TECHNIQUE OF DEVELOPMENT 363 



These effects are most noticeable under conditions such that there is a large density 

 difference between one area and its neighbor. They are less and less noticeable 

 as the density difference diminishes and as the developer agitation is increased. The 

 agitation evens out the development and makes it less subject to these local effects. 



Irregularities of Agitation.- — -Uneven and irregular agitation can be produced in 

 many ways. When the developer is nearly stagnant, small temperature differences 

 may set up thermal currents sufficiently great to produce streaks. 



As the agitation increases, disturbance due to this cause is less important, but 

 regular hues of rapid and slow flow may be set up with resulting uneven development 

 agitation. Holes in films and film hangers are a frequent contributing cause of streaks 

 due to systematic differences in agitation. Such holes may produce local turbulence 

 and agitation increasing development locally. An extreme case of this occurred when 

 some motion-picture film was being developed in a "Stineman tank." This tank held 

 the film in a spiral, wound on a form in a horizontal plane. The developer tray was 

 set in a water bath for temperature control, and this bath was agitated by a stream of 

 compressed air to insure uniformity of its own temperature. The resultant vibration 

 of the developer in the tray was enough to cause streaks from each sprocket hole. 

 These disappeared when the water bath was left completely stagnant during develop- 

 ment or when sufficient agitation was introduced by rotating the reel holding the film 

 to smooth out the uneveness due to the sprocket holes. Similarly, streaks on cut 

 films, developed in one of the common styles of developing hanger, can sometimes be 

 traced to the holes put in to lighten the frame and permit drainage of the solutions. 



Reticulation. — At times under unfavorable conditions of processing, the gelatin, 

 when it finally dries, is no longer smooth and even but is rough and presents an 

 orange-peel type of surface and, in the more extreme cases, a cracked appearance. 

 This condition is known as reticulation. It is usually caused by (1) solutions used 

 at too high a temperature, (2) too sudden changes in temperature going from solution 

 to solution, (3) too great changes of pH in going from solution to solution with con- 

 sequent rapid change in swelling of gelatin, or (4) unsuitably warm and humid drying 

 conditions. Care in selecting the working conditions and formulas to avoid the 

 hazards noted and to secure favorable conditions should result in avoidance of this 

 difficulty. 



Formulas. — The choice of a suitable developing formula is an essential part of 

 successful photographic work. Many different formulas may be found in the litera- 

 ture recommended for very similar uses, with few comprehensive comparative tests 

 by which to judge their relative value. In the commercial field, when large bulks of 

 chemicals are to be handled, it is often necessary to consider the initial cost and useful 

 life more critically than necessary where the quantities in use are small. All these 

 factors make the evaluation and complete comparison of all possible formulas much 

 too broad and complex for fully detailed discussion. Accordingly, as a compromise 

 between uncritical listing of all formulas suggested and too broad generalizations, the 

 data are presented in the form of a limited number of typical formulas and tables 

 indicating the range of concentrations of the various developer ingredients representa- 

 tive of developers of the specific type under discussion. Of necessity there has been 

 a certain amount of arbitrariness in the selection of the individual formula listed as 

 typical. This should not be construed as meaning that other formula are not good, 

 but a complete presentation is, of course, impossible. 



Developers for the Motion-picture Industry. Borax Negative Developers. — Borax 

 developers are used quite generally in the motion-picture industry for development of 

 picture negatives and variable-density sound-track negatives. The formula chosen 

 depends upon the emulsion type, the contrast desired, the degree of agitation used, 

 and the developing time considered desirable. The more concentrated and active 



