5 value system

 

1. light tone
2. half tone (in shadow)
3. form shadow (=core shadow)
4. reflected light
5. cast shadow

Cast shadows: Shadows made when the light is blocked from hitting an adjacent surface
Form shadows: Shadows made by the turning of the form, away from the light source.

The form shadow is the shadow that is on the form itself, created as the form turns or faces away from the light source. Form shadows have soft, blended edges; however, on cubes and angular objects, the form shadows have hard edges.
The second type of shadow is the cast shadow. The cast shadow is created when an object blocks the light and ccasts a shadow onto adjacent surfaces. cast shadows are darker where closer to the object, and they slightly lighten in value as they move away from the object. Cast-shadow edges are crisp, and they slightly soften as the shadow moves farther away from the object.