196 YEAR-BOOK OF FACTS. 



the printing paper prepared with the bichromate of potash, gum, and 

 lamp-black, or any other pigment, called the Chromo-carbon process 

 of printing. 



The action of* light on a coating of this composition produces the peculiar 

 effect of rendering it insoluble in water, and consequently when a sheet of paper 

 coated with it is placed in the printing frame under the collodion negative, the 

 outline of the plan is rendered insoluble in water, and remains on the paper 

 when all the remainder of the composition is washed away, and tints we have a 

 " positive" plan in ink of any colour which may be required. 



In comparing the reduced plans obtained by this process with those obtained 

 by the use of paper prepared with the nitrate of silver, we obtain no advantage 

 whatever, but, on the contrary, the prints are less clear and sharp in their outline. 



But by a new mode of treatment oftbesechromo-oarbon prints which has been in- 

 troduced by Capt, A. deO. Bcott, B.E., who hascharge of this branch of the work; 

 and Lai i Rider, K.K., who is a good photographer, and also possesses 



a considerable knowledge of chemistry, we can produce very sharp, clear lines. 

 The ink of the print after being Soaked in a saturated solution of caustic potash 

 or soda becomes, so to speak, disintegrated, and is then in a state which enables 

 US at once to rab down the print, an. I transfer the outline to the waxed surface 

 of a copper-plate for the engraver. This promises to be of great importance to 

 us, as after obtaining the photographed reductions ofthe maps we have hitherto 

 been obliged to make tracings from them in ink, for the purpose of transferring 

 the plan to the copper, the expense and delay of which will now be saved, whilst 



we run no risk of any error being made by the draughtsman. 

 We have also tried a method which is still more valuable, and by which the 



reduced print is in a state to be at once transferred to stone or zinc, from which 

 any number of copies can be taken, as in ordinary Lithographic "■' zinOOgraphia 

 printing, or for transfer to the waxed surface of the oopper-plates. To effect 

 this, the paper after being washed over with the solution of the bichromate of 

 potash and gum, and dried, is placed in the printing frame under the collodion 

 negative, ana alter exposure to the light, the whole Surface is coated over with 



Lithographic ink, and a stream ofhof water then poured over it j and as the portion 

 which was exposed to the light ia Insoluble, whilst the composition in ail other 

 parts being soluble is easily washed oil', we obtain at once the outline ofthe map 

 in a state ready for being transferred either to stone, zinc, or the copper-plate, 



or we can take the photograph on the zinc at once. 



This new method of printing from a negative is extremely simple 

 and inexpensive), and promises to be of great use to us. Sheet 1*0, 

 of Northumberland, litis been transferred to the copper-plate from 

 impressions taken by this process, and from the perfect in. inner in 

 which we tire able to transfer the impressions to zinc, we can, if re- 

 quired, print any Dumber of faithful copies of the ancient records of 

 the kingdom, such as Doomsday Booh, the Pipe RoUs, &c, at a 

 comparatively speaking very trifling cost. I have called this new 

 method Photo-zincography, and anticipate that it will become very 

 rally d k Col, not only to Government, but to the public at large, 

 lor producing perfectly accurate copies of documents of any kind. 



A j" a manuscript of the time of Edwafd I., copied and 



printed :.t tie' Ordnance Survey Office, under the direction ol Colonel 

 air Henry James, by means of the photo-sincograpbid process, has 

 been presented by the Photographic New to its readers. 



ON TI1K SHI, Alt <\VH:\. UY \. rl \l DKT.* 



Tin: Solar Camera, invented by Woodward, is one of the most 

 important improvements introduced in tin- art of photography since 



• Read to the British Association at Oxford. 



