SCIENCE IN THE INDUSTRIAL WORLD 



difficult to use and is not practical, but by making use 

 of photography the same effect may be produced if the 

 drawing is made in the ordinary method with pen on 

 white paper. For the negative made by the camera 

 reverses the lights as they appear in nature, the black 

 lines on the white paper appearing on the photographic 

 negative as transparent lines on a black background- 

 like the scratches on the smoked glass, just referred to. 



Such a negative is then placed over a sensitized zinc 

 plate and printed in the same manner as the photo- 

 graphic plate. The light passing through the open- 

 ings in the glass plate corresponding to the lines of the 

 drawing hardens the bichromate mixture beneath. 

 The zinc plate is then "rolled up" with an ink-roller 

 carrying an acid-resisting ink, placed in water, and de- 

 veloped. Wherever the light has penetrated the hard- 

 ened bichromate mixture remains, the other portions 

 being washed away. The plate is then dried and 

 strengthened by a resinous powder, and after being 

 slightly heated is placed in the acid bath. 



In this manner a drawing may be reproduced with 

 the greatest fidelity, every pen stroke of the artist ap- 

 pearing exactly as it was made in the original. Here 

 was a process that was at once rapid, cheap, and 

 absolutely accurate, and this is the method in use to- 

 day for reproducing pen drawings as used in news- 

 papers and other publications. 



This discovery was the first great blow to the wood- 

 engraver, who could no longer hope to compete with so 

 simple and rapid a process which, in the end, interpreted 

 the work of the artist fully as well, if not better, than 



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