Ordinary black paint absorbs about 85 per cent of the light that hits it. So making something look black simply means ensuring that it absorbs at least as much as this.
Now Evgenii Narimanov at Purdue University and a few colleagues have worked out that they can do much better using a substance called a hyperbolic metamaterial, which absorbs and traps most kinds of light within its structure.
These guys created a hyperbolic metamaterial by growing silver nanowires grown in a membrane of aluminium oxide to create a flat light-absorbing slab. This absorbs some 80 per cent of the light that hit it.
That’s fairly black but then they had an idea. By roughening the surface of the slab, any light that is still reflected gets absorbed in the peaks and troughs of the surface. In effect, the photons are “sucked” into the material, say the team. The result is a substance that absorbs up to 99 per cent of the light that hits it.
Since that’s significantly better than ordinary black paint, Narimanov and co say their substance is darker than black.
There are lots of potential uses for such an idea, not least of which is to improve the efficiency of solar cells.