Chapter II: Part 2

All this may be done by arranging in different ways until 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.[A]

[Footnote A: 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.

RELIEF PRINTING

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 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.[A]

[Footnote A: 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.

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 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 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: _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 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; _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 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 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. 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.

This illustrates 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 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.

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 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.

[Footnote A: 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 aesthetic and other grounds.

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 the acid: when the varnish is dry, the plate is etched in a weak solution (about 2-1/2 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.

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 the top 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, especially when 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's _Types of British Vegetation_ (Cambridge, 1911) and in the _Journal 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.

An author will naturally consider whether a photograph is to be reproduced by means of photogravure, collotype or half-tone. It is impossible to lay down any laws on the subject, but the following points should be considered.

If it is essential to have the reproduction in the text, a half-tone block must be used; it must, however, be remembered that the paper used for the letterpress may be very unsuited for the printing of half-tones. On the other hand, if it be immaterial where the picture is placed, then the relative merits of photogravure, collotype and kindred processes and half-tone must be weighed.

Provided that expense need not be considered, photogravure will, in the majority of cases, give the best results; on the other hand, if this process is too costly, then the choice lies between collotype and half-tone. The latter method will often give a result with more contrast as compared with collotype, whilst collotype will give a truer interpretation of the tones.

As has already been remarked, the best results with half-tone blocks only are to be obtained by the employment of a paper which seemingly has no lasting qualities; it therefore follows that if the reproduction forms an important record, the use of collotype is indicated, since many varieties of good paper are available. As a general rule photo-micrographs are best reproduced by collotype.

In order that the respective qualities of these three processes--photogravure, collotype and half-tone--may be compared, Plates 8, 9, and 10 have been made from the same photograph, a view taken by Dr. F. F. Blackman of the Bouche d'Erquy, a salt marsh in Brittany, which was selected chiefly on account of the large number of tones it contains.

These three plates are not entirely comparable, since the heavy shadows in the right hand bottom portion of the photogravure have been touched up by the engraver. This was not intended by the author, but the plate was retained as it shews that directions regarding this point should not be omitted when sending the drawing or photograph to be reproduced. It also indicates that for critical work, when an exact a facsimile as possible is required, collotype should be used, for the plate cannot be touched up.

With regard to the reproduction of drawings shaded by means of wash or pencil, the same remarks apply, with the addition that if it be possible to express what is desired by other means, suitable for reproduction by line block, these latter should be employed. To illustrate this point, Figures 5, 6, and Plate 11 have been inserted; all illustrate the vascular skeleton of a fern (_Marattia fraxinea_), the first one is in outline and the second is shaded by lines of varying thickness; both of these are reproduced by means of the line block, whilst the third is a reproduction by half-tone of a pencil-shaded drawing. In order to obtain a fair comparison, the half-tone is reproduced as a plate, owing to the fact that it would not print satisfactorily on the paper used for the letterpress.

THE HALF-TONE THREE COLOUR PROCESS.--This process is much used for colour reproductions of various subjects; and, in view of the fact that the best results can only be obtained by the best photography, the object should, if possible, be sent to specialists for reproduction. In many cases, however, this is impossible, _e.g._, landscapes and animal and plant portraits amidst their natural surroundings, so that the scientist, if unable to make a water colour drawing, which will give by far the best result, must make his own negatives.

The first thing to do is to purchase a set of colour-filters, adapted to the colour-correct plates to be used, from firms who specialize in these matters, Messrs. Paget or Messrs. Wratten for instance, and from them the inexperienced should obtain full information regarding exposure, etc., for it is essential that the exposure of the negatives should be correlated in order that all may have the same tone-value.

The colour-screens, blue, green and orange, are made by dyeing gelatine with suitable stains; the films are stuck on to perfectly plane glass and are mounted in frames. In practice these screens are usually placed behind the lens, in which case a special camera is necessary, or they may be adapted to fit on to the front of the lens. In either case the procedure is the same; three negatives are taken one after the other through each colour filter, the exposure being modified in order that the tones in each case may be of equal value.

There are thus obtained three negatives which, of course, yield positives which look very different one from the other. These prints may be sent to the block makers, but it is better, on the whole, to send the negatives with clear indications as to the colour of each.

From each negative there is made by contact a transparency, and from these positives there are prepared a set of half-tone negatives from which are made the half-tone blocks.

The reproductions are made by superposed printing of the three blocks, yellow being printed first, then red, and finally blue (Plate 12).

As indicated above, it is hardly worth while to make negatives for this process unless the operator is a really skilful or at least an efficient photographer, and even then the final product may prove unsatisfactory.

