TECHNIQUE OF DEVELOPMENT 365 



ords, developers are used which are much more active than the borax developers 

 just listed. This activity is secured by greater concentration and higher alkalinitj'. 

 The latter is probably the more important of the two factors. 



Many considerations enter in the selection and use of such a formula. They 

 include: 



1. Ability to give desired gamma in an economically short time. 



2. Freedom from fog and veiling tendency. 



3. Suitability of formula for prolonged maintenance of constant developer activity 

 by additions of buck-up solutions. 



4. Freedom from tendency to stain. 



5. Ability to produce pleasing tone quality in the prints. 



6. Economy under conditions of use. 



These limitations are more drastic than in the case of negative developers, as the 

 bulk development in the industry is the development of the positive prints, and 

 economy and uniformity of work are very necessary characteristics of the processing 

 procedures. 



In this case, as in other cases, greater activity, when desired, is secured by increase 

 in alkalinity or in concentration or by decrease in bromide content. This last pro- 

 cedure is not completely independent from a control point of view, since bromide goes 

 into the developer as a product of development, and hence developers which are used, 

 as these are of necessity, have appreciable bromide content; adding solution or buck up 

 is often mixed without bromide to keep the concentration down. 



The alkalinity of the bath changes very little with use; consequently, most of the 

 aging effects are due to the exhaustion of the reducer and accumulation of products of 

 development. 



Some silver in solution is usually found after the bath is old. This does not do 

 direct harm so long as it stays in solution, but sometimes it appears to contribute to 

 dichromic fog or stain. 



Formulas producing the highest contrast are used for title work where extreme 

 contrast is desired between the letter and the background. Economy often leads to 

 developing such films in the same solution as the picture prints, but when a difference 

 is made, it is in the direction indicated. 



From elementary theory, variable-area sound records should also be developed to 

 a maximum difference in density between exposed and unexposed areas. However, 

 the advantage to be gained is often considered insufficient to warrant separate develop- 

 ing tanks and equipment. 



Typical carbonate developers as used in this motion-picture industry are given in 

 Table III. 



Developer No. 5 is typical of the positive formulas in use in the motion-picture 

 industry. Modifications are in use in some laboratories. 



Developer No. 6 is more active than No. 5 and gives a higher contrast for the 

 same developing time. 



Replenishing solutions are usually made with the same concentration as the original 

 but with all or part of the restrainer omitted, depending upon the balance sought 

 vmder actual operating conditions. 



Portrait and Commercial Work. — Through long years of work by many widely 

 separated individuals there has grown up a wide range of favorite formulas in this 

 class of work. It will not be possible to cover all the variations in this discussion. 



Pyro-soda developers have been used for many years. They are most frequently 

 prepared by making three stock solutions, mixing and diluting them as needed for use. 

 The final developer oxidizes rapidly from contact with air and must be prepared just 

 before use for best results. Contrast characteristics of the final solution mav be 



