COLOR PHOTOGRAPHY 657 



light sources. The processing also is carried out in an essentially similar manner: 

 i.e., first development, followed by a bleach, and a second development. 



For the Dufaycolor film the following method of processing is recommended; 



First Developer 



Water 100 cc. 



Metol 1 g. 



Sodium sulphite (dry) 50 g. 



Hydroquinone 8 g. 



Sodium carbonate (dry) 35 g. 



Potassium bromide 5 g. 



Potassium thiocyanate 9 g. 



The time of development may vary from 4 to 6 min., according to the amount of 

 exposure, at about 68°F. 



After a brief rinse in water, the Dufaycolor film is passed into a bleaching bath 

 made up as follows: 



Water 1000 cc. 



Potassium bichromate 5 g. 



Sulphuric acid (commercial grade of sp. gr. 1.87) 10 cc. 



The bleaching will be completed in about 4 min., after which the film can be given 

 a brief wash for about 2 min. and then immersed in a clear bath composed of 



Sodium bisulphite 25 g. 



Water 1000 cc. 



This immersion lasts for about 2 min.; the film is again washed for 2 or 3 min. 

 The purpose of the clearing bath is to remove any yellow .stain of potassium 

 bichromate. 



After the film has been immersed in the bleaching solution, the white light can be 

 turned on and the bleaching completed in diffused white light. 



For second development any MQ developer can be used, the following being 

 recommended : 



Water 1000 cc. 



Metol " 1 g. 



Sodium sulphite (dry) 50 g. 



Hydroquinone 5 g. 



Sodium carbonate (dry) 20 g. 



Potassium bromide 1 g. 



The bleaching of the film can be carried out with a solution of potassium per- 

 manganate instead of bichromate. The following is a suitable solution: 



Water 1000 cc. 



Potassium permanganate 3 g. 



Sulphuric acid (specific gravity 1.87) 10 cc. 



The bleaching in permanganate, however, must be preceded by a brief treatment 

 in the following hardening bath to avoid frilling: 



Water 1000 cc. 



Formalin (40 %) 28 cc. 



Sodium hydroxide 1 . 5 p;. 



Sodium sulphate 150 g. 



The exposure to light after bleaching can be done with incandescent light instead 

 of diffuse daylight. One minute of exposure at a distance of 12 in. from a 100- watt 

 lamp will be found sufficient. 



