July 1, 1886.] 



KNOWLEDGE ♦ 



177 



printing-press was briefly as follows. The artist drew his 

 design on the boxwood block — the engraver cut that design 

 — and the block afforded a certain limited amount of im- 

 pressions before it was worn out and useless. Then the 

 electrotype process came in. The soft block was no longer 

 used in the press, but an impression in wax was taken of 

 its engraved surface, and this waxen mould was subsequently 

 used in the electric bath to furnish a shell of copper, or 

 electrotype, which, when afterwards strengthened and 

 mounted, would furnish a large number of impressions. 

 Tlie wood block itself was put away as an original from 

 which other wax imj)ressions and electrotypes could be 

 taken without limit. But let it be borne in mind that, 

 with the cutting of the block, the work of the artist — 

 regarded as a drawing which would otherwise be valuable — 

 was altogether destroyed. 



Improvements in photography changed all this. The 

 artist now executes his work on fine cardboard, with pencil 

 and brush. The picture is in black and white, but not 

 necessarily in lines, as in the old days of drawing on wood 

 blocks. It is drawn in tints — that is to say, the various 

 lights and shades are expressed by washes of colour made up 

 with Indian ink and Chinese white — many of these com- 

 ])ositions having a great likeness to the old-fashioned sepia 

 drawings, but possessing a colder colour. The next stage 

 in the process is to copy the drawing on to a wood block. 

 It is here that the camera comes upon the scene, with an 

 advantage not possessed by any other form of copying. The 

 original can be reduced or enlarged to any size required. 

 In practice, enlarging is never, or seldom, asked for ; but 

 the reduction of a large drawing to a small block is a frequent 

 operation. This having been done, the block, bearing a most 

 faithful representation of the original, is handed to the 

 engraver, who rapidly translates its varying shades into 

 sharply-cut lines, which accurately convey to the eye, by 

 their varying proximity to one another, the force and mean- 

 ing of the original work. And here we come to one of the 

 most important features of the operation. The original 

 remains intact and unaltered in every way, and has a 

 market value depending upon the status of the artist who 

 drew it. We recently saw a large collection of these black- 

 and-white pictures, as they are commonly called. They 

 had all been used for reproduction, and had done duty in 

 various publications. They were now for sale, ami the 

 ])rices realised varied from twenty pounds down to as many 

 shillings. 



But this is not the only change that photography has 

 brought to the engraver's art. In great measure it has 

 superseded that art. So much so, indeed, has this result 

 been brought about that many engravers who formerly had 

 no difficulty in finding constant work have now so little to 

 do that they have seriously to think of beginning the world 

 afresh. This is the sad side of every improvement which 

 increased knowledge renders possible. The individual 

 suff'ers for the general good. A lai-ge jiroportion of 

 the ])ictures which appear in our periodicals — including 

 those of the highest class— have been drawn, photogiviphed, 

 and made ready for the printing-press without any aid 

 vv'hatever from the hand of the engraver. It seems at 

 fir.st sight little short of marvellous that Ihe delicate 

 and fragile image formed by the sun on a glass plate — 

 an image so fragile that it is often torn by the accidental 

 touch of the finger-nail— can by mere mechanical means 

 be changed into a metal plate so rigid and strong that 

 copies by tens of thousands cau be obtained from it in the 

 printing-press. That this is strictly within the truth our 

 readers have lately had evidence in those star photographs 

 which have recently appeared in these pages, and which 

 were produced, as has been already stated, quite inde- 



pendently of the engraver's art. The daily newspapers 

 oocasionally reproduce pictures of a rough kind, which are 

 also traceable to automatic processes ; and here wo have 

 indications that the issue of a daily illustrated journal 

 may become probable — it is certaiidy possible — in the 

 near future. 



The process by which a mere line picture (we mean one 

 in which absolute black and absolute white are the only 

 effects involved — a picture, that is to say, without greys or 

 half-tones) can be repi'oduced is astonishingly simple. The 

 operations depend upon the curious property possessed by a 

 certain class of chemical salts — the dichromates of the 

 alkalies — in rendering gelatine or any colloid substance 

 insoluble after insolation, or exposure to light. Taking the 

 common red salt, potassic dichromate, as a type of those 

 mentioned, let us see how it enables the operator to change 

 a line drawing into a block ready for the printing-press. 



First of all, a warm solution of gelatine and water is 

 charged with a certain quantit}' of the dichromate, or 

 bichromate of potash as it is familiarly called. This mixture 

 is brushed over a sheet of paper, which paper is then hung 

 up in a dark room to dry. In the meantime a negative 

 image on glass has been tiken of the line drawing by means 

 of the camera — an image in which the lights and .shades are 

 all reversed, and in which, therefore, the original black 

 lines of the drawing are represented by lines of clear glass 

 on a black ground. The negative is placed in a printing- 

 frame, and is backed up with the prepared paper. It is 

 now exposed to light for some minutes, during which time 

 only those portions of the paper can be affected by such 

 exposure as are comprised in the lines of the drawing — ■ 

 for those portions only of the glass negative will permit 

 the light to go through it. When the right amount 

 of exposure has been given, the negative and the 

 paper are again taken into darkness, or dai-kness only 

 relieved by red illumination, which has no effect on the 

 sensitive chemical employed. The paper, even by this dim 

 light, is seen to have a fxint image upon it, but this is for 

 the moment disregarded. It now receives a uniform coating 

 of greasy ink, until every trace of its former appearance is 

 obliterated. The paper is next transferred to a bath of 

 hot water ; and now a very curious thing happens. The 

 bichromated gelatine has been rendered quite in.soluble by 

 the action of the light in certain parts, and thoss jjarts com- 

 prise the lines of the drawing. The rest of the surface is 

 still soluble in the hot water, and immediately begins to dis- 

 solve. In a very few minutes this stage of the work is 

 complete, and the original drawing stands revealed in in- 

 soluble lines covered with greasy ink. A zinc plate is now 

 required, to the siirlace of which that greasy image can be 

 transferred. The zinc is then placed in an acid bath, so that 

 the metal, where not protected by the ink, is eaten away — 

 and lo ! the drawing is left in relief This zinoographio 

 plate can now bj mounted on a wooden block for direct use 

 in the printing- jtress, or it can be employed for affording 

 wax moulds from which any number of electros cau be 

 obtained. It need hardly be said that the cost of producing 

 such a block is a fraction of the cost of otre cut by hand. 



We see, then, that a pr-inting surface which can be used 

 in the ordinary printing-press is ol)tairiable by the action of 

 light, coupled with certain chemical and mechanical opora- 

 tions, but dispensing from first to last with the work of the 

 engraver. But the picture must be expressed in either lines 

 or dots, or a combination of both, so that innumerable points 

 are produced to which the printing-ink can attach itself. 

 Many attempts have been made to soften the effect of those 

 markings, so as to get some .appearance of half-tone. The best 

 method, perhaps, is that which employs a special form of 

 paper for the original drawing. Specimens of such prepared 



