INTENSIFICATION AND REDUCTION 559 



immediately before use. After reduction, which requires from 1 to 3 min., the nega- 

 tive should be immersed in a 1 per cent solution of potassium metabisulphite. This 

 bath will remove the stains produced by the manganese salts precipitated in the 

 gelatin. 



Superproportional Reducers.— Only a few substances produce superproportional 

 reducers, and of these the alkaline persulphates (usually ammonium) alone are of 

 practical utility. As photographic reducing agents, the persulphate reducers are 

 erratic in their behavior. Since they act more rapidly as reduction proceeds, nega- 

 tives reduced in persulphate reducers should be w^atched carefully in order that reduc- 

 tion is not carried beyond the desired degree. The reducing action maj^ be halted by 

 placing the negative in an acid fixing bath. A suitable formula is 



Water oOO cc. 5 oz. 



Ammonium persulphate 60 g. 262 gr. 



Sulphuric acid (concentrated) 3 cc. 15 minims 



Water to make 11. 10 oz. 



Because of the erratic behavior of persulphate reducers, it is best to make up this 

 solution just prior to use. The quantity of acid controls the rate of reduction. 



When the desired degree of reduction is attained, immerse the film in an acid fixing 

 bath for several minutes and then wash in clear water. If the action of this reducer 

 is too vigorous, the rate of reduction may be decreased by further dilution. 



Harmonizing. — A corrective treatment which stands midway between intensifica- 

 tion and reduction is the process commonly known as "harmonizing." Essentially 

 this process carries out intensification of shadow^ detail without affecting the high 

 lights or reduces the high lights without altering the shadows or lower densities. 

 This method is useful in treating highly contrast}'' negatives or negatives which have 

 been underexposed and overdeveloped. 



The negative is first bleached in a solution consisting of 



Potassium bichromate 8 g. 1 oz. 



Hycrochloric acid (concentrated) 6 cc. . 75 oz. 



Potassium bromide '. 5 g. 0.6 oz. 



Water to make 11. 1 gal. 



When the negative has been completely bleached, it is redeveloped in a dilute 

 developer composed of the foUowdng: 



Elon (metol) 2 g. K oz. 



Sodium sulphite (desiccated) 10 g. 134 oz. 



Sodium carbonate (desiccated) 10 g. Ijr^ oz. 



Water to make 11. 1 gal. 



Redevelopment of from 1 to 2 min. results in superproportional reduction of the 

 higher densities, but proportional intensification of the low values of density. After 

 bleaching, the negative is immersed in an acid fixing bath for 5 min., washed in clear 

 water, and dried. 



Local Intensification and Reduction. — So far consideration has been given only to 

 general intensification and reduction of the entire negative. In some cases, however, 

 it may be desired to intensify or reduce portions of the negative without affecting 

 other portions. Treatment of a portion of the negative is called "local intensification" 

 or "local reduction," and this may be highly useful in bringing out certain shadow 

 details or in reducing the density of a high light. 



Local intensification or reduction may be carried out by applying the proper 

 solution directlj^ to the negative by means of a soft camel's-hair brush. If fairly largo 

 areas must be treated, tufts of absorbent cotton saturated with the solution may be 

 preferred to the use of a soft brush. If the negative has been dried, it should be soaked 



