PRACTICAL PHOTO-MICROGRAPHY. 145 



raphers ; in photo-micrography tone of slide is a very subor- 

 dinate consideration, if, indeed, a black tone is not preferable. 



Dry Collodion, which in virtue of its tone is perhaps the 

 most suitable of all processes for landscape and portrait slides, 

 gives purity of high lights little if at all inferior to wet collo- 

 dion, but for camera copying the slowness of Dry Collodion 

 is against it. 



Gelatine-chloride plates are most valuable for contact print- 

 ing, giving great clearness and varying tones at will, but for 

 camera copying their excessive slowness is very unfavorable. 



Grelatine bromide plates made for the purpose work rapidly 

 and may be made to yield clear lights and good tones ; but 

 while assuredly the gelatine bromide process is the most con- 

 venient, and while its results under suitable conditions are in- 

 ferior to none, still the greatest care and much practice are 

 required in order that the working of the process may be 

 mastered. Foggy slides by this process are unfortunately very 

 common. 



We have now put the merits of these processes fairly be- 

 fore our Reader. If he makes his negatives of a suitable size 

 for contact printing we recommend on the whole the gelatine- 

 chloride process, or dry collodion. (The latter process, how- 

 ever, we must not detail here for want of space.) But gelatine 

 bromide may answer to perfection. 



For camera copying we strongly recommend the wet collo- 

 dion process, but as we fear few of our Readers will care to 

 face its difficulties, or rather its inconveniences, we give as an 

 alternative the gelatine bromide process. 



The usual size of a Lantern Slide plate is 3J inches square, 

 as a rule a mask is placed over this leaving an area of image 

 of about 2f inches diameter. 



To print by contact, the negative is placed face upwards in 

 a printing frame, a Lantern Slide plate is placed face to face 

 with the negative, the frame closed and the exposure made to 

 the light in the usual position, i. e., negative next the light. 

 It is advisable that the extreme edges of the lantern plate 



O i 



be protected from the light by a mask or the rebates of the 

 printing frame. 



