DEFECTS IN NEGATIVES AND PRINTS 529 



(d) chemical or other dust floating on surface of developer; or (e) a solvent of free 

 silver acting on the negative after development. 



3. Prevention. — (a) See Microscopic Spots, page 527. (b) See Air Bells, page 523. 

 (c) See Small Circular Spots, page 528. {d) Make sure that developer is free from 

 undissolved particles or other foreign matter. Particles which have gathered on the 

 top as scum may be removed by means of a wire frame covered with cheesecloth or bj' 

 patting the top of the solution with an absorbent cloth. Filtering the solutions is 

 also helpful, (e) Cleanliness and protection of the negative from chemicals other 

 than those intended to act upon it will prevent the last-mentioned defect. 



4. Remedy. — None. 



Yellow Spots. 



1. Distinguishing Characteristic. — Yellow spots, circular in shape, with fairh' 

 sharply defined edges. 



2. Cause. — Air bells or bubbles in the fixing bath. 



3. Prevention. — Agitate negative and developing solution. Remove air bells by 

 bi-ushing the surface of the negative with soft brush during fixing. 



4. Remedy. — If observed after negative has just been fixed, they may be removed 

 by brushing off air bells and refixing. 



Water Spots. — (See Drop Marks, page 525.) 



Mechanical Defects and Injuries 



Under this heading are listed those defects and injuries in which the negative 

 fails to meet the normal mechanical or physical requirements or in which the negative 

 is mechanically damaged. These defects may be in addition to other defects which 

 are given in this chapter. 



Blisters. 



1. Distinguishing Characteristic. — Emulsion raised from the gelatin, when the 

 negative is wet with an appearance similar to blisters of the flesh. After the negative 

 has dried, blisters appear as small craterlike depressions in the emulsion. 



2. Cause. — Blisters are caused by gas pockets forming between the emulsion and 

 the film support due to loosening of the gelatin as a result of (a) permitting wash 

 water to fall directly on the emulsion side of the negative ; (6) processing solutions too 

 warm; (c) developing or fixing bath too concentrated; or {d) insufficient rinsing of the 

 negative after developing, especially if this is followed by placing negative in a 

 strongly acid fixing bath. The blisters are produced by the formation of carbon 

 dioxide gas during processing especially at relatively high temperature when the 

 gelatin is too soft to withstand the disruptive effect of the gas. Carbon dioxide is 

 evolved when the sodium carbonate of the developer is neutralized by the acid in the 

 fixing bath. Tendency toward the formation of blisters is increased during hot 

 weather, when the processing solutions are too warm, and when the film is not suffi- 

 ciently hardened. 



3. Prevention. — (a) Do not permit wash water to fall directly on negative with 

 appreciable force. (6) Solutions should not normally be at a temperature exceeding 

 70°F. unless the negative is hardened and tropical development is being used, (c) 

 Using solutions at their normal concentration and temperature will help prevent 

 formation of blisters, {d) Washing the negative in clear water between developing 

 and fixing will remove most of the developer so that the tendency toward the for- 

 mation of carbon dioxide is diminished when the negative is placed in the fixing bath. 



