h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

February 06, 2003

Scientists turn future blacker than ever
By Mark Henderson, Science Correspondent



BRITISH scientists have developed the darkest colour ever produced, up to 25 times blacker than conventional black paint.
The super-black coating, invented at the National Physical Laboratory (NPL) in Teddington, West London, absorbs almost 99.7 per cent of the light that strikes it, making it the darkest and least reflective surface on Earth.

The darkest industrial coatings available at present absorb only up to 99.4 per cent of light, while the best matt black paints absorb no more than 97.5 per cent. The printer’s ink on this page absorbs 95 to 96 per cent. At certain angles, the new colour, known as NPL Super Black, is blacker still, reflecting 25 times less light than everyday rivals.

The development promises to revolutionise the design of optical instruments such as telescopes, spectroscopes and radiometers, which use black surfaces to minimise the scattering of stray light.

The coating, which is made of an alloy of nickel and phosphorus, is extremely stable, even under the very low temperatures of outer space, and the scientists behind it believe it could be used to improve the accuracy of orbiting instruments such as the Hubble Space Telescope. The Highways Agency has also inquired about using it as a backing for road signs.

It cannot, however, be made into a paint or ink because it is created by a complex two-stage process that coats metal or ceramic plates in the colour.

The object to be blackened is immersed for five hours in a solution of nickel sulphate and sodium hypophosphite, leaving a nickel and phosphorus coating. This is dipped into nitric acid, which etches on the ultra-black surface, according to New Scientist magazine.

Richard Brown, a senior research scientist at NPL who led the development team, said: “NPL Super Black will be available to a wide range of users across many areas of science and technology, and its benefits are enormous. One of the advantages of this new black is that it can withstand cryogenic temperatures without cracking.”

An early application is likely to be in the construction of star trackers, the devices with which space probes navigate with reference to the position of the stars. The instrument generally consists of a black painted tube up to 50cm long, which absorbs stray light and allows the stars to be monitored. An NPL Super Black coating would allow the tube to be up to a third shorter, making the probe lighter and cheaper to launch.

Several artists are also keen to use it. “When you look at the black, it is an incredibly beautiful surface,” Nigel Fox, head of optics at NPL, said. “It’s like black velvet.”