Development | 
FacTorIAL DEVELOPMENT (Watkins).—There is practi- 
cally a fixed relation between the time of appearance of the 
image and the total time of development to obtain a given 
density, degree of contrast, or gamma of a negative, which 
holds good for all variations of strength, amount of alkali, 
bromide, or temperature, within reasonable limits. This 1s 
known as the factorial or time development method. The 
total time of development divided by the “time of appearance” 
of the first signs of the image, exclusive of the sky in lands- 
scape work, or a white collar in a portrait, gives what is 
known as the “factor” of the developer. The following table 
gives the factors for various developers for a normal neg- 
ative : 
Adurol 5 Kodak portrait 18 
Amidol 10 Metol 30 
Azol 30 Metol-hydrochinon 14 
Certinal 30 Ortol 10 
Diogen 12 Paramidophenol 16 
Edinol 20 Pyrocatechin 10 
Eikonogen 9 Pyro-metol , 
Glycin-potash 12 Metoquinone 30 
Glycin-soda 8 Rodinal 30 
Hydrochinon with bromide 5 Synthol 30 
Imogen-sulphite 6 
The following are the factors for pyro-soda or pyro- 
potash: 
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