Plate 7.—Half Tone reproduction
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 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.
