554 HANDBOOK OF PHOTOGRAPHY 



Reduction of the intensified image may be accomplished by the use of such sub- 

 tractive reducers as Farmer's and Belitzski's reducers. These reducers do not affect 

 the contrast of the intensified image. Suitable formulas giving proportional reduction 

 with the silver image have not been developed to date, so that the desired contrast will 

 have to be determined in the intensification process. 



Uranium Intensifier. — Uranium intensification produces an extremely high degree 

 of intensification 1 primarily because of the color of its'image, which varies from reddish 

 brown to bright red. A disadvantage of uranium intensification is that the photo- 

 graphic intensification is considerably greater than visual intensification, so that the 

 desired effect may be difficult to judge. Moreover, the intensified image is not com- 

 pletely permanent. Because of the high intensification produced, the method is 

 suitable for use wdth very thin negatives where other intensification methods might 

 be unsuitable, or it may be used as a local intensifier. 



A suitable uranium intensifier may be made with the following two solutions: 



Solution 1 



Potassium ferri cyanide 50 g. 384 gr. 



Water 11. 16 oz. 



Solution 2 



Uranium nitrate 50 g. 384 gr. 



Potassium bromide 20 g. 154 gr. 



Water •. 1 1. 16 oz. 



Immerse the negative in solution 1 until bleached, then wash thoroughly in water. 

 Immerse in solution 2 until no further action takes place, and wash in a dilute bath of 

 acetic acid. Finally wash in plain water, and dry. 



Because of the change in color produced, uranium intensification is sometimes 

 considered as a toning process. 



REDUCTION 



Photographic reduction is the process by which the effective density of the photo- 

 graphic deposit is diminished. Reduction of the photographic image may be desirable 

 for several reasons: (1) It may be desired to diminish the average density of the nega- 

 tive so that the printing time may be reduced; (2) reduction may be used to increase or 

 decrease the contrast; (3) traces of fog may be removed by reduction; (4) effects of 

 overexposure or overdevelopment of a positive image may be modified by reduction. 



The process of reduction consists in dissolving away some of the silver deposit of the 

 image. Depending upon the differential action of the reducing agent on the density 

 of the original silver image, the effect of photographic reduction varies with the type 

 of reducer employed. This gives rise to the following convenient classification of 

 photographic reducers: 



Types of Reducers.— Subtractive reducers are those which remove an equal amount 

 of silver from all parts of the image or from all densities. Through their use the gen- 

 eral or mean density of the negative is diminished but the density range (and con- 

 sequently the contrast) is usually increased. Subtractive reducers are used mainly to 

 improve overexposed negatives and positives, or for the removal of fog. Subtractive 

 reducers are also known as "cutting" or "surface cutting" reducers. 



Proportional reducers are those which remove the silver deposit in proportion to 

 the amount originally present in the image. Thus, all densities are reduced by the 

 same percentage, and contrast is decreased. Proportional reducers are used mainly 

 to reduce excessive density and contrast due to overdevelopment. 



Superproportional reducers remove a greater percentage of silver from the high 

 densities than from the low. Accordingly the decrease in density due to reduction is 



1 NiETz and HuSE, Phot. J., 68, 81 (1918); J. Franklin Inst., 185 (No. 2), 231 (1918). 



