Instead of jumping straight to halftones and details, you can make your drawings look 3D much faster by first mapping the separation of light and shadow. This process is called shadow mapping, and it's a crucial step for establishing three-dimensional form.

Shadow mapping happens after you've established your initial proportions and major shapes. It's all about defining the edges of your shadows before you start rendering.

Key Shadow Edges

As you map your shadows, you need to identify three types of edges. The quality of these edges—whether they are sharp, firm, or soft—tells the viewer a lot about the form.

• Core Shadows: This edge runs along the terminator, which is the border between the light and shadow side of an object. The softness or hardness of this edge describes how quickly the form is turning away from the light.
• Cast Shadows: These are created when one object blocks light from hitting another. Cast shadows typically have sharp edges and help establish the relationship between different forms.
• The Silhouette: This is the outer contour of your subject. It's usually a sharp edge, but can become a lost edge if the shadow side of the object blends into a dark background.

Finding the Terminator

The terminator is the most important line to find. It's the exact border where the form turns away from the light source. Getting good at identifying this border is key to separating your light and shadow families.

On a simple form like a cylinder, you can imagine the light source's position. If the light is above and to the right, the terminator will be a line on the cylinder where the surface begins to face away from that light. As you move the light source closer to the viewer's angle, the light side of the form gets bigger. As you move the light behind the form, the shadow side gets bigger.

Applying to Complex Forms

This same principle applies to complex, organic forms like an arm. Think of an arm as a complex cylinder with hills and valleys. The terminator will not be a straight line; it will curve and change as it moves along the different muscles and bones.

Imagine slicing through the arm at any point. The shape of that slice determines the path of the terminator at that specific location.

Finding the terminator from imagination requires you to visualize the 3D form in relation to the light source. The good news is that its position doesn't have to be perfectly precise. It's more important for the shadow shape to have a good design and clearly communicate the form. You can even slightly alter the shadow shapes you see to better describe the underlying anatomy.

Common Mistakes to Avoid

When you're starting out, a few things can be confusing. Watch out for these common mistakes:

• Flat or soft light: Sometimes the light is so diffused that it's hard to see a clear terminator. In these cases, you must use your knowledge of form to invent a terminator that makes sense.
• Dark halftones: Don't confuse dark values in the light family (halftones) with the true shadow.
• Reflected light: Bright reflected light can look like it's part of the light family, but it's not. It is always part of the shadow.
• Subtle cast shadows: Be on the lookout for small cast shadows, like one muscle casting a shadow onto an adjacent one. Missing these can make the form look strange.