SCIENCE IN THE INDUSTRIAL WORLD 



lar surface and more closely approach facsimile repro- 

 ductions than perhaps any other form. But the making 

 of such prints from photogravure plates is a slow task 

 requiring special printing and considerable skill, making 

 such reproduction too expensive for use as ordinary il- 

 lustrations. Furthermore, since each picture must be 

 printed separately, the photogravure process cannot be 

 used in connection with type. 



While the majority of photogravure processes are 

 based on the principle of the sunken printing-surface, 

 it is possible to reverse this, making the photogravure 

 plate as relief work. In this process the granular effect 

 is obtained by the use of the bitumen dust the same as 

 in the other, but the relief effect is obtained by certain 

 processes of depositing particles of metal rather than 

 by biting out surfaces with an acid. There is little choice 

 between the results of these two methods. 



Quite recently several secret processes of reproducing 

 pictures have been invented which represent a middle 

 ground between the relatively slow and expensive pho- 

 togravure process and the cheap and rapid half-tone. 

 The results obtained by these processes are somewhat 

 inferior to photogravure work, while the expense and 

 speed involved in their production compare favorably 

 with a better class of half-tone work. The exact method 

 of producing such illustrations is not generally known, 

 but it is understood that no new principles are involved, 

 and the secret lies mostly in the perfection of the print- 

 ing-machine rather than in any new departure from 

 well-known engraving-processes. 



In the foregoing description of the development of the 



