Page:EB1911 - Volume 22.djvu/423

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409
PROCESS


the attempts that were being made to reproduce his work mechanically without the intervention of the translator or interpreter. The ideal of an artist would naturally be a reproduction of his work in facsimile, which retained all, or as many as possible of, the individual characteristics of his work; and to give him this was the aim of the school of wood engravers which originated in the United States and made a last stand to maintain the position of their art in the field of book illustration. By a system of extremely fine work the American wood engravers were able to keep much closer to the tones of an originafthan had previously been possible; but the result was obtained at the sacrifice of the artistic rendering of the best old engravings, and was so mechanical in its character that when it had to compete with a real mechanical process the engraving could not hold its ground, the enormous difference in the cost of production being a factor of sufficient importance in itself to make it impossible for the engraving to retain the field. Asimilar development had been going on in the other branches of engraving. The line engraver and the etcher, to whom had been entrusted the interpreting of works of art first produced in other forms, found themselves faced by mechanical reproductions in plate form which, while preserving more of the character of the original work, were produced in much less time and at a greatly reduced cost. It has thus come about that the last quarter of the 19th century witnessed the dispossession of the hand engraver from the field of interpretative engraving, and the occupation of his position by the chemist and the mechanician. The term “ process, ” which has come to be applied to all photo-mechanical reproductions, is a somewhat unfortunate one, inasmuch as it is descriptive of nothing. From time to time various names have been given to its varying forms, indicative either of the name of the inventor or of some peculiarity of method. Zincography, gillotype, photogravure, heliogravure, heliotype, photo type, albertype, are illustrations of the kind of name given often to very slightly varying applications of the same principle, but usage has come to apply the term “ process ” to any printing surface that is produced by chemical and mechanical means. The whole 'of these processes may be arranged under three heads: (1) relief; (2) intaglio; (3) planographic. r. Relief Processes.-An engraving in relief is one in which the printing surface stands up above the surrounding ground. The history of the development of relief processes is really the history of photography (q.'v.); for whilst attempts were made to obtain results without the aid of photography, by drawing upon plates with prepared chalk or ink, “ rolling them up ” with printer's ink and etching away the ground with acid, as in the case of zincography, the real progress of all process has been upon the lines of photography; and to Niepce and Daguerre may be attributed the origin of the modern mechanical and chemical processes.

Speaking broadly, all the modern “processes ” are the outcome of a discovery by Mungo Ponton that a preparation of albumen or other colloid substance and bichromate of potash could be hardened and rendered insoluble and nonabsorbent in water by exposure to light, and that as a photographic negative permitted the passage through it of light in varying degrees of intensity, so a film of the preparation placed under a negative was liable to be hardened and rendered insoluble in degrees varying with the intensity of the light affecting it. This discovery governs the production of process blocks or plates of all kinds.

The methods of reproduction of pure line work differ greatly from those for the reproduction of originals in tone. As the Un first necessity in securing a good result is the suit¢

B, wks ability of the original to be reproduced, it is desirable to make clear the character of a good original. This should be of one tone or degree of colour all through. It may be all grey; it is better that it be all black. It may not be black in parts only and grey in others. The lines of an original may be of any variety of thickness. It is necessary, therefore, for the draughtsman to see that he works with a good black l

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ink, or ink that will tell as black when it is exposed to the photographic plate. Inks of a. Warm tone-that is, inclining to red or orange-yield better results than cold inks which incline to blue.

Most prepared liquid inks have a tendency to lose their blackness by exposure to the atmosphere on the removal of the cork from the bottle. The ideal ink is one freshly ground from a dry cake of colour when beginning work. Indian ink is goocljf well ground and kept sufficiently thick to assure the necessary blackness. It has the advantage of not washing up when colour in washes is passed over it, but it must be used freshly ground. The addition of a little Indian yellow, burnt sienna or sepia, gives a warmth of tone to it and renders it photographically more active. Bourgeois ink, prepared by Bourgeois of Paris, appears to be prepared with the admixture of some warm colour with the black base. It is a good ink for the purpose, and is prepared both in solid and liquid form. Lampblack gives good black lines; so does ivory black, which is warmer in tone than lampblack. Higgins' Indian ink or American drawing ink is an American ink made in liquid form which has the reputation of not fading by exposure. Stephens's Ebony Stain is a fine black medium which does not clog the pen; if it thickens and dries, it cracks off and does not corrode the pen. Besides the pen a brush brought to a fine point is much preferred by some artists, as it yields a line less monotonous than that given by a pen, though the brush cannot be used so freely. The paper used should be smooth and as white as possible. A paper is made with a surface coating of white chalk, which admits of the use of alscraper to remove lines or to break them up.

It is not possible to lay down a rule for the amount of reduction to be made when photographing for the reproduction; the liner the drawing the less should be the reduction made; but experience is the only guide. Sometimes, where the lines are very fine and the drawing minute in character, an enlargement is desirable. Where drawings are reduced too much, there is a tendency for the spaces between the lines to fill up, and to give a coarse, heavy result. Faulty drawing is not lessened by reduction. On the contrary, the fault becomes more evident, so it is desirable to make all necessary corrections in the drawing. The original drawing which has to be reproduced is photographed to the size of the required block. The negative taken is absolutely dense except where the lines of the drawing have affected it, and these are absolutely clear, admitting the unrestricted passage of light through them. A piece of planished copper or zinc is prepared or made sensitive to light by a preparation of albumen or gelatin and bichromate of potash spread upon its surface. The negative is laid upon the sensitized metal and placed in the light in the way an ordinary photograph is printed. The light passes through. the transparent lines of the negative and hardens the bi chroma ted film beneath them. Both negative and plate are then taken into a darkened room, , where the metal plate is rolled with an inked roller, placed in a bath of cold water and allowed to soak until the albumen and bichromate becomes so softened everywhere, except where the light has hardened them, that they all wash away, and nothing is left but the hardened lines. .The lines are dusted with asphalt, which by heat is melted on to them, and makes a ground which resists the action of acid. A coat of varnish is put over the back and edges of the plate, to protect them from the acid also, and only the spaces between the lines on the surface are left free to its action. The plate is then placed in a bath of dilute nitric acid, which eats away the metal where ever it is exposed; but it leaves the lines of the drawing, which are protected by the hardened film standing up above the eaten or etched surface; and these lines, which correspond to those of a wood engraving, are the printing surface of the plate. The plate is mounted on a wood or metal block, made type-high, and it can then be used along with type in the printing-press. Various devices have been resorted to that effects of tone may be obtained by means of the simple line process. Grained pers with a surface of chalk, upon which are printed close-rulerigmes crossing at right angles, or rows of dots ve the papers a hea, fiat, “ tone, " upon which a drawing can lie made in pencil, chlalyk or ink, and gradations of tone introduced by means of scrapers, which remove partially or entirely the black ruled lines or dots, leaving, if desired, high lights of pure white. A drawing on such