INTENSIFICATION AND REDUCTION 553 



This intensifier is consequently well suited to black-and-white line work, or where 

 high contrast is desired. The silver cyanide redeveloper consists of 



Sodium or potassium cyanide (poison) 15 g. 2 oz. 



Silver nitrate 22 . 5 g. 3 oz. 



Water to make 1 1. 1 gal. 



The cyanide and silver nitrate should be dissolved separately, and the latter 

 added to the former until a permanent precipitate is just formed. After the mixture 

 has stood about an hour, it should be filtered and is then ready for use. After redevel- 

 oping, the negative is washed and dried. The intensified images are not entirely 

 permanent. 



Silver or Physical Intensifiers. — Intensification with silver, sometimes called 

 "physical intensification," produces a permanent image of neutral color. The 

 degree of intensification may be easily controlled bj'' varying the duration of the 

 intensification bath or through the use of successive treatments. Silver intensification 

 is accomplished by immersing the negative in an acid solution of silver nitrate which 

 contains a reducing agent such as metol. In this solution silver is precipitated in 

 colloidal form upon the original silver image. This colloidal silver deposits differen- 

 tially on the silver image substantially in proportion to the amount of silver in the 

 original image. Consequently all densities are increased to the same extent, and true 

 proportional intensification results. Furthermore a permanent image of neutral color 

 is obtained, since the products of the intensification are the same as those of the 

 original image. 



The following silver intensifier, taken from Crab tree and Muehler^ is more stable 

 and satisfactory than those previously recommended : 



Solution 1 



Silver nitrate 60 g. 2 oz. 



Water to make 11. 32 oz. 



Solution 2 



Sodium sulphite (desiccated) 60 g. 2 oz. 



Water to make 11. 32 oz. 



Solution 3 



Sodium thiosulphate crystals 105 g. 3.5 oz. 



Water to make 11. 32 oz. 



Solution 4 



Sodium sulphite (desiccated) 15 g. 219 gr. 



Elon (metol) 24 g. 351 gr. 



Water to make 3 1. 96 oz. 



To prepare the intensifier, add one part of solution 1 slowly to one part of solution 

 2, obtaining a thorough mixture by stirring or shaking. A white precipitate will form 

 which is dissolved by the addition of one part of solution 3. The resulting solution 

 should be permitted to stand until clear, after which three parts of solution 4 should 

 be added, with constant stirring. The film should be treated immediately in this 

 solution. This mixed solution is stable for about 30 to 45 min. at 70°F. 



The degree of intensification obtained depends upon the length of time the film 

 is immersed in the solution, but because the solution is not stable for a much longer 

 time, this should not exceed 25 min. After intensification, the film should be immersed 

 and agitated in a plain 30 per cent hypo bath for 2 min. It should then be washed 

 thoroughly. Since it has been found that hypo baths have some reducing action on 

 the silver image, the film should not be left in the hypo bath too long. 



A 50 per cent increase in density can be obtained by immersing the film in the 

 silver intensifier for 10 min., but a much higher degree of intensification may be 

 obtained through the use of successive treatments. 



