The Blackest Black

Black is often described as the absence of light. For instance, an object of any color, even the brightest of whites, appears black when you remove all light sources. But in reality, the objects retain their own specific colors; you just can't see them because there is no light reflecting off them to your eyes. With a light source reflecting off a colored object, your eyes interpret the reflected light. But what about the "color" black? Black is not really a color, for it is not in the visual light spectrum (think of a rainbow), nor in the traditional "color wheel." It can be considered, in fact, to be the state of no color at all. However, when light is shone onto a black surface, we "see" black, don't we?

We can see black because the black surface is reflecting some light back to our eyes. The amount being reflected is much less than white or any of the other colors, but it is still measurable. For instance, conventional black paint reflects 5-10% of light. That is to say, it absorbs 90-95% of light. This absorption of light is the reason dark surfaces are always much hotter in the sun than light surfaces. The National Institute of Standards and Technology has set the standard of "black" as that which absorbs 98.6% of light. This standard black is the object on the far left of the photo above. The object on the far right is a piece of glassy carbon.

And the object in the middle? In 2008, Shawn-Yu Lin of Rensselaer Polytechnic Institute (Troy, NY) led a team that created a black that is 30 times darker than the NIST standard. The paper-thin material absorbs 99.955% of all light that hits it, making it the darkest substance ever created.

It is made of carbon nanotubes -- microscopic, hollow fibers whose walls are just one atom thick. The fibers are spaced wide apart, creating enough space to allow light in and almost no surface area for the light to bounce back out. Unlike most surfaces, this material absorbs light evenly and equally from all angles.

So, is this just a fun fact, or are there practical applications for this? This technology can revolutionize solar energy panels, because they will be able to absorb all sunlight that strikes the surface, and the panels will not have to be moved to follow the sun to ensure the optimum angles. This can also be used to render objects nearly invisible -- they cannot be seen because there is no reflected light that will reveal their presence. This means it will be an effective countermeasure to night-time vision technology, because even ultraviolet and infrared light will be fully absorbed.

Coated objects will not be invisible in the sense that you can see right through them, but there are theories that this level of light absorption will make it possible to bend light around the object to reveal objects directly behind it. Perhaps this is the prototype for a Harry Potter Invisibility Robe?

So, you want to go to Walmart and purchase some of this black stuff, perhaps to coat your car, so it will outwit those nasty stoplight cameras? Well, because the process involves the complex production of nanotubes, and you'll need a great many of them to make it worthwhile, a gallon of the material in paint-like form might cost as much as $100,000. Maybe there will be a clearance sale of the second-most blackest black?