652 HANDBOOK OF PHOTOGRAPHY 



Color Prints by Dye -mordanting Process. — There are metallic compounds which 

 have a strong affinity for basic dyes. This property has been made use of for produc- 

 ing color prints on paper as well as transparencies, although the process lends itself 

 much more readily for the making of color transparencies. 



Copper mordant is very probably the most satisfactory, and it is the one used 

 extensively by Uvachrome. A satisfactory formula is one published by Namias' and 

 modified by Christensen in 1925. This can be made up in stock solution as follows: 



Stock Solution A 



Sodium citrate .37 . 5 g. 



Copper sulphate (c.p.) 3 . 4 g. 



Water 1000 cc. 



Stock Solution B 



Potassium ferricyanide 4 g. 



Water 40 cc. 



For use : 



Stock solution A 130 cc. 



Stock solution B 5 cc. 



The printing is best made on positive films and the image should be decidedly on 

 the thin side when viewed by transmitted light. With a little experience, the strength 

 of images can be readily determined. 



A satisfactory^ developer for a positive film is as follows: 



Pyrocathechin 10 g. 



Sodium sulphite 25 g. 



Potassium carbonate 25 g. 



Potassium bromide . 5 g. 



Water 500 cc. 



For use: 



Stock solution 1 part 



Water 7 parts 



Develop films until the right contrast is obtained. 



The fixing of the positive films can be carried out in an ordinary acid fixing bath 

 following by a washing for about 20 min. The positives are bleached in the mordant 

 bath made up as given above. Although the bleaching can be completed in about 4 

 or 5 min., the action should be allowed to continue for 8 or 10 min. to make sure that 

 every trace of silver has been converted. 



The positives should be washed again for about 15 min., after which each positive 

 will be passed into appropriate dye solution. Dyes satisfactory for this process are 

 the following : 



For Blue 



Methylene blue H.G.G 1 . 4 g. 



Glacial acetic acid 6 cc. 



Water 1 125 cc. 



Fob Magenta 



Pyronin red G (300 per cent) 8 g. 



Glacial acetic acid -: 12 cc. 



Water 1125 cc. 



For Yellow 



Theoflavin yellow 6 g. 



Glacial acetic acid 12 cc. 



Water 1125 cc. 



iNamias, R., La fotographia a colori, 5th ed., 11 Progresso Fotografico (1930). 



