pigmented colorants: dependence on media and time - Cornell ...

materials while lit from behind. Light will bleed on the sides and through areas
of thin volume, while a material without subsurface scattering would not exhibit
such subtle detail. This effect will also soften the shadowed areas of the material
since light traverses across the shadow boundaries from reflections underneath
the material. Also, as the scattered light traverses the material, light rays pick up
coloration before exiting. In skin, light scatters in the many layers of the epidermis
and the dermis, as well as capillaries, before exiting and reaching your eye. This
way, the sudden flush of one’s face is readily noticed by others, even though the
expanding blood vessels are relatively far underneath the skin.
Figure 2.14: Light interacts with both the media and pigments in paint.
Paint also exhibits this complex translucent behavior, where light diffuses
through multiple interfaces. Figure 2.14 shows the behavior of light as it enters a
single layer of paint, where a pigment acts as a second interface for the ray. Light
first refracted by the binding media, picks up color upon reflecting off the pigment
particle and exits the surface of the paint film. The resulting color exhibits optical
34