178 



DRAWING BY THE AID OF PHOTOGRAPHY [Ch. VI 



ink or pencil, the negative is made the size of the desired finished 

 picture. On the other hand if the negative is to be used for projec- 

 tion, it should be of about the size of a lantern slide (§ 290). 



§ 288. Drawings upon blue prints. — This is especially available 

 for objects with definite outlines and clear details like the wing veins 

 of insects (Comstock) or apparatus, furniture, etc. 



A negative of the object is made of the desired size and a blue 

 print made. Then with waterproof India ink all the lines are gone 



Fig. 108. Camera Obscura for Drawing, and Lantern Slide Making. 



(From Optic Projection). 



over, and all the points indicated which are to be shown in the finished 

 cut. 



Bleach out the blue by soaking the print in a solution of 10% 

 neutral oxalate of potash. Wash in water and dry on gauze. Only 

 the ink lines will show in the finished print. This line drawing can 

 then be lettered in any desired way, and the engraver can make a 

 line cut for the printing press. 



Ordinarily it is best to make the picture two or three times the 

 size of the final engraving. Defects are minimized in the reduction. 

 Always have the object in view in finishing the drawing. 



§ 289. Drawings on the back of photographic prints. — Instead 

 of making a blue print, a photographic print can be made of the 

 negative of the object to be drawn in lines. Use double thick devel- 

 oping paper (Cyco, Velox, etc.). 



For this the best method is to make a small negative of about the 

 size of a lantern slide, using a rather long focus objective so that all 



