372 HANDBOOK OF PHOTOGRAPHY 



n'<'oni mended as leading to best results, but the formulas are probably as near general 

 applicabilit}'' as any. 



High-temperatiire Processing.— When processing is to be done under conditions 

 such that it is impossible to keep the solutions from becoming warm, 80°F. or above, it 

 is usually necessary to take special precautions to keep the gelatin from softening too 

 much. Hardening agents may be used as prebath; H P^r cent formaldehyde solution 

 may be used for this purpose. 



A second method of meeting the situation is to use the developer loaded with 

 chemicals which tend to reduce the swelling of gelatin. Sodium sulphate is most 

 frequently used, though the sodium sulphite of the developer also tends to reduce 

 swelling. Sodium sulphite concentrations in from 100 to 200 g. per 1. protect the 

 gelatin greatly in warm solutions. Developing times should be kept as short as pos- 

 sible, and development should be followed immediately by a hardening stop bath and 

 good fixing bath with the shortest wash which will eliminate the hypo. 



No. 21 For High Temperatures 



Sodium sulphite (anhydrous) 50 g. 6 oz. 290 gr. 



p-Aminophenol hydrochloride 7 g. 405 gr. 



Sodium carbonate (monohydrated) 60 g. 8 oz. 



Sodium sulphate (crystals) 100-200 g. 13 . 3-.26 . 6 oz. 



Water to 11. 1 gal. 



Development can be carried out up to 95°F. The development time varies with 

 the sulphate concentration. Times of tjae order of 1}^ min. may be expected with the 

 lower concentration and of the order of 3 min. with the higher concentration indicated. 



Reversal Development. — In reversal processing several special formulas have been 

 worked out. The requirements are somewhat different than in direct development 

 for other purposes. The first development of a reversal process must develop essen- 

 tially all the silver which was rendered developable by the first exposure. In some 

 cases a fog is intentionally developed to secure the desired characteristics from the 

 emulsion in use. The characteristics above are often secured from the normal devel- 

 oper constituents, but in addition to these, weak silver halide solvents are sometimes 

 introduced to (1) insure clear high lights or (2) reduce the tendency to brown tones. 

 In both cases, the effectiveness of the procedure is at least in part due to the fact that 

 the solubility of small grains is greater than of large. These small grains are in general 

 slow, so they would be the ones least affected by first exposure and therefore most 

 likely to remain to veil high lights on second development. These small grains are 

 also the ones which would be expected to impart a brown tone to the final image. 

 These effects are not large and startling and probably differ in importance with differ- 

 ent emulsions, but the use of silver halide solvents in reversal development has been 

 important in some cases. The silver halide solvents used vary from hypo itself as a 

 very active solvent to potassium thiocyanate as a weak solvent. 



No. 22 Reversal First Developer 



Sodium sulphite (anhydrous) 50 



Rhodol (metol or Elon) 1 



Hj'droquinone 8 g. 



Sodium carbonate (monohydrated) 35 g, 



Potassium bromide 5 



Potassium thiocyanate 9 



Water to 11. 



Development times may be expected to lie in the range from 5 to 8 min. at 65°F. 

 All steps of exposure and reversal processing have to fit together closely to form a 

 complete reversal system designed to conform to the individual stock processed, hence 

 no very exact figures can be given in this rather general discussion. 



