EXPOSURE, DEVELOPMENT, ETC.
Screens or colour filters of the three correct tints are obtainable, generally consisting of thin stained films of gelatine or collodion, enclosed between two glasses. The exposure has to be care fully proportioned, so that each colour receives a due amount of time. Mr. A. Watkins suggests that a useful aid to this is to include a small patch of white in the object, which should be developed to equal density in the three negatives. Softness and delicacy should be aimed at, or the colours will be too glaring and crude in the final result. The negatives are developed and finished in the ordinary way, except that, as they are abnormally sensitive to all colours, the operation must take place almost in the dark. Three positives are then made from the three negatives, in just the same way as com monly pursued in making lantern slides. Up till now, these positives appear to present nothing unusual ; it is only on looking at them, as thrown together in a special manner by an ingenious instrument called a " Kromskop," or Photo-chromo scope, that the colours of the original are correctly interpreted.
How THE COLOURS ARE RECORDED.
It has been seen that there are three transparencies, answering respectively to the ed, green, and blue-violet portions of the subject photographed. In the Krom
skop these are viewed through red, green, and violet glasses, the three images being thrown at the same time into one. This will be better understood by reference to Figs. 570 to 575, which show the three negatives and transparencies obtained from a simple object, selected for the purpose of illustration. Fig. 560 repre sents the original, consisting of a violet cross on a red shield, the surrounding ground being green. Figs. 570, 571, and opaque patch. It is perfectly evident, i therefore, that when the transparencies ,! are all viewed at once through glasses of suitable colours, a correctly tinted repro- I duction of the original will be seen. Corn I pound colours, of course, will be re presented on two or even three of the transparencies, and will be truthfully ' 572 show the red, green, and blue-violet negatives obtained from such a subject ; while Figs. 573, 574, and 575 show the shown by the combination of the required component colours, in the requisite pro portions.