a matter of fact, each screen consists of two plates of glass similarly ruled and cemented face to face so that the lines intersect.
Fig. 4Fig. 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 phenomenonmust be sought elsewhere,* but the following brief consideration will serve to illustrate 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 assumed, with good reason, that each dot is built up from its centre and radially expands according to the amount of light acting upon it.
*See Verfasser,loc. cit., p. 94.
It is obvious that the quality of the resulting picture will depend, other things being equal, upon the coarseness of the screen employed. Screens are ruled with lines varying from 50 to 400 to the inch: the lower rulings give very coarse 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 illustrate 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 æsthetic and other grounds.
Plate 6. 1Plate 6. - 1
Plate 6. 2Plate 6. - 2Half 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.
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 passing 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 coarse collotype.
The preparation of the blocks may now be briefly dealt with.
A negative of the picture, using a screen suitable for the purpose, is taken on a special dry gelatine plate ("process" plates) or on some other form of negative,e.g., wet collodion which is most commonly employed. This negative requires very careful development in order to get the dots right.
From the negative a positive is made upon a copper or zinc plate, suitably coated with a sensitive film. The usual practice is to coat the polished metal plate with a mixture of water, albumen, fish glue, ammonium bichromate, chromic acid and ammonia; the plate is then dried and, when cooled, exposed under the negative. The action of the light on such a film, the essentials of which are the albumen, the glue or gelatine and a chromate, has already been described. The mixture becomes more or less insoluble in water, according to the intensity of the light falling upon it.
The positive is now rinsed in water, and is sometimes stained with an aniline dye in order to render the film more visible. Next it is developed in a stream of water until the surface of the metal is visible between the dots, the last traces of the soluble gelatine being removed with warm water. After drying, the plate is evenly heated over a Bunsen burner until the dots of gelatine mixture turn chocolate colour, when the plate is allowed to cool gradually. This is known as burning in. The plate, if necessary, is now touched up and the back, sides and margins varnished in order to protect them from theacid: when the varnish is dry, the plate is etched in a weak solution (about 2½ per cent.) of nitric acid if the metal be zinc; if the plate be copper, it is usually etched with a solution of iron perchloride.
On taking a proof, there is almost certain to be a lack of contrast, the plate is then fine etched, by which means a considerable improvement can be made; and, by covering certain parts with an acid-resisting substance ("stopping out"), it is possible to fine etch locally.
Incidentally it may be mentioned that machine etching, by which a fine spray of the etching fluid is distributed over the plate, has recently come into vogue, for it is claimed that the results print better and are in other ways an improvement upon the older method.
The plate may now pass through the hands of an engraver, who removes any blemishes, as far as is possible, improves the high lights, and so on; in fact, a skilful engraver can improve the plate considerably.
After the plate is trimmed, and the superfluous metal cut out by means of a routing machine, it is firmly tacked to a wooden mount, usually of oak, but sometimes of mahogany, especially if the plate is large. In order to obtain the best results, the printing, in a typographical machine, should be done on highly calendered paper—so-called "art" paper; in fact, this is absolutely essential if a fine screen has been used; it is only the blocks made with the coarser screens that will give fair prints on ordinary paper. For this reason reproductions made by the half-tone process are very generally treated as plates unless the glazed paper is used throughout the book. The process is used principally for the reproduction of photographs, and for pencil or wash drawings.
With regard to photographs, it has already been mentioned that authors should send the negative or two or three prints differently toned, in order that the operator can choose the one most likely to give the best result.
It is sometimes difficult in a photograph of a landscape to obtain a negative in which the particular feature it is desired to represent—e.g., in photographs of vegetation—stands out with the requisite contrast. This is due to the position of the sun at the time of exposure, or to the use of ordinary plates. The remedy for the first is to take the photograph when the proper light obtains; with regard to the second, the use of colour correct plates, together with a colour screen in front of the lens, will obviate the defect. Since for scientific purposes the correct interpretation of the various tones of the vegetation, for example, may not be essential, variously coloured screens may be used in order to emphasise a particular feature. For instance, it will be noticed how well the bushes in Plate 7 stand out. This effect was obtained by the use of a panchromatic plate in conjunction with a red colour screen.
