536 HANDBOOK OF PHOTOGRAPHY 



Green Dichroic Stain. 



1. Distinguishing Characteristic. — Green metallic sheen by reflected light and red 

 or pinkish color by transmitted light. 



2. Cause. — (See Dichroic Fog, page 517). 



3. Prevention. — (See Dichroic Fog, page 517). 



4. Remedy. — (See Dichroic Fog, page 517; also see page 165, Motion-picture 

 Laboratory Practice 1936.1 



Green Stain. 



1. Distinguishing Characteristic. — Negative has appearance of being dyed green: 

 occurs in stop bath. 



2. Cause. — Stain appearing in stop bath is a function of the relative amounts of 

 carbonate and sulphite in the developer and the concentration of the chrome alum in 

 the stop bath, and it increases with increasing temperature of solution. 



3. Prevention. — Properly compounded and fresh processing solutions maintained 

 at a temperature not exceeding 70°F. 



4. Remedy. — Usually this green stain can be removed by immersing the film in a 

 5 per cent solution of potassium hydroxide or 5 per cent solution of potassium citrate. 

 This treatment destroys the hardening properties of film negatives. 



Purple Stain. 



1. Distinguishing Characteristic. — Purple discoloration on negative. 



2. Cause. — (a) Purple stains may be due to presence of iron in the water used in 

 making up processing solutions, (b) This stain occurs frequently in the fixing bath if 

 negatives stick together so that complete fixing cannot be accomplished. The stain 

 occurs where the negatives make contact, because of the continuance of developing 

 action in the fixing bath. 



3. Prevention. — (a) Use of distilled or at least filtered water for making up process- 

 ing solutions will assist in removing iron particles. (6) Agitation of negatives in 

 fixing solution. 



4. Remedy. (See remedy under Bhie Stains, page 534.) 



Silvery-white Opalescence. — (See Yellowish-white Opalescence, below.) 

 Stains from Ferricyanide. 



1. Distinguishing Characteristic. — Green or blue discoloration. 



2. Cause. — Sometimes caused when ferricyanide reducer is employed. 



3. Prevention. — -Do not use ferricyanide reducers. 



4. Remedy. — Immerse negative, until stain is removed, in a solution of 6 cc. of 

 nitric acid and 6 g. of alum per liter of solution. Wash in clear water and dry. 



Yellowish -white Opalescence. 



1. Distinguishing Characteristic. — -Yellowish white or silvery white opalescence 

 on part or all of the emulsion, suggestive of opal. 



2. Cause. — This opalescence may be due to: (a) incomplete fixing; (b) use of alcohol 

 to hasten drying; (c) drying rapidly in warm air; (d) excessively high temperature of 

 fixing bath; or (e) presence of colloidal sulphur in improperly compounded fixing bath 

 containing excess acid. 



3. Prevention. — (a) Complete fixing with properly compounded, fresh fixing batt, 

 (6) When alcohol is used to hasten drying, it should be diluted with water to give a 

 solution having 80 per cent alcohol, (c) Dry negative less rapidly in atmosphere of 

 from 40 to 70 per cent humidity and at a temperature not exceeding 90°F. (d) The 



