November 1, 1897.] 



KNOWLEDGE 



253 



representing creation, preservation, and destruction ; and 

 expressions like the "three Fates," the "three Muses," the 

 "three Furies," and the "three Graces" are all found in the 

 Hindu vocabulary. The primitive Aryans accorded a kind of 

 pre-eminence to triads of natural objects, such as the sky, 

 atmosphere, and sun ; and give many proofs of their pre- 

 ference to group the objects of their adoration in triple 

 combinations, to which a sacred significance not unmixed 

 with superstition was attached by the primitive races of 

 the East. The Mohammedans have also shown that they 

 do not look with disfavour upon the triple arrangement of 

 everything material. All these instances and many others 

 brought together by Mr. Laharry, when considered with 

 the Trinity of the Christian faith, show that the mystic 

 number three has had a very distinct influence upon the 

 thoughts of the nations of the world. 



PHOTOGRAPHY IN ILLUSTRATION. 



By H. Snowden Wabd, F.R.F.H., Editor of "The riiotoi/ram." 



SO steady and so evenly progressive has been the 

 growth of photographic illustration in the past few 

 years, that few realize what an important — what a 

 revolutionary — power photography has been. If I 

 had but time to sketch the mere romance of the 

 subject it would make a fascinating Christmas magazine 

 article even for the " general reader." For the relentless 

 march of progress has meant suffering, stern hardship, 

 and even death to some of those craftsmen whose crafts 

 have been supplanted ; and even the votaries of the photo 

 processes themselves — the men who have worked out the 

 processes by which we are enabled to lavishly illustrate 

 our penny papers — have had amongst their ranks as real 

 martyrs as ever suffered for religious zeal. Death from 

 practical starvation, penniless widows and orphans, loss of 

 reason and confinement in the madhouse — all these have 

 been amongst the rewards given by a grateful world to the 

 men who have laboured to increase man's knowledge and 

 man's power, even in the unromantio realm of photographic 

 illustration. 



Perhaps this is a little beside my proper subject, but all 

 along the line of the history are constant glimpses off 

 romance. In the broad lines we may point to photoL 

 mechanical processes as having, first, killed the old school 

 of wood engraving. Such " woodpeckers " as still remain 

 with us mostly earn a curtailed and often precarious 

 Income by engraving mechanical and engineering subjects, 

 catalogue illustrations for rough printing, poster blocks, 

 and other inartistic work. Much the same fate, though 

 even more completely, has befallen the steel-plate and 

 copper-plate engravers, whose work in the reproduction of 

 pictures cannot be lost without regret. Even the illus- 

 trators, the black-and-white artists, have found their con- 

 ditions greatly changed by " process," for since the half- 

 tone can make passable reproductions of poor photographic 

 originals, many of the draughtsmen find their work no 

 longer in demand, while others have been forced to com- 

 pletely alter their methods. 



In the great industry of paper making, too, " process " 

 has worked nothing less than a revolution, based on the 

 demand of half-tone printers for highly finished and clay- 

 faced papers — of which I will say more anon. 



Most photo-mechanical processes are based on the fact 

 that certain colloid substances, gelatines, gums, etc., when 

 treated with a bichromate salt, become sensitive to light in 

 a peculiar way. Of course, everyone knows that certain 

 silver salts, when suspended in gelatine or albumen and 



laid upon paper, have such a sensitiveness to light that 

 upon exposure to it they change from a practically white 

 colour to a chocolate-brown or black. This is the basis 

 of the ordinary photographic printing process. The 

 bichromated surfaces, on the other hand, though their 

 colour changes but little, go through considerable changes 

 in other ways. For instance, a bichromated gelatine is 

 soluble in water before exposure to light, but the light's 

 action renders it insoluble ; and on this fact are based 

 almost the whole of the photo-mechanical processes. 

 Another action upon bichromated surfaces is that what 

 will remain soft and " tacky " in the dark, will become 

 hard and horn-like under exposure to light. As these 

 changes take place in proportion to the amount of light 

 falling upon the sensitive surface, it is obvious that by 

 using a photographic negative as a shield, parts of the 

 surface (under the densest parts of the negative) may be 

 left perfectly soluble ; parts (under the semi-transparent 

 parts of the negative) will be less soluble ; and parts (where 

 the transparent portion of the negative allows the light to 

 act fully) will be perfectly insoluble. This is the basis of 

 photo-mechanical work. 



The processes may be divided into three chief classes : — 



A, relief printing, as in half-tone and line zincography ; 



B, surface printing, as in collotype and photo-lithography ; 

 and C, intaglio printing, as in photo-aquatint, photogravure, 

 and Woodburytype. Of the applications of the work to 

 decorative purposes — to pottery decoration, to the etching 

 and damascening of metals, to the printing of tiles, to the 

 production of plaster and other reliefs and transparencies — 

 I must say nothing in detail, though this branch of the 

 subject is extremely fascinating. 



The relief-printing processes of half-tone and line 

 zincography are by far the most generally used, because 

 by their means are produced printing blocks which may be 

 printed in the letterpress printing machine, in the same 

 forme with ordinary type. The other processes, which 

 cannot be printed on the letterpress machine, are only 

 suitable for separate illustrations, supplements, frontis- 

 pieces, etc. In letterpress printing the printing surface of 

 the type and blocks consists of lines and dots of metal, all 

 on one level, while the whites are represented by depressions 

 in the metal. The ink is applied to the raised surface, and 

 does not enter the depressions, so that when the paper is 

 pressed against the forme the ink from the raised surface 

 makes the print. In this method all parts are equally 

 inked, so that any effect of half-tone or gradation in a 

 picture must be obtained by varying the size of the lines 

 and dots in relation to the spaces between them. In line 

 zincography this variation is made by the artist, who 

 produces a drawing in strong black ink on white paper, 

 usually making the drawing about a third larger than the 

 printed picture is intended to be, because the fineness and 

 crispness of the lines is increased by camera reduction. 



In line zincography this original drawing is placed upon 

 an easel, usually illuminated by electric light. A camera 

 is placed before it, and the image focussed and arranged 

 so as to fall upon the sensitive plate in the size intended 

 for the finished block. After exposure, the plate is 

 developed, and a negative is obtained in which the white 

 spaces of the picture are represented by a dense opaque 

 deposit of silver, while the lines are transparent and clear. 



This negative is then forced into contact with a sheet of 

 metal (usually zinc), the face of which is coated with a 

 sensitive film, somewhat similar to those indicated in an 

 earlier paragraph. The light passing to this film through 

 the transparent lines of the negative, produces, under them, 

 insoluble lines of film. When the exposure to light has 

 lasted long enough, the coated metal plate is taken from the 



