TECHNIQUE OF DEVELOPMENT 361 



appear to give greater uniformity of results than inspection methods, though these are 

 also widely used. Some difference of opinion exists as to the best method, and perhaps 

 there is no general answer. After all is said and done, there is the question of retakes, 

 and it may be best to make a fair quality radiograph by minor development compensa- 

 tion for an exposure variation, rather than to insist on hewing to the line of complete 

 uniformity of development, let the retakes be what they may. This is not written in 

 the spirit of condoning careless work, for pressure for quality is a continuous necessitj'. 

 No major changes of development time from standard can be tolerated without being 

 reflected in poor quality of some of the radiographs. 



Motion-picture Film. — The commercial methods of control are largely based upon 

 sensitometric and test-exposure control, as indicated before. Inspection methods 

 are in use in some of the smaller units. If many scenes are on one roll, individual 

 development treatment is manifestly impossible, but the roll may be treated as a unit 

 to give the best average as judged by the experience of the worker. 



Defects in Development. — Many defects in the final pictures are traceable to 

 development difficulties. Some of these are similar to defects from other causes and 

 accordingly both will be mentioned with an indication of some of the distinguishing 

 characteristics. 



White spots are produced by several different causes in processing, and, in addition 

 to these troubles, they may be caused by lint or dirt on the original emulsion surface 

 which frequently leaves enough of a shadow outline to be suggestive of the natui'e of 

 the particle causing the difficulty. White spots in a print caused by black spots in the 

 negative are usually readily identified by careful inspection of the negative. 



Of the group traceable to processing, primarily development, the following are the 

 most common: 



Ail- Bells. — Air bells are often formed as the plate, film, or paper is placed in the 

 developer. They take the form of small bubbles clinging to the emulsion surface and 

 may stay throughout the entire time of development unless dislodged by mechanical 

 means. They are more common in stagnant or weakly agitated developments, as 

 thorough agitation supplies the forces necessary to dislodge them. When motion- 

 picture film is developed by the rack and tank system, air bubbles are almost always 

 formed on the lower bar of the rack and are very apt to remain there for it requires 

 special care in agitating the rack to dislodge them. However, they may occur under 

 many other conditions of development. 



When the air bell is not dislodged, the developer can penetrate under it only by the 

 relatively long path through the surrounding emulsion, thus effectively hindering 

 development in a small usually circular area under the bubble. The bubble is usually 

 dislodged in the fixer, and hence a small round clear area or white spot is formed. 



Spots from, Hypo Dust and Drops. — If a film is touched by splashes of hypo or by 

 small particles of dry hypo clinging to the emulsion, local fixation can occur before 

 development, with resultant clear areas. When the trouble is from a splash of 

 hypo solution, the drop shape is often outlined by the fixed area. The area affected 

 by this means may be large or small. Hypo dust settling on the emulsion surface may 

 remain there to cause local fixation in its neighborhood. The cure is, of course, to 

 prevent hypo reaching the emulsion surfaces. Some of the common practices leading 

 to this sort of trouble include: 



1. Carelessness in handling emulsions wet with fixer. 



2. Carelessness in cleanliness of hands after contact with fixer. 



3. Permitting drops of hypo to dry on tables or tank edges with subsequent 

 possible transmission to the emulsion surface by direct contact or by draughts of air. 



4. Permitting powder remaining from handling hypo at time of mixing fixer to 

 reach the film. 



