Develop for the highlights

If the photograph is correctly exposed, to record detail in the shadows, we know that with correct development those details will be on the film. 

If that was all there was to obtaining a good negative we would be laughing all the way to the darkroom! The problem we face is that the contrast of the scene may be outside the range that the film can record effectively. Although our shadows are fine, the highlights are blown right out of the water.

The films effective range, between the darkest perceptible shadow and the lightest perceptible tone, is 5 stops and a contrasty scene can easily exceed this. The shadows will be successfully recorded if we meter them and close down two stops but any highlights, more than four stops above the shadows, will be lost to pure white.

It is in development that we can compress the tremendous range of a high contrast scene into the relatively small range of our film. By using correct exposure and development we can record detail in both the shadow and the highlight areas of the photograph, extending the films range to about 7 stops. This is called contrast contraction.

It is in development that we are trying to control the density of the bright areas and the detail in the highlights

The film is made up of silver halides which, if exposed to light, will be reduced by development to opaque silver.  The shadows on the negative that were exposed to very little light will quickly develop to completion. Remember that the shadows of the photograph are the lightest area of the negative and where the least amount of silver has to be chemically processed.  

Shadow development will be complete by half way through normal development time