INTENSIFICATION AND REDUCTION 



655 



proportional to the amount of silver originally present in the image. Such a reducer 

 decreases the contrast and is used chiefly for the reduction of overdeveloped negatives 

 of contrasty subjects. 



Superpropor+ionoil 

 Reduc+ion 



Fig. 3. — Characteristic curves of original and reduced photographic materials for various 



types of reducers. 



Sensitometry of Reducers. — The characteristics of reducing agents may be deter- 

 mined in exactly the same manner as the 

 characteristics of intensifiers are determined, 

 and the results may be plotted in the same 

 form. Figure 3 shows the D-logio E charac- 

 teristics of an assumed photographic 

 material, together with hypothetical charac- 

 teristics of the three idealized types of 

 reducers. Figure 4 shows the character- 

 istics of reducers plotted in such a way that 

 their classification is somewhat more readily 

 recognized. In Fig. 3, curve A represents 

 the subtractive reducer, curve B the pro- 

 portional reducer, and curve C the superpro- 

 portional or "flattening" reducer. These 

 three types of reducers, as may be seen from 

 Fig. 4, maj^ be labeled as positive-gradient, 

 zero-gradient, and negative-gradient reducers, corresponding, respectively, to super- 

 proportional, proportional, and subproportional reducers of Fig. 3. 



According to this classification, the following three types of reducers together with 

 representative formulas are permissible: 



1. Superproportional or positive-gradient reducers 

 Farmer's reducer 

 Haddon's reducer 

 Iodine-cyanide reducer 

 Ferricyanide and cyanide reducer 

 Modified Belitzski reducer 

 Potassium permanganate reducer 

 Bichromate reducer 

 Ceric ammonium nitrate reducer 

 Ceric ammonium sulphate reducer 

 Ferricyanide and ammonium sulphocyanide 



Original Densi-hy 

 Fig. 4. — The characteristics of vari- 

 ous types of reducers, expressed in per- 

 centage change of the original density. 



