G58 HANDBOOK OF PHOTOGRAPHY 



The exposure to white Hght can be omitted if the second developer i,s replaced hy 

 the following chemical reversal bath: 



Water 1000 cc. 



Sodium hydrosulphite 14 g. 



Sodium bisulphite 10 g. 



One minute of treatment will be sufficient. This bath does not keep and it must 

 be made up just before use. 



Following the second development or reversal the film must be again washed for 

 2 or 3 min. and fixed in a hardening bath made up as follows: 



Water 1000 cc. 



Hypo 360 g. 



Potassium metabisulphite 12 g. 



Dissolve separately: 



Water 1000 cc. 



Chrome alum 10 g. 



This should be added to the first solution. P'ixing should be followed by a final 

 wash for about 15 min. 



Dufaycolor film also can be intensified and reduced. The following mercury 

 intensifier is recommended: 



Water ■ 1000 cc. 



Mercury bichloride 65 g. 



Ammonium chloride 50 g. 



The film should be left in this bath until entirely white. This requires 3 or 4 min., 

 followed by washing in running water for about 15 min., after which the emulsion 

 should be blackened in a solution as follows: 



Water 1000 cc. 



Sodium sulphite (dry) 50 g. 



The action of the sodium sulphite can be stopped when the right degree of intensi- 

 fication has been obtained. 



A suitable reducing formula for Dufaycolor film follows: 



Solution A 



Water 1000 cc. 



Potassium ferrieyanide -10 g. 



Solution B 



Water 1000 cc. 



Hypo 200 g. 



For use take equal parts of A and B and dilute with 10 parts of water. After 

 sufficient reduction, the films should be thoroughly washed in running water. 



Although it is satisfactory to intensify the Dufaycolor film to increase the bril- 

 liancy, the reduction is not recommended, and it is best to calculate the original expo- 

 sure correctly by means of an exposure meter. 



To make color-separation negatives from Dufaycolor film for color prints on paper 

 by any of the subtractive processes previously described, sharp cutoff filters must be 

 used. The filters recommended for this purpose are the Dufay separation filters, 

 although satisfactory results can be obtained by using for the red the Wratten 25 plus 

 33; for the green Wratten 52 plus 58; for the blue Wratten 34 plus 47. 



Very satisfactory duplication of Agfa color plates, Lumiere Autochrome plates and 

 films, and Dufaycolor films cannot be made. When an original subject is to be photo- 



