Color gradient filament is fun stuff to play with. It lets you make 3D prints that slowly fade from one color to another along the Z-axis. [David Gozzard] wanted to do some printing with this ...

However, they can be programmed with a variety of gradient index (GRIN) structures including diffractive and refractive lenses. The polymers self develop in respnse to light, enabling complex 3D GRIN ...