86 



SCIENCE-GOSSIP. 



[April 1, 1866. 



PHOTOGRAPHIC GOSSIP. 



OEVERAL valuable novelties are now on the eve 

 **s of coming into practical use by which photo- 

 graphy may attain popularity as a book-illustrating 

 medium. Hitherto the processes have all been more 

 or less imperfect, because they were too complicated, 

 troublesome, or incapable of rendering the grada- 

 tions of tone, or were only adapted for reproducing 

 works executed in lines, or because, requiring con- 

 siderable assistance from the engraver, they were 

 too costly. Mr. Woodbury's new " Photo-Relief 

 Printing Process" is exceedingly simple, renders the 

 delicate gradations of a "negative" from nature, 

 and requires no aid from either artist or engraver. 



You will readily perceive that white paper, visible 

 through layers of semi-opaque material, appears 

 lighter or darker according to the thicknesses 

 of these layers. Thus, for instance, a mixture of 

 gelatine and lamp-black, placed on a white surface, 

 so that it increased gradually in thickness, would 

 range from the white of the paper through deepen- 

 ing gradations of gray into black. On this simple 

 principle the " Photo-Relief " process is based. 



To a sheet of glass a piece of polished talc is 

 made to adhere with moisture. Eour ounces of 

 Nelson's opaque gelatine, dissolved in twenty ounces 

 of water, clarified with white of egg, and filtered 

 through muslin, is mixed with sixty grains of bi- 

 chromate of ammonia, dissolved in half an ounce 

 of warm water, to which a bluish tint has been 

 given with a little transparent pigment. The 

 mounted talc is coated with a smooth uniform film 

 of the above mixture, and, when set, it is removed 

 from the glass, and placed, face downward, on a 

 piece of blotting-paper, to enable the operator to 

 carefully clean the uncoated side. The talc is then 

 laid upon a negative in the usual way; on it is 

 placed another sheet of glass, and the three are 

 fastened together with elastic bands. It is next ex- 

 posed to light falling upon it through a condenser 

 until the requisite effect is produced on the film, 

 when it is taken from between the two glasses and 

 placed in hot water. Where the negative was most 

 opaque, and the light consequently acted least, the 

 bichvomated gelatine dissolves away. Where the 

 negative was most transparent, and the light, conse- 

 quently, acted most, the gelatine is unaffected by 

 the hot water; and so, in the same degrees in which 

 the light acted, parts of the gelatine surface are 

 more or less dissolved, and parts remain more or 

 less unaffected. You at once see that when taken 

 from the hot water there must be upon the talc an 

 impression from the negative in which what should 

 be the darkest parts are represented by being 

 highest in relief, and what should be the lightest 

 parts by not being in relief at all. To get an intaglio 

 from this, a sheet of soft metal (a mixture of type 



metal with lead) is placed over the talc, the two are 

 put between two perfectly true planes of steel, and 

 hydraulic pressure is applied at the rate of about 

 four tons to each square inch of surface. In less 

 than a minute we get the required intaglio, sharp, 

 clean, and perfect ; while the gelatine relief is un- 

 injured, and may be frequently used again. 



The intaglio is now placed in our printing-press, 

 which, in appearance, is a little shallow box with a 

 hinged lid. In the lid of this box there is a sheet 

 of plate-glass, and at the bottom of it there is 

 another, which can be raised or lowered by screws 

 working through the bottom of the box. On the 

 lower glass we place our metal impression, close the 

 lid, and turn the screws until every part of the 

 intaglio is in close contact with the upper glass in 

 the lid, which is straightway opened and turned 

 back. We now take our " ink," which is the afore- 

 said gelatine and lamp-black, or any other suitable 

 pigment, fill up the intaglio to one level surface with 

 it, place our paper on it, shut down the lid, wait about 

 half a minute, open the box, and take out what ap- 

 pears to be an ordinary photograph, the only apparent 

 difference being a slight effect of relief in the darkest 

 parts, which decreases and almost disappears as the 

 image dries. To render prints so obtained perma- 

 nent, they may be immersed in a solution of alum, 

 and afterwards rinsed in water. 



A method of printing photographs precisely 

 similar to the above in its main features, but in 

 which the intaglio is obtained by the electrotype 

 process while the print in relief is wet, has been 

 published by Mr. Swan, of Newcastle, and we have 

 seen very beautiful photographs produced by this 

 gentleman's invention. 



In each of the above cases the prints are obtained 

 separately, and to use type with them is clearly out 

 of the question ; but another new process of hardly 

 less value is now being introduced by Mr. Hancock, 

 of Lewisham, by which photography produces 

 electrotypes to be used as ordinary wood engravings 

 are used. The specimens we have examined of this 

 process, printed with type by Mr. Watson, of 

 Hatton Garden, are extremely beautiful. Although 

 it is only applied to the reproduction of drawings or 

 engravings in lines, Mr. Hancock's process has all 

 the value claimed for the glyphographic, graphotype, 

 and other similar substitutes for wood-engraving, 

 combined with much greater simplicity, certainty, 

 and ease of working. We can easily conceive how an 

 artist's drawing or a line engraving may be photo- 

 graphed, and from the negative a print obtained 

 with degrees of relief by the use of bichromated 

 gelatine as in the process used by Mr. Woodbury. 

 After this it is not less easy to understand how an 

 electrotype may be obtained in the way Mr. Swan 

 adopts, and so we get at a process which, if not 

 Mr. Hancock's, would at least serve the same 

 purposes. J. W. W. 



