Shading in technical illustration brings out subtle shape attributes and provides information about material properties, as shown in Figure 10 . Most illustrators use a single light source and technical illustrations rarely include shadows. In most technical illustrations, hue changes are used to indicate surface orientation rather than reflectance because shape information is valued above precise reflectance information. Adding a hue shift to the shading model allows a reduction in the dynamic range of the shading, to ensure that highlights and edge lines remain distinct. He has a case study of improving a computer graphics animation by lowering the contrast of the shading and adding black lines to indicate direction.
Illustrators combine edge lines with a specific type of shading.
Shading in technical illustration brings out subtle shape attributes and provides information about material properties. Tufte feels that this principle is so important that he devotes an entire chapter to it in his book Visual Explanations . Based on observing several illustrations, surfaces with little or no curvature are generally flat or Phong-shaded in technical illustrations.