COLOR PHOTOGRAPHY 655 



process of having to split up the Hght source, this process is invariably thrown into 

 discard. 



In the case of single transparencies to be viewed visually, the so-called "screen 

 plates" and films in which the three-color filters are incorporated with the emulsion 

 in a regular or irregular pattern, a fairly high degree of success has been achieved. In 

 this class can be listed the Lumiere Autochrome plate and Filmcolor, and the Agfa 

 color plate. These three types carry the color filter elements coated on the support 

 in irregular mixture of very small transparent elements, stained with the three primary 

 colors. On this color screen layer, there is a protective coating and then the pan- 

 chromatic emulsion. The exposure of these plates or films is made through the 

 supports. 



The processing of screen plates or film is very simple and consists in first developing 

 the original exposure, and then, without fixing, the developed silver image is removed 

 by a suitable bleach. The balance of emulsion, which" was not affected by the first 

 development, is exposed again to a white light and redeveloped, resulting in a final 

 positive image. 



The reversal process, in order to be satisfactory, requires that the original exposure 

 be kept within fairly narrow limits in order to leave sufficient emulsion to later produce 

 the positive image. The development also must be carefully carried out as very little 

 latitude is permissible. 



The manufacturers of these materials iss\ie complete instructions to be found 

 included in each package, and it is strongly recommended that these instructions be 

 carefully followed. 



In order to permit an exposure under different light conditions, suitable com- 

 pensating filters are necessary; these filters can be obtained commercially from the 

 manufacturers. To assure correct results, compensating filters appropriate to each 

 light source must be used in accordance with the manufacturer's instructions. 



Agfa Screen Plate. — The following instructions in condensed form cover the process- 

 ing of the Agfa color plate, and for additional informations the reader should refer to 

 the instructions supplied with the negative material. 



First Developer 



Water 1000 cc. 



Metol 3 . 25 g. 



Sodium sulphite (dry) 25 g. 



Hydroquinone 1 g. 



Potassium bromide 1.5 g. 



Ammonia (spec. gr. 1.91) 7.5 ce. 



For a correctly exposed plate, the normal time of development will be approxi- 

 mately 3 min. at 65 °F. About 2 oz. of the above developer will be necessary 

 to develop a 3^^- by 414-in. plate. For larger plates the quantity of developer should 

 be increased in proportion. This developer can be used also for second development, 

 but, as it loses strength by the evaporation of ammonia, it should be discarded after 

 the second development. 



When the first development is complete, the plate should be rinsed for about 1 

 min. in a large tray of water, or running water if it is conveniently at hand, and then 

 immersed in the reversing bath made up as follows: 



Water 900 cc. 



Potassium bichromate 50 . 6 g. 



Sulphuric acid (c.p.) 1 10 cc. 



This is a stock solution; for use take 1 part solution to 10 parts water. 

 A few seconds after the plate has been immersed in the reversing solution, Mie white 

 light can be turned on and the processing continued under normal white light. The 



