COLOR PHOTOGRAPHY 639 



yellow image. The two are withdrawn together and laid on a sheet of plate glass 

 with the paper support uppermost. The flat squeegee can be applied gently to the 

 sandwich to remove the excess of gelatin solution, after which the sandwich can be 

 reversed right side up and a final registration carried out by gently sliding the celluloid. 

 When a satisfactory registration is accomplished, the sandwich can be hung up to dry. 

 Occasionally it may be necessary to bend the celluloid to secure accurate registration, 

 particularly after the paper support with the yellow image has been soaked too long 

 in the water. This, however, should not be necessary if the soaking of the paper 

 support is not carried out beyond Wi min. 



Instead of a fiat squeegee the surplus gelatin solution can be forced out by applying 

 a dry cloth over the back of the paper support. When dry and the celluloid is 

 detached leaving the red and yellow images together, the image surface is again 

 cleaned free of wax in the same manner as before and the blue-green image transfer 

 carried out in exactly the same manner. 



Double Transfer. — The double-transfer method has many points of advantage, 

 and it is highly recommended in preference to the single-transfer method. It is very 

 difficult to register the red to the yellow image, particularly if the transfer has to be 

 carried out with incandescent light, for the yellow image is almost invisible with 

 artificial light. With the double-transfer method, however, the blue-green image is 

 first transferred to a temporary support which consists of soluble gelatin on a thin 

 paper base. With a soluble temporary support it is not necessary to use the gelatin 

 solution as recommended for the single-transfer method. The removal of the wax 

 after each transfer should be carried out in the same way as previously described. 

 The sequence of transfer with the double-transfer method is blue-green image first, 

 then the magenta image, and finally the yellow image on top. It will be found very 

 easy to register the yellow image by this method. The wax must be again removed 

 from the yellow surface after the three transfers are complete. 



The temporary soluble support with the complete color image is now placed again 

 in cold water and brought into contact with the fuial paper support which could be 

 also a fixed-out bromide paper or regular single-transfer paper available commercially. 

 The two are squeegeed together with a flat squeegee and placed under pressure 

 between blotting papers for 15 or 20 min. The sandwich is finally placed into hot 

 water at 100°F., and after 1 or 2 min. the paper backing of the temporary soluble sup- 

 port can be readily stripped, leaving the complete image on the final support. The 

 soluble gelatin left by the temporary support can be gently washed off, and the com- 

 plete picture is put away to dry. 



By the double-transfer method it is possible to trim the temporary support, with 

 the color image on it, down to the exact size of the latter, but if this procedure is 

 followed it is necessary to allow the soluble support to remain in contact with the final 

 paper until completely dry. When this is done, the stripping of the paper support in 

 hot water should be preceded by a bath in cold water for 10 or 15 min. Unless this 

 precaution of drying the sandwich first is taken, there is a danger of the image frilling 

 and becoming damaged because of lack of the safe margin which was removed by the 

 trimming operation. 



With the double-transfer method the bromides must be printed right side up. 



Concluding Remarks. — In carrying out a carbro process great care must be 

 exercised to avoid contamination with the usual darkroom chemicals. Developing 

 chemicals have a tendency to bleach the blue tissue, and therefore if small circular 

 white spots occur in a blue tissue, these can invariably be ascribed to traces of devel- 

 oper. These spots ordinarily disappear in a span of 24 hr. Their disappearance, 

 however, can be expedited by treating gently the finished color picture, locally, with a 

 weak solution of hydrochloric or acetic acid. 



