PHOTOGRAPHY, SCIENTIFIC ASPECTS 



changing, would be something like an hour and 

 three quarters. But this time is not constant, and 

 as a rule test-negatives are made and developed 

 with various filters before the final negatives are 

 taken. 



It is obvious that when the negative is exposed to light 

 coming through each of these filters, impressions will 

 only be made and necessary deposits formed in develop- 

 ment, at such points indicated by the position of certain 

 colors. When such negatives are developed, only such 

 positions of the object appear as are represented by the 

 color in question. If positives are made from such 

 negatives, and these stained red, green, and blue, re- 

 spectively, according to the filter used, a transparency of 

 the object photographed may be made, reproducing the 

 natural colors with great fidelity. 



Sanger-Shepherd and others have perfected a process 

 whereby prints may be made from these positives by the 

 use of colored inks. The gelatine representing the 

 primary color on each plate is slightly raised, and will 

 absorb the ink as required. By carefully registering 

 each of these impressions beautiful colored photographs 

 may be made. To reproduce and print such colored 

 photographs, however, is quite beyond the range of the 

 ordinary amateur photographer. 



Generally speaking, all indirect color photography 

 is based upon some such artificial and arbitrary sep- 

 aration of color, and the achieved results have been 

 obtained by working in two different ways; first, by 

 the production of three images, one for each of the 

 required colors, and, second, by the production of a 



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