Better results are generally to be obtained by sending to the block maker a Lumiere colour photograph with full instructions regarding any corrections in the colours which may be necessary.

Examples:--

Bateson: _Mendel's Principles of Heredity_, Cambridge, 1909. Church: _Types of Floral Mechanism_, Oxford, 1908. Seward: _Darwin and Modern Science_, Cambridge, 1909.

PHOTO-MECHANICAL LINE BLOCKS.--The photo-mechanical line block, commonly known as a zinco, is in a sense the lineal descendant of the wood block. As a means of reproduction the possibilities of line blocks are very great, for not only is it possible to reproduce by their means all kinds of line drawings, but also drawings in charcoal and crayon, provided they be suitably executed on a proper grained surface. In fact, an artist or draughtsman who has a thorough knowledge of the process and its capabilities can obtain extraordinary results. The process has the further advantage of being both quick and inexpensive, a few hours only being required to make the finished product.

Their mode of manufacture is the same in principle as for half-tone blocks; in the case of the latter, the method known as the enamel process was described; in the present instance a different procedure may be dealt with.

A photograph of the drawing is taken on a negative, the wet collodion process being generally followed, although dry process plates may be used.

A highly polished zinc plate is sensitised with bichromate of potash and gelatine, or by other means, and, when dry, is exposed under the negative.

The exposed metal plate is then taken into the dark room and evenly, but thinly, coated with etching ink. When the ink is dry, the plate is developed in water; the unexposed gelatine, and with it, the ink, will come away, its removal being helped by the judicious application of a dabber of wet cotton wool.

The plate may next be "rolled over" with an ink which will more stoutly resist the action of the acid than that used in the first inking, but prior to this it is usual to soak the plate in a mixture of gallic acid, phosphoric acid and gum. This second rolling up must be carried out as if the plate were for lithographic reproduction; and, when dry, powdered resin may be applied, in order to make a better acid-resist, as in the preparation of a lithographic stone.

The plate is now etched slightly in a weak solution of nitric acid; it is then rinsed, dabbed dry and placed upon a hot plate until the resin has stuck well to the ink. When cool, the margins, sides and back are protected from the action of the acid by means of a varnish and the plate is given its first real etch, which is a very slight one. After rinsing and drying, the plate is again heated until the ink and resin have melted and flowed down the exposed sides of the ridges of metal produced in the first etching. This application of ink and resin must be repeated in order that the exposed sides of the ridges may be well covered with the acid-resist and so will not be undercut. The plate is then given its second etch, and this is done with a stronger acid, after which the sides of the lines are again protected with resinous material in the same way as before. The third etch follows, after which the metal is thoroughly cleansed from all the ink, etc.

In order to smooth the shoulders of the lines, the plate is given a finishing etch: the cleaned plate is warmed and rolled up with hard etching ink; the metal is then heated until the ink becomes glazed, and, when cool, is placed in the acid bath for the requisite amount of time. If necessary the plate, after cleaning, is touched up with a graver, and the superfluous metal is cut away. Finally it is mounted on a block of wood, and after the corners and sides have been trimmed square, the block is ready for the press.

To illustrate the enormous improvement which may result from the block passing through the hands of a skilful engraver, two line blocks of a wood engraving by Riocreux (see p. 36) have been prepared. Fig. 7 is the impression given by the block as ordinarily turned out, whilst Fig. 8 is a precisely similar block which has been worked up by an engraver.

There are several other methods of making the blocks, but the principles are the same as in the foregoing process.

In examining the proofs it must be remembered that deletions are not the only alterations that can be made in the finished block; not only can lines be cut away, or their character altered by removing part of the metal from them, but additions can be made in reason. For instance, lines can be added across open spaces, and if part of the printing surface has been accidentally removed in cutting away the superfluous metal, the damage can be made good by building up with solder and working on this with the graver. If, however, the additions required are at all extensive or complicated, it is better to have a new block made.

Inasmuch as scientific illustrations are to describe and explain definite facts, the drawings must needs be materialistic rather than suggestive; in other words, a more or less conventional system must be employed.

In making their drawings for reproduction by line blocks, authors have at their disposal the black line, the white line, the black space, the white space, the black dot and the white dot, all of which may be combined in various ways. No tones, other than black and white, are available; if it be desired to represent half-tones, they must be rendered by the above-mentioned means.

In the majority of cases the originals should be made with black ink on white Bristol board or smooth white paper; ordinary lead pencil drawings on smooth paper are useless, and lead pencil, black crayon or charcoal in combination with grained paper or board should not be employed unless the draughtsman has the requisite skill and knows exactly the limitations of the line block. For all ordinary folk black ink and Bristol board cannot be improved upon.

