SCIENCE IN THE INDUSTRIAL WORLD 



printed first, or the order in which the other two are 

 superimposed upon it; the result should be the same 

 in any case, as the total amount of pigment covering 

 any point in the picture will be the same. In actual 

 practice, however, owing to mechanical difficulties, and 

 for other reasons, this order of imposing the blocks is of 

 great importance, the best results being obtained by 

 certain definite order in printing certain pictures which 

 would be less satisfactorily reproduced if this order were 

 reversed. 



It is obvious that one of the great difficulties in such 

 a process is that of determining the exact shade of 

 yellow, red, and blue pigment to be used hi the print- 

 ing, but this is usually done by practical experiment. 

 Another difficulty is the matter of accurately registering 

 each block so that it prints hi exactly the same position 

 as the other two. But these difficulties have been 

 practically overcome so that at present three-color pic- 

 tures of mediocre quality can be made with relative 

 cheapness and expedition; while fine pictures faithful 

 in color and extremely artistic in effect may be produced 

 at a relatively low price. 



Most good three-color engravers have their own 

 special methods of making filters, and preparing and 

 printing the cuts. In skilful hands a great latitude is 

 allowable in the selection of colors for the different 

 filters, inks, etc., and many engravers prepare their 

 own filters and inks. One prominent firm, for example, 

 uses green, violet, and red filters, and produces beauti- 

 ful effects by this combination. 



A great difficulty is always found in producing clear, 

 [214] 



