COLOR PHOTOGRAPHY 645 



washed for 10 or 15 min. to completely remove any trace of bichromate, after which 

 they can be stained immediately in the appropriate dyes or allowed to dry as before. 

 If it is considered desirable to remove the silver image before staining with dye, this 

 can be readily carried out with regular Farmer's reducer. 



The advantages to be derived bj^ using the positive transparencies for dye printing 

 are as follows: Since the exposure to the light has taken place through the back, the 

 degree of relief is extremely small and the successive stainings take place in a much 

 more uniform manner, as compared with the previous method. The contact with the 

 final paper is a good deal more intimate and the delicate details are retained a great 

 deal more faithfully than with the straight Pinatype method. 



With both methods, however, positive films can be used to advantage in place of 

 glass plates, as the squeegeeing operation can be carried out much more easily. 



Dyebro Process. — Relief images on thin celluloid supports can be produced also 

 by the carbro method. The only deviations from the standard carbro method are as 

 follows: Instead of trichrome tissues, an appropriate gray tissue with very slight 

 coloration is being used. All the various operations, however, are strictly identical to 

 the previouslj^ described carbro process. After being made insoluble in contact with 

 bromide papers, the tissues are transferred to the celluloids, without any waxing, and 

 developed in hot water as usual. 



The staining of these reliefs, the final transfer paper, and the method of dye trans- 

 fer is strictly identical with the Eastman wash-off relief. The carbro reliefs on the 

 thin, transparent celluloids should be given an additional final hardening in a 5 per 

 cent solution of formaldehyde, before staining, to increase their durability. 



Chemical Toning Processes. — A positive silver image can be converted into a 

 colored image by replacing the silver of the image by means of metallic compounds. 

 Methods for producing satisfactory blue and yellow tones have long been known, but a 

 satisfactory magenta image by chemical toning has been made available only 

 recently by Defender and the complete process marketed under the trade name 

 Chromatone. 



By this process, prints from the three color-separation negatives are made on a 

 special paper from which the image can be stripped and transferred in register to a 

 final support. The emulsion of the printing paper is carried by an extremely thin 

 collodion sheet which detaches from the paper base during the washing operation. 



Three developers are recommended for use with the Chromatone printing paper, 

 depending on the nature of the original three color-separation negatives. 



Standard Formula 1 — For Prints from Normal Negatives 



Water 40 oz . 2000 cc. 



Metol 51 gr. 1 . 5 g. 



Sodium sulphite (dry) . 5 oz. 22 . 5 g. 



Hydroquinone ! 60 gr. 6 . 5 g. 



Sodium carbonate (dry) . 5 oz. 22 . 5 g. 



Potassium bromide 25 gr. 2 . 7 g. 



Development: 1^9 min. at 70°F. 



Formula 2 — For Good Prints from Hard Negatives 



Water 32 oz. 1000 cc. 



Metol 44 gr. 3 g. 



Sodium sulphite (dry) 1 oz. 88 gr. 36 g. 



Sodium carbonate (dry) 263 gr. 18 g. 



Potassium bromide 58 gr. 4 g. 



For use, one part stock solution, three parts water, and develop 3 to 4 min, at 70°F. 



