Nanotech Diffraction Gratings Give ETH Zurich's Chocolate an Iridescent Sheen — Without Additives

Researchers have discovered a technique for making multi-colored, iridescent chocolate — and the same technique could apply to other foods, fabrics, paper, and plastic in the future.

Late last year, researchers from ETH Zurich unveiled research by food scientist Patrick Rühs, materials scientists Etienne Jeoffroy and Anita Zingg, and physicist Henning Galinski into making chocolate shimmer with a range of colors — borrowing a trick from nature and the way a chameleon can shift its own colors — applying the same concept to the surface of a block of chocolate.

While the team is working on a path to commercialisation, however, it has not shared technical details of its approach — but Alissa M. Fitzgerald has told IEEE Spectrum that the technique likely relies on the creation of a custom chocolate mould etched using e-beam lithography. When the liquid chocolate is poured into the mould, it settles in the grooves — each measuring as little as 100nm — and when it is removed scatters light in a way to produce the multi-colored shimmering without the need for chemical additives.

If Fitzgerald is right, it's a technique which has already been applied to 3D printing: Earlier this year a method of incorporating a similar iridescent holographic-style effect 3D-printed objects was demonstrated, printing directly to P-flat sheets produced by Tectonitor — which, like ETH's supposed chocolate mould, has ultra-fine lines which act as a diffraction grating when the plastic hardens.

ETH Zurich's original announcement is available on its website, but a paper on the topic has not yet been published.