322 THE ORCHID REVIEW. 



the question has been asked how far the process has come within the 

 range of practicability ? The answer is somewhat difficult, for there 

 are technical difficulties involved, but we have seen pictures of Orchids 

 which, if not exact reproductions, were quite unmistakable. A recent issue 

 of Le Jardin (August 5 th) contained two " photochromogravures " showing 

 combinations of Oncidium Marshallianum, Odontoglossum crispum, and 

 Cattleyas, with graceful foliage plants, which were exceedingly effective 

 and show the possibilities of the system. And we believe that the 

 difficulties at present encountered will be overcome in course of time. 



The pictures mentioned are obtained thus. Half-tone blocks of the 

 three positives before mentioned are made, and these are printed in their 

 own proper colours, and in correct register. The positive prepared from 

 the photograph taken through the violet screen is printed in yellow, that 

 through the green screen in pink, and that through the red screen 

 in cyan-blue. They are printed thus: First the yellow, then the 

 pink impression upon the yellow, and finally the blue impression 

 upon both; which reproduces the original picture. The combined 

 print is often a very pleasing reproduction of the original, but there is 

 a granular appearance about it (due to numerous minute dots) which 

 detracts from its beauty. This, however, is absent from reproductions 

 m collotype. A greater difficulty is at present encountered in obtaining 

 colours which are at once permanent and of the exact shade required. For 

 example, the only colour which gives approximately the correct shade of 

 pink is rhodamine, one of the coal tar colours, but, unfortunately, it fades 

 in a few hours, and the nearest substitute which is permanent does not 

 give an absolutely correct result. Truth of form it achieves absolutely, 

 and the defects of the system are due to the mechanical difficulty of 

 applying an absolutely correct theory. When proper pigments are used, 

 with correct registration, the results are almost beyond criticism, and 

 if such a high standard has not at present been uniformly attained it 

 is likely that the difficulties will be overcome in course of time. 



It may at first appear difficult to understand why the separated violet 

 rays should be printed in yellow, the green rays in pink, and the red rays 

 m blue, but the explanation is as follows :— To take the yellow first. 

 Yellow is made up of red and green colour sensations in the absence of violet, 

 and therefore a clear yellow patch in the orginal object would contain no 

 violet rays. But this same yellow patch would pass its 50 per cent, of 

 green rays through the green screen, and its 50 per cent, of red 

 rays through the red screen, these being recorded in the resulting 

 negatives. Similar remarks apply to the selective influence of the colour 

 screen, upon the other two kinds of colour sensations, red and green. But 

 the resulting negatives cannot be combined at this stage, for the result 



