Anatomy of a shadow

When giving dimensions to an object, we must add light to the object. 

Anatomy of a shadow to give dimensions to the form. From: https://www.artistsnetwork.com/art-mediums/drawing/3-figure-drawing-mistakes

A light source is from where the light is comming from. So, when light source is giving light to the object, then the object becames divided into two sides:

• the light side
• the dark side

The highlight is the lightest section of the light side, where the light is more intense.

The midtone shows the real color of the object and stays in the light side, between the highlight and the core shadow.

The darkest part of the object is the core shadow, which is the shadown of the object within the object itself. The core shadow divides the two sides of the object, but stays in the dark side part of the object.

The reflected light, is at the dark side of the object, at the bottom edge. This is the light that is bounced back from another object or from a surface to the object itself: it is lighter than the core but darker than anything from the light side.

The cast shadow is the object of the object in the surrounding surface. It can be added to the drawing, in the opposite direction of where the light is comming from. 

The darkest part of the drawing is right below the object, where the cast shadow begins, which is the occlusion shadow.