Separating form edges from cast-shadow edges

Identify whether a dark shape comes from a form turning away from light or from another object blocking the light.

What it is

A form edge appears where a surface turns away from the light. It belongs to the object’s own shape, such as a cheek, cylinder, or sphere, and often transitions gradually as the surface curves.

A cast-shadow edge appears when one object blocks light from reaching another surface. The shadow’s shape comes from the blocking object, called the occluder, but the shadow lies on a different surface.

For each dark shape, identify its cause. Let form edges follow the surface curvature and usually remain softer. Shape cast shadows like the occluder, with sharper edges near contact that soften as the shadow moves away.

Why it matters

Separating these edges helps volumes read as solid and helps objects sit on the surfaces beneath them. Confusing them can make form turns look outlined, cause cast shadows to merge into the form, and make faces look dirty or objects appear to float.

You can check it when

✓Label each dark shape in your painting as a form turn or a cast shadow.
✓Check that cast shadows follow the casting object’s silhouette and wrap across the surfaces where they land.
✓Check that form edges follow 3D curvature and are generally softer, while contact and cast-shadow edges are more defined where objects touch.
✓In a photo study, trace form-shadow regions and cast-shadow regions separately, then compare that separation in your painted study.

Separating form edges from cast-shadow edges

What it is

Why it matters

You can check it when

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