Cast Shadow: A cast shadow is what we generally think of as a shadow. It’s a shadow created by something blocking the light source. For example, the shadow of a tree, created by the sunlight, that falls on the ground. Or the shadow on a tabletop from an apple sitting on it. Or the shadow of a nose falling on a cheek.
A cast shadow is the darker type of shadow, because it’s created by the light source being blocked.
Form Shadow: A form shadow is the shadow on a subject on the side that is not directly facing the light source. Or what you might think of as the parts of the subject ‘in the shadow’ because they don’t have direct light on them (but also don’t have a cast shadow falling on them).
A form shadow has a softer or less defined edge to it than a cast shadow. It is lighter than a cast shadow because it’s not created directly by a blocked light source. Form shadows are subtle shadows, essential for making a subject appear three dimensional rather than flat. The changes in forms shadows requires very careful observation -- squinting at the subject often help you see them more clearly. If most of the subject is in direct light, there will be very little form shadow in it.
Think, for example, of a vase on a table, where the light source is at about two o’clock. The top edge of the vase is in the direct light and there will be a cast shadow made by the vase on the table. The parts of the vase not in direct light are in form shadow.
Shadow Painting Tips:
* Squinting at a subject helps make the areas of light and dark clearer.
* Remember, shadows are not simply ‘black’. Use darker tones of the colors in the objects, or dark complementary colours.