[The Action Lab] had a very serious technical problem. His daughter wanted to 3D print sparkly unicorns. But how do you make a 3D print sparkly? Turns out, he had used a diffraction grating before to make rainbow-enhanced chocolate.
The method turns out to be surprisingly simple. Using a diffraction grating as a print bed, puts the pattern on the bottom of the 3D print and — thanks to how a diffraction grating works — the 3D print now works like a grating, too.
Of course, the science behind the diffraction grating is well-understood, but we never thought of imprinting it on a 3D print. The downside, of course, is you only get one diffracted surface, but the effect is still pretty awesome.
The real test, of course, was the daughter test. Judging from the video, she was pretty happy with the results. The white pieces seem to look best, but the technique also worked with colored PLA. Technically, these are called surface relief gratings, to differentiate them from other kinds of diffraction gratings. In the 1600s, people noticed the effect in bird feathers and a hundred or so years later, they were duplicating the effect with fine hairs. It would be the 1800s before science started to explain what was really going on.