360 HANDBOOK OF PHOTOGRAPHY 



is based upon the results with these standard exposures. In these large laboratories 

 the customary procedure with developers for positive film is to maintain the developing 

 bath at an essentially uniform level of activity by the use of buck-up or replacement 

 solution as needed. The main bulk of developer is rarely changed. As temperatures 

 are held uniform, there are two ways of varying development, variation of time and 

 change of the rate of addition of make-up solution and overflow of spent 

 developer. 



With baths for processing the original negatives, the situation is somewhat differ- 

 ent, as the developers are much less active and are more readily exhausted. The same 

 basic methods, sensitometric tests and standard pictures may be used, but the bathf^ 

 are changed much more frequently. In general the footage of negative is much lower 

 than that of positive, so the developing systems are not so large, and this procedure 

 is more practical than it would be with positive film. 



Such methods are applied much less frequently when photographic materials are 

 processed in smaller quantities. The equipment to produce adequately standardized 

 exposures tends to be rather expensive, and the methods previously outlined usually 

 are relativelj^ more attractive. On the other hand sensitometric study of develop- 

 ment is almost necessary in the study of developing agents and formulas and in many 

 of the scientific applications of photography, regardless of quantity of material 

 handled. 



Control Methods Chosen in Special Fields. — It will be of some value to consider 

 the control methods chosen in some of the broad fields of photography, with some of 

 the reasons for the specific choice. 



Prints and Enlargements. — Prints and enlargements are typically developed on 

 an inspection basis. The amount of inspecting done will depend somewhat upon the 

 quantity and quality of work being done, being rather little in the cheaper amateur- 

 finishing stations and much more in the careful printing done for exhibit work. Often, 

 gross errors in printing exposure may be detected, when they occur, by watching the 

 time of appearance of the image, as any large deviation from the normal will show at 

 once an exposure error greater than tolerable for the quality of work being done. 



Roll Films. — With multiple-exposure units, such as roll films, no development 

 control of individual exposures has proved practical. Accordingly, either develop- 

 ment based upon inspection of the entire roll, to try to get the best for the entire 

 group, or time-temperature methods are most applicable. In many of the aids devised 

 for handling the 35-mm. film used in miniature cameras, no provision is made for 

 inspection, and hence time-temperature methods or, in the extreme case, trial expo- 

 sures are practically forced upon the users. 



Cut Films and Plates. — Cut films and plates are primarily single-exposure units 

 and hence may be treated individually if necessary. Accordingly practices vary 

 widely from place to place. Inspection methods are frequentlj^ used where suitable 

 illumination is provided. The United States manufacturers of such products normally 

 give their development recommendations in terms of formula and time-temperature 

 processing, as that is about the only language by which to transfer development 

 information from one place to another without sensitometric controls. Accordingly, 

 many places handle their development on this basis. Sensitometric control of this 

 work is rare. 



Radiographs. — To the roentgenologist the photographic side of the process is only a 

 tool to be used to his final ends. He is not interested primarily in the photographic 

 side of the process, but needs uniform results from day to day. The darkrooms avail- 

 able are often lacking in space and conveniences necessary to an independent control 

 of development uniformity. Hence, time-temperature methods and developer- 

 exhaustion compensation charts find a wide use. Carefully carried out, these methods 



