PHOTOGRAPHIC AND MECHANICAL 



PROCESSES IN THE REPRODUCTION 



OF ILLUSTRATIONS 



By ROBERT STEELE 



There are very few books or articles which would not be the 

 better for a certain amount of illustration, while on the other 

 hand there are very few authors who could not suggest illustra- 

 tions or produce them themselves. Unfortunately, the steps 

 that lie between the rough sketch, the photograph, or the 

 water-colour drawing as it lies in the author's portfolio, and 

 the finished illustration as it is to appear in the book, are a 

 mystery to him, and he has no means of deciding what kind 

 of illustrations he can get from the material he has by him. 

 It is with a view of helping such an one to decide this ques- 

 tion that the following survey of modern methods of production 

 has been written. 



All mechanical reproductions to-day are based upon photo- 

 graphy. The ordinary process of taking a photograph depends 

 on the use of a lens to form a clear image of the object to be 

 photographed on the surface of a film at the back of the 

 camera. This film contains a compound of silver, which is 

 altered by the action of light so as to become insoluble in a 

 liquid which we call the " developer." The tones of the picture 

 on the sensitive film are thus represented by the varying 

 thicknesses of altered silver, and after the plate has been 

 sufficiently immersed in the developer, all the unaltered silver 

 is dissolved out, and a reversed picture or negative is left on 

 the film, in which the lights of the real picture are black and 

 the shadows are light. 



Line Blocks 



When the illustration required is in pure line, as, for example, 

 a diagram or a drawing, the process of reproduction is compara- 

 tively simple. A negative is produced in the ordinary manner, 

 except that it is reversed in a well-known way by a mirror. A 



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