THE BOOK OF THE LANTERN. 113 



portions of ether and alcohol, and, after filtering, the re- 

 constructed emulsion is ready for coating the plates. They 

 can be developed by a weak alkaline developer with pyro, 

 or by the ferrous-oxalate method, which will be described 

 later on, Mr. W. Brooks, of Reigate, has made a study 

 of this process, and supplies the emulsion ready made. 

 Messrs, Mawson and Swan have also lately advertised it, 

 so that it is hardly worth while for the worker to make it 

 for himself, 



WOODBURYTYPE PROCESS. 



This method yields results which cannot be sur- 

 passed, but it may be looked upon more as a com- 

 mercial process than one suited to the amateur worker, 

 for it necessitates the use of expensive plant. I shall 

 therefore dismiss it with a somewhat brief description, 

 albeit my chapters on slide-making would hardly be com- 

 plete without it, In the first place a relief is obtained by 

 employing gelatine, containing one of the bichromates of 

 the alkalies bichromate of potash, for instance. This 

 relief is placed upon a sheet of lead, and after the two 

 have been fixed in a steel frame, they are submitted to 

 hydraulic pressure, with the curious result that the tender 

 gelatine film preserves its delicate outlines, but the leaden 

 plate gives way, and these markings are pressed into it. 

 This leaden plate then forms a mould of the future picture, 

 its deepest parts representing the shades of that picture, 

 and its higher parts the lights. This is placed in a special 

 press, and a pool of gelatinous ink (made by dissolving any 

 suitable pigment in a warm solution of gelatine and water) 



I 



