No shape teaches you more about light than the sphere. Highlight, halftone, core shadow, terminator edge, fill light. Every fundamental lighting concept shows up.
The band wrapping around the sphere adds another layer of study. Watch how it follows the surface as you rotate the sphere, and notice how a line that looks circular from straight on becomes an ellipse the moment the angle shifts.
Orbit the camera, rotate the sphere, and right-click either surface to change their colors independently. Add lights, reposition them, and study what each one does in isolation.
Once these concepts feel natural on a simple form, the
Loomis Method applies the same logic to the structure of the head.