FHOTOGRAFIIIC PROCESSES. 70 



appeared from the back of the plate; it is then 

 washed in frequent changes of water for several 

 hours, and finally put aside to drain. 



When dry, the plate is warmed before a clear fire, 

 the temperature not being raised higher than thy 

 hand can very comfortably bear, the varnish is then 

 applied in exactly the same manner as collodion, 

 and when all superfluous fluid has drained away, heat 

 is again applied ; the temperature being carried 

 much higher than at first, to prevent the formation 

 of a mat surface. Should the intensifier not be 

 used and the plate found to lack density after fixing, 

 the mercurial solution mentioned in the following 

 process may be applied, (as little exposure to actinic 

 light as possible being given before its application). 



When the reproduction of very minute markings 

 is necessary, dry plates never give as good re- 

 sults as the wet, at least in our hands ; they are, 

 however, sufficiently perfect for all practical pur- 

 poses, while the shortness of the exposure, cleanli- 

 ness of manipulation, and when purchased, the time 

 saved by the absence of any previous preparation, 

 almost counterbalance this disadvantage. 



Great care is required in using these plates, as the 

 slightest glimpse of actinic light will utterly spoil 

 them. A double thickness of ruby glass must be 

 substituted for the ordinary yellow glass of the 

 dark room, and even of this light, as little as possi- 

 ble should be allowed to reach them. The dark 

 slide should be carefully examined, and if of the 



