I See a Red Door

The competition to create the darkest black substance possible is not merely an exercise in marketing to fans of The Cure. A black or very dark surface looks that way because it reflects the least amount of light possible. Surfaces which absorb high percentages of light are more sensitive to light, and that means they can see and distinguish otherwise very faint light sources.

Telescopes love that.

So NASA is a place that is always very interested in advancements in light absorption. Some of the latest, according to this Physics World item by Jon Cartwright, involve the use of "carbon nanotubes," or carbon molecules arranged in a cylinder. The diameter of the cylinders can be as small as a fraction of a nanometer -- and for comparison, a sheet of paper is about 100,000 nanometers thick. The "forest" of collected nanotubes reflected almost none of the light that struck it, absorbing 99.5 percent of all the light rays that reached its surface.

Fine-tuning the density of the nanotube forest can increase light absorption. A group at the Rensselaer Polytechnic Institute produced a coating that absorbed 99.955 percent of light rays, and the substance "vantablack," noted in an entry in this space here, absorbs 99.965 percent of all light that reaches it.

The problem with many of the nanotube coatings, of course, is that they can't survive temperature and pressure extremes that may be associated with space telescopes or solar panels or other potential uses. In other words, while it's a black that looks great on the shelf, it's not one you could wear anywhere.