532 HANDBOOK OF PHOTOGRAPHY 



2. Cause. — Subjecting the gelatin, to sudden strains through sudden changes in 

 temperature. The strain may be produced by transferring the j&lm from one sohition 

 to another at appreciable temperature difference. This condition is especially serious 

 when the solutions are warm, as in this case the gelatin swells and is then miore likely 

 to contract unevenly. 



3. Prevention. — Keep solutions between 60 and 70°F. Whenever possible, all 

 processing solutions should be at the same temperature within this limit. This may 

 be accomplished by storing the solutions side by side so that they may be exposed to 

 the same temperature variations. If it is necessary to cool solutions, all the solutions 

 required may be cooled simultaneously in the same water bath, which should be agi- 

 tated for best results. 



4. Remedy. — Reticulation may sometimes be removed by placing the negative in 

 a 10 per cent solution of formaldehyde for a few minutes and drying quickly at elevated 

 temperatures. This procedure is not recommended except as a last resort. 



White Transparent Spots. 



1. Distinguishing Characteristic. — Transparent spots, marks, or scratches on 

 the negative from which the emulsion has been removed. 



2. Cause. — Removal of emulsion from the support during processing, caused bj^ 

 gouging the emulsion with the fingernail, edge of film, or other relatively hard sub- 

 stance. This difficulty tends to increase when processing at elevated temperatures 

 when the emulsion is soft and swollen. 



3. Prevention. — Carefulness in processing, maintaining processing solutions below 

 70°F., and hardening the film before processing will all help to prevent and minimize 

 such gouge marks. 



4. Remedy. — None, except retouching negative or print. 



Scum, Slime, and Deposits 

 Crystalline Siirface. 



1. Distinguishing Characteristic. — Surface of emulsion takes on a crystalline appear- 

 ance similar to frosted windowpane or some forms of "crackle" enameling. 



2. Cause. — From crystalUzation of hypo remaining in the film after incomplete 

 washing. 



3. Prevention. — Complete washing of the negative after fixing. 



4. Remedy. — The crystals of sodium thiosulphate are soluble in water, so the nega- 

 tive may be freed from these crystals by rewashing completely. 



Greenish-white Scum. 



1. Distinguishing Characteristic. — Greenish-white scum deposited upon the sur- 

 face of the negative. 



2. Cause. — Precipitate of chromium hydroxide or of basic chromium sulphite 

 deposited on the negative when chrome alum stop or fixing baths are used. 



3. Prevention. — Use developer containing as little alkali as possible. If necessary, 

 acidify developer at intervals. Formation of scum may also be prevented bj^ agitating 

 the negative thoroughly while immersed in the stop or fixing bath. 



4. Remedy. — The scum may be removed while the negative is still wet, by means of 

 moist lintless cloth, paper, or cotton. Difficult or impossible to remove after negative 

 is dry. 



Scum. 



1. Distinguishing Characteristic. — Deposit of scum on film. 



2. Cause. — A deposit of scum on film occurs as a result of the accumulation of solid 

 matter floating on the surface of the processing solutions. It may l>e picked up when 



