Chatoyance

Chatoyance is the optical effect where a wood surface appears to shift between light and dark bands as the viewing angle or light source changes, most visible on curly or quilted figured lumber. It happens because wavy or interlocked fibers reflect light differently depending on their local orientation relative to the viewer, the same underlying phenomenon (different fiber structure, same optics) that gives a cat's-eye gemstone its name.

A properly finished, well-sanded figured board shows chatoyance at its most dramatic -- it's one of the main reasons figured woods like curly maple and quilted mahogany carry a serious price premium over their plain-grained counterparts of the same species.