1878.] to the Beproduction of Maps and Plans. Ill 



The plates obtained by this method show very good half-tone with an 

 almost imperceptible grain, giving the effect of a fine chalk-drawing. 



I have lately tried to obtain the images upon the copper by the double 

 transfer process, making use of a flexible temporary support, consisting 

 of paper coated with india-rubber, as first proposed by Swan, which can 

 easily be removed with benzole after the transfer of the gelatine image to 

 the copper. The ' grain' is given to the image by soaking it in water after 

 the removal of the india-rubber paper, and then applying the solution of 

 tannin in alcohol. This plan seems likely to be successful, if so, it will 

 greatly simplify the operations and enable engraved plates to be obtained 

 from any ordinary negative without the trouble of reversing. 



By electrotyj^ing direct from the gelatine relief, the results are always 

 rather heavier and coarser than they should be, because, although hardened 

 and insoluble, the gelatine relief can always absorb a little of the copper 

 solution in the depositing trough and consequently the image swells and 

 loses sharpness. 



The strong tanning given to the gelatine film and the preliminary 

 coating of wax before metallising the surface obviate this defect to a consid- 

 erable extent ; but it may perhaps be better to obtain a matrix in lead by 

 pressure from the gelatine relief, and then to obtain the printing plate by 

 electrotyping twice from the lead matrix. This is a more round-about and 

 expensive method, but is likely to yield finer results and has been adopted 

 by Woodbury and Eousselon in the processes next to be considered. 



The process is simple and if it could be successfully worked out it 

 might be usefully employed in this country in reproducing shaded maps 

 and for other miscellaneous purposes. It has the very great advantage 

 over photo-collotype that the plates can be corrected, if necessary, and can 

 be printed in any numbers in the ordinary copper-plate press without risk 

 of breakage or damage to the printing surface. 



Woodhury-type onetJiods. — It has already been shown that in the Wood- 

 bury-type process the photographic image is impressed into a soft metal 

 plate by means of a relief in insoluble gelatine on a collodion support, and 

 that instead of impressions being printed in ordinary printers' ink they are 

 made in coloured gelatine. In such prints the gradation of shade is conti- 

 nuous and there is no perceptible grain. 



Mr. Woodbury has proposed an ingenious method for obtaining gela- 

 tine reliefs with a granular surface, so that, when impressed into soft metal, 

 electrotypes in copper may be obtained from the latter, which will serve as 

 printing-plates for printing with printers' ink in the copper-plate press, and 

 yield superior results to those obtained by electrotyping immediately from 

 the gelatine relief. 



A plate of glass is waxed and coated with a thin film of collodion, and a 