Plate 7Plate 7.—Half Tone reproductionof a photograph taken by Dr. Mees through a red screen.
of a photograph taken by Dr. Mees through a red screen.
With regard to drawings in wash, charcoal or pencil, in which there are half-tones; these are better drawn on an enlarged scale, especially if the author is not a skilled draughtsman, for improper gradations in shading and other imperfections will not appear so noticeable in the reduced reproduction. Originals should all be made in one colour; in the case of wash drawings, diluted Indian ink (really Chinese ink) will give excellent results.
In making pencil drawings, a fairly stout hand-made paper with not too much grain should be used. If the drawing is to be of some size, the paper may be damped and pasted by its edges on to the drawing board, it will then be stretched quite flat and will not cockle when dry.
The outline of the object may first be sketched in lightly with a soft pencil and then the shading may be proceeded with. To do this, broad-pointed soft pencils, 2 B, 3 B, or 4 B, should be used, and it is better generally to work from the high lights to the shadows. To avoid rubbing finished parts, the work should proceed from thetop of the board downwards, especially in the case of large drawings.
In order to obtain a nice gradation and a more smooth appearance—more especially when a very coarse paper has been used—the work may be gone over with paper stumps of appropriate size and softness, and, of course, India rubber may be employed where it is desired to reduce the density of the shading.
When finished, the edges of the various parts may appear woolly owing to the rubbing of the lead; this may be cured by cleaning up the edges with a trimmed piece of India rubber, but in so doing there is always a risk of rubbing out part of the shading, especially if the outline be at all intricate. If preferred, all the shaded parts may be fixed by painting them over with a suitable solution, gelatine for instance, paying particular attention in following the correct outline. When dry, the application of soft india-rubber will soon clean up the blurred edges.
If charcoal be used the same procedure may be followed. Charcoal and pencil drawings should be fixed, in order to prevent rubbing, before sending to the block makers. A suitable fixative may be purchased or one may be made by dissolving white resin in alcohol and applying it to the paper by means of a scent spray or an atomizer. A very good fixative may be made by dissolving a little gelatine in hot water and applying it whilst hot by means of a broad, flat camel hair brush, or ordinary milk may be used in a similar way. After the fixative has been put on, the drawing should be pinned up by one corner—unless, of course, it was pinned up before the fixative was employed, which is the best way when the fixative is an alcoholic solution—and allowed to dry; it may then be placed under pressure in order to flatten it, for fixed drawings generally shew a tendency to curl, especiallywhen the preparation used for fixing has only been applied to one surface of the paper.
In making drawings for reproduction by means of the half-tone process, there are a few general points to which attention should be paid.
It should be remembered that there is not infrequently a tendency towards flatness in the reproduction; it is therefore important that the originals should be "plucky," and, on the whole, it is better to exaggerate with regard to high light and shade, especially if there is much modelling or perspective.
Finally, with regard to lighting, it is better for the majority in drawing their objects—solid objects in relief are referred to—to use a more or less lateral illumination and to represent only the high lights, shades and shadows referable to this main direction of illumination. A high relief will thus be obtained, and the effect will prove more satisfactory than if minor sources of illumination are unsuccessfully dealt with. This is especially important in drawing complicated structures such as models of vascular tissues, embryos, etc.
In cases where many such figures are to occur on one page, it is highly desirable that the lighting of each should be from the same direction.
The use of the half-tone block is now almost universal, so that it is hardly necessary to mention examples, more especially as they are hard to judge without seeing the original picture. Those in the present book are all of a high quality. Excellent examples will also be found in Tansley'sTypes of British Vegetation(Cambridge, 1911) and in theJournal of the Royal Horticultural Society.
Proofs should be carefully compared with the originals, particular attention being paid to the rendering of the tones; as already remarked, fine etching will clear up a block and will often prove a remedy to flatness.