164 PHOTOGRAPHS IN NATURAL COLORS. 



read before the Paris Academie de Science, gave full particulars of the 

 process, as follows : 



To i^repare the emulsion the following solutions are made: 



( Distilled water 400 



\ Gelatin 



Part." 

 WO 

 20 



^ Distilled water 25 



) Potassium bromide 2-3 



Distilled water 25 



itrate 3 



i Distilled wa 

 I Silver intra 



Oue-half of A is added to B and the other half to C. These two solu- 

 tions are mixed by adding the silver to the bromide. A suitable 

 sensitiser is added, such av; cyanine, methyl violet, erythrosine, etc., 

 and after tiltration plates are coated on a tourniquet at a temi)erature 

 of 40O C. 



When the emulsion is set the plate is immersed in alcohol for a very 

 short time, and washed in a continuous stream of water. The film 

 being very thin the washing is soon effected. This emulsion should not 

 be washed in bulk, lest coarseness of the particles of silver produced 

 by re-heating results, and in order to leave the films as transparent as 

 possible; for the same reason an excess of bromide is to be avoided. 

 The plates are dried, and just before use are immersed for 2 minutes in : 



Parts. 



Water 200 



Silver nitrate 1 



Acetic acid 1 



This bath helps to produce brilliancy of the image, and to increase 

 the sensitiveness. But the plates cannot then be kept long, because 

 the sensitive surface soon deteriorates. When the plate is dry, it is 

 ready for exposure a la Lippmann, viz, with a reflecting surface next to 

 the film. 



For the developer the following solutions are made: 



Parts. 



Part.s. 



Sol. I 10 



Sol. II 15 



Sol. Ill 5 



Water 70 



J I) Water 100 



I Pyrogallic acid 1 



J J (, Water 100 



' Potassium bromide 10 



j^y ) Ammonia D. 



'( 0-960 diluted to 18^ 



The degree of concentration of the ammonia has a great intluence on 

 the result, even a slight alteration destroying the brilliancy of the 

 colors. For fixing, the plate after washing is immersed for from 10 to 

 15 seconds in a 5 per cent, solution of potassium cyanide, washed and 

 dried. 



In order to lessen the action of the ultra-violet, violet, and blue 

 rays, a parallel faced batll pf Victoria yellow, ur^^nio or primuliuc is 

 used iu the camera/, 



