io J. H. Smith, Bleach-out Process of Colour Photography. 



this way I have employed so many as eight or ten, and 

 even more dyes in an emulsion with advantage. I am, 

 in fact, of opinion that a series of six dyes, one set of the 

 three primaries and another set of the three secondary 

 colours, would be preferable to a series of three colours 

 only, if they could be found with the necessary properties. 

 Fig. b, on the coloured plate, shows the bleaching action 

 on a film containing six dyes in place of three when 

 exposed under a coloured original to print. 



I am quite aware that there would be some degrada- 

 tion of colour by the use of the primaries where their 

 mixtures are concerned, but if they were selected to 

 transmit two-thirds of the visible spectrum as the comple- 

 mentaries have to do, and not only one-third as is 

 required in the screen colours of the Autochrome plate 

 or in the screens for three colour photography, the degra- 

 dation of colour would not be so appreciable, and the 

 defect would be more than compensated by the purity 

 of the colours and their immunity from bleaching at 

 seven points of the spectrum instead of only at four 

 points (the pink being supposed to be represented by the 

 overlapping of the extreme ends of the visible spectrum). 



I cannot claim that in practice the increase in the 

 number of dyes I employed was even an approximation 

 to these theoretical conditions, as I had to consider in the 

 first place the correction of the defects of my chief dyes 

 by supplementary ones. 



In my endeavours to increase the sensitiveness of the 

 paper I discovered in thiosinamine a new sensitiser which 

 possessed many valuable properties. It sensitised for 

 many dyes twenty times more energetically than anethol, 

 the most active sensitiser known up to that time. It 

 possessed the further advantages of being easily soluble 

 in water and in alcohol, thereby being easily removable 



