12 J. H. SMITH, Bleach-out Process of Colour Photography. 



to keep the balance of the colours, to employ colour 

 screens in front of the printing frame. These may require 

 to be changed according to the nature of the light which 

 is employed. In sunlight the prints print redder in tone 

 and in diffused light bluer. The blue tone is obviated by 

 a light orange filter, and the red tone by a light green 

 filter. The yellow in the screens helps to negative any 

 bleaching action by the ultra-violet rays. In printing by 

 the electric arc, which is richer in orange rays, a deeper 

 coloured green filter must be employed. 



In my experiments with the dyes, I found several of 

 the acid ones which could be sensitised very satisfactorily, 

 and as I was anxious to use gelatine as a vehicle instead 

 of collodion, on account of its many advantages, I ulti- 

 mately went over to gelatine emulsions altogether. I was 

 not, however, altogether dependent upon the sole use of 

 acid dyes, because in the meantime I had found that I 

 could obviate the wandering of many basic dyes out of 

 gelatine to some extent by the addition of a soluble oil 

 such as Turkey-red oil, for which these dyes have con- 

 siderable affinity. 



In order to hasten the process of printing I devised a 

 special form of printing frame (12) surrounded by four 

 mirrors which reflected the rays of the sun or arc down 

 upon the plate. To prevent the Autochrome becoming 

 overheated a constant stream of water was flowed auto- 

 matically over the surface of the plate. By this means 

 the time of printing was reduced to about one-third. 



My new bleach-out paper was placed on the market 

 in Paris, in 191 1, under the name of " Utocolor," and there 

 was always a certain demand for it until the war broke 

 out, when naturally the sales suddenly stopped. 



Very little has been published in recent years on the 

 bleach-out process. Professor Limmer (13) has published 



