1901-2.] Photography in Natural Colours. 387 



screen. In the majority of cases, as will be seen later, the colours are 

 fairly true to nature, and, where such is not the case, the reason is 

 generally obvious. It must be remembered, however, in criticising 

 three-colour work that the slightest change in conditions during one 

 stage of the process may be the cause of considerable change in the 

 colours produced. Hence absolute accuracy should not be expected, 

 but a range of colours agreeing very well, in general, with the originals 

 can be, with care, always obtained. 



The three methods of negative synthesis, above referred to, follow 

 exactly the same principle. In the three-colour transparencies, part of 

 the transmitted white light is absorbed by the colours giving the 

 resultant effect. In three-colour prints on paper, whether photographic 

 or photo-mechanical, the white paper reflects all the colours, part of 

 them being absorbed by the dyes or inks in the same manner as in the 

 transparencies ; hence similar results should be obtained by the three 

 methods. 



As a matter of fact, however, leaving three-colour photographs out 

 of the question, as being not yet in a practical stage, the range and 

 gradation of colours obtained in three-colour transparencies is superior 

 to that usually reached by the three-colour photo-mechanical process. 

 The causes of this inferiority of the latter process are not far to seek. 

 In the first place, printing inks fulfilling the theoretical conditions of 

 absorption, transparency, and permanency required for this purpose 

 have not yet been produced ; and certain shades of green and brown 

 cannot be obtained by these already in use. Fugitive inks, more nearly 

 complying with the two first conditions, can be obtained giving better 

 colour renderings, but the employment of these for most purposes is 

 undesirable. In the second place, the difficulty, I think, lies in the 

 process worker trusting too entirely to empirical methods, and not 

 attempting to place his work on a true scientific basis, without which 

 complete success can not be hoped for. It is unfortunately true that 

 some soit of coloured effect can be obtained with incorrect screens and 

 printing colours, but delicate and accurate colouring is impossible with- 

 out the use of scientifically adjusted filters and colours. 



Before concluding, a short description of some of the principal 

 technical details of the process may prove of interest and possibly even 

 of s.ome service to those undertaking this fascinating branch of 

 photography. 



The first step in the process of making a three-colour transparency 



