PRINTING PROCESSES 



441 



Nowadays the photographer controls print contrast by the use of a particular 

 contrast grade of paper. Figure 12 shows the characteristics of a modern printing 

 paper (Velour Black), indicating that print character will be the same for varying 

 degrees of development time. Thus a longer development (short of fog) will produce 

 the same gamma as a shorter or normal development time. Such parallelism of the 

 characteristics for varying development time indicates a desirable quality. The 

 photographer has a certain latitude in making exposures. 



2.0 



1.6 



■« 1.0 



0.8 



0.6 



0.4 



0.2 



0.8770 1.239 1.754 2.477 3.508 4.966 6.998 9.908 14.03 19.82 28.05 39.63 56.10 79.25 



Meter Coindle Seconds 



Fig. 12. — Effect of varying development time of a modern projection paper. Note 

 that the contrast of the final print is the same whether developed for 1 J-2 or4j'^ min. Thus 

 the photographer has a certain latitude in exposing the paper. 



Tone Control. — By varying the development technique of chlorobromide papers, 

 considerable variation in tone may be effected. Silver particles, when small, exhibit 

 color. The first particles developed are these small colored particles; longer develop- 

 ment produces larger and blacker grains. The final color depends upon the proportion 

 of the colored grains to the larger black grains. This proportion is controlled by the 

 amount of potassium bromide used in the developer and by the time the print is left 

 in the developer. 



