They created a material that excluded light with a wavelength of one millimetre (the long end of the infra-red spectrum), using an array of aluminium-oxide posts that were spaced evenly across a grid.

ECONOMIST: New-age crystals

"Typically the concentrations are small in red mud and what is present is tightly bound to the particles of iron oxide, " he says.

BBC: How toxic is Hungary's red sludge?