The drawing may be made first with a soft lead pencil, using the camera lucida or other optical aids to correct delineation. The pencil lines are then gone over with ink; for this purpose a good black ink is necessary. Wolff's Indian ink, Higgins' waterproof ink and Steuber's waterproof drawing ink are highly satisfactory, and there are many others. With regard to pens, a suitable implement is all-important; Gillott's lithographic pens and Brandauer's No. 515 are recommended. For straight lines of an even thickness a ruling pen is very useful, and these may be obtained fitted with an adjustment which enables the worker to rule a line of a definite thickness, _e.g._, .5 mm. and so on.

All drawings should be made larger than it is intended the reproduction to be, for slight inaccuracies, ragged lines, and other blemishes will thus appear less obvious. This drawing on a large scale is often a stumbling block, because the work appears too open and the draughtsman is tempted to put in too much; this must be avoided, else the crowded lines may join together in the reduced reproduction. Also it must be remembered not to draw too finely, else the work in parts may disappear entirely in the reproduction. In drawing on an enlarged scale a certain amount of exaggeration may be employed, in order that when reduced the drawing may not be quite spiritless.

When representing a solid object, such as a plant or an animal, to shew the external morphology, it is to be borne in mind that form is the main thing to represent, and this can be expressed by outline drawing alone. In fact, more or less primitive methods must be employed, and better models cannot be followed than the best wood cuts.

An examination of figures 10 and 12 will shew that Fuchs[A] attained his object by simple outline drawings; he never employed local colour, and shading he used very sparsely indeed, and then only to give expression to the form of some thick part. Fuchs's celandine (Fig. 10) should be compared with the drawing of the same plant (Fig. 9) by R. G. Hatton.

[Footnote A: The methods followed by the illustrators of
the Herbals may be conveniently studied in Hatton's "The
Craftsman's Plant Book," London, 1909, and Arber's "Herbals,"
Cambridge, 1912.]

The methods of Matthiolus (Figs. 11 and 13) were somewhat more advanced, for he used shading not only to express form but also to give a certain amount of relief. It will be noticed that he shaded by lines which followed the moulding of the parts.

The work of Riocreux (Fig. 8) should also be studied; it will be observed that he managed to get a very high relief in his drawings by the simple means of straight or curved lines, according to the shape of the part, of varying thicknesses.

There is no necessity for keeping all the lines of even thickness. For instance, provided the character of the form is not altered, the outline on the shaded side may be made thicker than on the illuminated side; also distance can be indicated by the use of thinner lines, for these, although really black, will give the impression of greyness. Then again, a line may be drawn with local increases and decreases in thickness, as in ordinary writing, and such lines drawn by a skilled hand can be made to express a marvellous amount of modelling.

(From Hatton's _Craftsman's Handbook_.)]

The draughtsman, however, is not restricted to lines; any marks which can be made with a pen and black ink may be employed, provided they be sufficiently firm and large.

The accompanying figure (14) which is a reduction of an illustration in Church's _Floral Mechanisms_, illustrates the use of lines of varying lengths for shading.

In shading, the effect of shadow may be obtained by increasing the thickness of the lines, but they must not be drawn too closely together; on the other hand, the lighter parts can be represented by thinner lines placed further and further apart, and the lightest parts by the white of the paper. Cross hatching may also be employed (see Fig. 15), but the crossed lines must not be too close together, for otherwise they will tend to thicken in the making of the block and so will print too black.

For very delicate shading and tinting, stipple may be employed, but the dots must be quite definite, sufficiently large to stand reduction, and not too close together (Figs. 18, 28c, and 32). A particularly good example of this method will be found in Butler's paper on _Allomyces_ in the Annals of Botany, 1911, vol. 25. Dots have also been employed in Fig. 28c (p. 69).

With regard to local colour; this may be indicated by shading, by a white space, or by a black space.

Hitherto, drawing with black ink on white paper alone has been considered, but the reverse is equally available; much can be expressed by drawing with white ink on black paper.

Drawing in white upon a black ground is not frequently attempted, but an excellent example by Miss Janet Robertson is shewn in figure 16, which is well worthy of study, since it illustrates to a nicety some of the means at the disposal of the draughtsman for line blocks. The black surface is best obtained by the use of a waterproof Indian ink applied with a brush to a white surface, the drawing being made with a dense white ink, using a pen or a brush. The white ink may be made by diluting any good opaque white water-colour paint, or process white may be used. The composition of this should be zinc oxide or baryta, for these do not darken with age; the author once used for this purpose a white pigment which proved excellent at the time; the drawings, however, subsequently turned dark brown owing to the fact that the basis of the paint was apparently a compound of silver.

