242 PBACTICAL PHOTO-MICBOGKAPHY 



The plate should be cleaned and polished as before and then 

 coated with what is known as enamel collodion. When the 

 collodion has set, the print, which has been soaked in water, is 

 placed in contact with the collodion surface and squeegeed as 

 before ; this produces a still more highly glazed surface. The 

 latter process is, however, rarely necessary, as most P.O. P., or 

 bromide papers made with a glazed surface, can be rendered 

 sufficiently glossy without collodion. 



Lantern-slides. For projection purposes a positive on glass 

 is required, and these are generally referred to as lantern-slides. 

 Their production is quite simple, and is essentially the same 

 as the bromide-printing process on paper. As with ordinary 

 negative-making, dry -plates may be used ; or the wet-collodion 

 process may be adopted. If the negative from which the slide 

 is to be made is of the required size, then that known as the 

 contact-printing method is suitable, when dry-plates are used ; 

 but where the negative is larger than the size of the lantern- 

 slide, the process known as reduction must be resorted to. 

 Lantern-slides are always made 8J inches square ; and, 

 allowing for a margin for binding and masking, it follows 

 that no negative in which the part to be used is more than 

 3 inches square, can be employed for contact purposes. 

 Most makers of plates suitable for negative-making also 

 manufacture those for lantern-slides. Some recently intro- 

 duced by Messrs. Wratten & Wainwright are amongst the 

 best of these ; the grain of the ones supplied by them is 

 extremely fine, and they are capable of development by 

 almost any process. 



The process consists of putting a lantern-plate in a printing- 

 frame in contact with the negative to be printed from, so that 

 they are film to film. This must be done in the dark-room 

 by orange or yellow light. The exposure may be made 

 by any artificial light-source, and its length will depend 

 on the negative, source of light, and the sensitiveness of the 

 plate in use. Makers generally give in each box of plates a 

 sufficiently complete set of instructions both as to exposure 

 and development. 



In photo-micrographic work the slides are usually required 

 to be bright, and as a rule are preferably black in colour. The 

 metol-hydrokinone developer, already described, gives this 



