Surfaces determine the look of an object, a different step from designing the object’s shape. Color, shininess, roughness and cleanliness are elements that help tell the story or character of the object. (Wouldn't Mater from Cars seem like a different truck without all that rust?) One factor in designing an object’s surface is deciding how it will reflect or scatter rays of virtual light that hit the surface—just as with surfaces we see in real life.

Photo, bottom: © Nicolaus Czarnecki