A line reproduction of a drawing by Miss Janet Robertson.]

The top part of the drawing (Fig. 16), shewing the general morphology of the plant, was drawn with a brush charged with white ink upon a black ground. In the simplest possible way relief has been obtained by representing the leaflets of the nearer fronds by white spaces, whilst those further away are represented by white outlines. An enlargement of a frond is shewn on the lower part of the picture, and here the parts are represented in black on a white ground. The leaflets are in black outline and the fruits are made to stand out, as in the upper part, by the use of local colour--in this instance black--their shape being indicated by the curve of the higher lights. In brief, a very effective drawing has been made by the simplest use of the white line, the white space, the black line and the black space.

(From a drawing by Miss Baker.)]

This may be compared with figure 17, which was drawn by Miss Baker; the method pursued is entirely different to the last, it being a pure pen and ink drawing on white paper. No local colour has been employed, and the modelling has been expressed by the lines used for shading which have been made by short strokes with a fine pen. The result is suggestive of an engraving but this was not intentional; under no circumstances should an attempt be made to imitate in a relief block effects which can only be obtained by intaglio.

From what has been said it is obvious that the photo-mechanical line block can be used for the reproduction of all kinds of drawings in pure black and white; to illustrate this figures 18-26 have been inserted.

A diagrammatic sketch by Mrs. F. E. Fritsch of _Rhizophora conjugata_, a mangrove. (Tansley and Fritsch, _New Phytologist_, 1905, vol. 4.)]

A shoot of _Acanthus ilicifolia_, a mangrove. Drawn by Mrs. F. E. Fritsch. (Tansley and Fritsch, _New Phytologist_, 1905, vol. 4.)]

A longitudinal section of a fossil seed, _Conostoma oblongum_. Drawn by Dr. E. J. Salisbury. (Oliver and Salisbury, _Annals of Botany_, 1911, vol. 25.)]

The Meadowsweet (_Spiraea ulmaria_), shewing four years' growth. (Yapp, _Annals of Botany_, 1912, vol. 26.).]

THE DRAWING OF MICROSCOPIC DETAILS.

Questions relating to the drawing of microscope sections may now be dealt with. Usually these are drawn in pencil and reproduced by means of lithography; this is quite wrong, for in addition to its being an unnecessary expense, it is also an inconvenience to a reader, since the figures are necessarily divorced from the letterpress. There are very few histological details which cannot be represented by line blocks, and with a proper co-operation between the author, the block maker, the printer and the publisher, even the delicacies of karyokinesis could be reproduced in the text.

For demonstration purposes, transverse sections of plant-structures may first be taken.

The walls of the various elements may be represented by lines of more or less equal breadth, but in those cases where the walls are particularly thick, _e.g._, the elements of the wood, the thickening may be represented by an additional line. This is seen in Fig. 27, in which it will be noticed that the middle lamellae of the wood-elements are represented by black lines.

(From Butler's paper on Gummosis of _Prunus_ and _Citrus_. _Annals of Botany_, 1911, Vol. 25).]

This is a particularly good drawing, but, unfortunately, it has been over reduced.

On the other hand, the various tissues may be represented by lines of varying breadths, the thickest walled cells having the same double contour as in the above, but with the addition of local colour in the shape of diagonal shading. This is not uncommonly found in papers dealing with the anatomy of plants by French authors; it is illustrated in Figure 28 _a_. If preferred, such thick-walled elements may be entirely represented by thick black lines as in Figure 28_b_, and when such cells are relatively few in number, this method has much to recommend it since a greater relief is obtained.

_a_

_b_

_c_

A transverse section to shew the vascular cylinder of the root of the spinach, _c_ is somewhat older than _a_ and _b_.]

Finally, an attempt may be made to draw in a more detailed fashion as in Figure 28_c_. Here the thickness of the cells of the wood is represented by broad black lines, the middle lamellae being left white. The lines marking the boundaries of the other cells vary slightly in thickness, but this is to a great extent masked by the representation of the cell contents, which consist entirely of dots in the case of the protoplasm, whilst the nuclei are represented by dark ovals--black relieved with small white areas. By varying the size of the dots and their distance apart, varying densities can be indicated.

It has been mentioned above that it is possible to reproduce fine detail by means of the line block; this is illustrated in Figs. 29 and 30.

