194 COLOR PHOTOGRAPHY. 



The color reproduction by the substances used by Seebeck and Poi- 

 teviu and the degree of its accuracy are therefore explained by the fact 

 that they possess the characteristics of a color-sensitive substance as 

 approximately as is required by the degree of accuracy of the color 

 reproduction. 



XIV. — The Standing- of Color Photography with Body Colors 

 with reference to the color printing and interference 

 Processes — Possibility of the Perfection of Color Pho- 

 tography. 



Color photography with the aid of color-receptive substances will be 

 here distinguished as body- color photography. 



It resembles the process recently worked out by H. W. Vogel ] of 

 color printing in so far that the colors in both cases are rej)roduced by 

 body colors. Both methods require also the presence of regularly 

 absorbing light-sensitive substances, which admit of the application of 

 the Yogel fundamental law of optical sensitizers. Progress in the dis- 

 covery of such substances will be advantageous for both processes. 



The methods employing body colors lend themselves the more 

 readily to reproduction of pictures, since the colors appear by trans- 

 mitted light. For this purpose it would be necessary to use transpar- 

 ent plates, such as have been of late employed by Yeress. 2 The color- 

 printing process naturally has the advantage over all others in the 

 capacity for reproductions. But the method employing body colors is 

 at least superior to the interference process in this respect. 



This method more resembles the interference process, however, in 

 that the colors are directly produced by the illumination. Since the 

 resulting colors are, moreover, not apparent, but real body colors this 

 process may perhaps be looked upon as promising the ideal of color 

 photography. Its results are, to be sure, at present far removed from 

 the ideal, but perhaps this will be otherwise after the recognition of 

 the foundation upon which the process rests. 



The Seebeck and Poitevin processes choose a roundabout way. 

 The properties of a color-receptive substance are very complicated. 

 But after it is shown that such a substance reproduces colors correctly 

 one can conversely base his considerations on the capacity for correct 

 color reproduction, and pursue the inquiry, What are the simplest char- 

 acteristics which are required for this purpose % 



I believe that these are to be found in a black mixture of three regu- 

 larly absorbing light-sensitive substances which decompose with the 

 formation of white products. To be sure, however, the greatest variety 

 in this process is conceivable. 



There are different ways which may be imagined in which fixing 



1 Verh. der pbys. Ges. z. Berlin. Ann. der Physik und Cliemie, 46, page 521, 1892. 



2 See Elder's Jalirbuch fur PUotograpkie, page 46, 1891. 