Fig. 29, which illustrates a stage in the division of a nucleus, was drawn with black crayon on a rough-grained piece of Whatman's water-colour paper. The cytologist will, doubtless, criticize its coarseness, but it may be mentioned that the roughest paper at hand was designedly employed in order to illustrate the point raised. That a finer grained paper will give more delicate results is shewn by Fig. 30, which is a reproduction of a drawing, kindly lent by Dr. W. G. Ridewood, made with ordinary lead pencil on grained Bristol board. Its delicacy is obvious, and at first sight it could easily be mistaken for a lithograph.[A]

[Footnote A: Many similar examples will be found in Ridewood's
memoir _On the Cranial Osteology of the Clupeoid Fishes_,
Proc. Zoo. Soc., Lond., 1904, vol. 11, p. 448.]

A half-tone can be put on to a line block during its manufacture. All that the draughtsman has to do, is to indicate by blue pencil lines those parts on which he requires the dots, which give the half-tone, to be placed, and to select the pattern of the stipple he desires to be used. The result may appear somewhat mechanical since the dots are regularly arranged, but a drawing sometimes may be considerably improved by this means if used with judgment. It is frequently employed in representing drapery, and many examples may be found on those pages of newspapers devoted to ladies' dress (Fig. 31; see also Fig. 32).

THE DRAWING OF DIAGRAMS AND APPARATUS. Much valuable information may be conveyed by diagrams; in fact, these could be used more freely than they are.

The principles to be borne in mind are the same as for other ink drawings. They should always be drawn upon an enlarged scale, and with as little detail as possible, which generally should be indicated in the most conventional ways--dots, black spaces, lines, and so on (Figures 33 and 34). The main thing to be aimed at is clearness, so that it is often necessary to sacrifice true relative proportions in order to gain this end (Fig. 34).

A Diagram from the _Annals of Botany_, 1912, Vol. 26.]

In certain cases it is possible to combine detail and diagram in one drawing; this is shewn in Fig. 32, taken from Dr. Ridewood's admirably illustrated memoir on the _Gills of Lamellibranchiata_ (Transactions of the Royal Society of London, B. vol. 195, 1903). The shading employed was either done by the draughtsman (at _ch_ and in the cells with irregularly arranged dots), or else was put on the block during its manufacture (_af_). If a lens be used, the difference will at once be obvious.

The finished drawing should be bold and neat, and all lettering should be very clear. If several figures are included in one diagram they may be separated one from the other by ruled lines, and in no case should one tier of figures--taking the frames as the boundaries--unevenly overlap another tier, otherwise the diagram, to use an expressive phrase, will look "like a pig with one ear."

Under the heading of diagrams must be included the representation of apparatus. There are two ways of drawing apparatus; the objects may be drawn as a study in still life, as, for example, in many of the figures illustrating Deschanel's _Natural Philosophy_ (London, 1890) or they may be represented in a purely conventional fashion. The latter is the better way, and it is preferable to draw for the most part in section in order that all connections, inlets, outlets, etc., may be clearly shewn.

A study of a good example is infinitely better than a written description, wherefore Figure 35 has been inserted.

It will be observed that all glass vessels and tubing are represented in section, and in the thermometers, the fine capillary bores are represented by a single line in each case; corks by diagonal shading; wood by lines in imitation of its grain; metal parts by vertical shading or dead black; more or less still liquids by a series of lines broken below and continuous at the surface, and gradually becoming closer and closer together towards the surface. Mercury, on the other hand, may be indicated by dead black relieved by a few white lines to represent its reflecting surface, also its free surface may be drawn convex. Finally thumb screws may be shewn by a combination of black areas and vertical shading.

These conventionalities need not all be followed; for instance, rubber connexions may be indicated by broad black lines and wood by diagonal shading.

The drawing should be very bold and the different parts clearly and freely indicated by writing or "printing."

THE DRAWING OF MAPS. In the drawing of maps for reproduction by the line block process, if an existing map serves the purpose, a tracing may be made in ink on translucent linen. If, on the other hand, the author has to make his own map, the problem becomes more difficult.

For the obtaining of the data for map making information must be sought for elsewhere, since we are only concerned in the preparation of the map for publication. And as regards this, but few general rules can be laid down since the character of maps is so diverse.

The amount of detail in the physical features represented depends to a great extent upon the scale. Thus streams of a greater breadth than, say, 10 feet, may in large scale maps be represented by double lines, whilst no stream less than 2 feet in breadth will be shewn in low scale maps.

_a_ Contoured.

_b_ Spot-levels.

_c_ Layered.

These three figures illustrate in three different ways the varying levels of a piece of ground surveyed by Prof. F. W. Oliver and Mr. A. G. Tansley.]