How to make the blackest black

Black cats. Black cauldrons. The black, black heart of a goblin, witch or ghoul. Halloween is a day for black magic. But the blackest “magic” of all occurs in labs such as NASA’s Goddard Space Flight Center, where engineers are creating a coating sometimes called Super Black or NASA Black, a carbon-based nanomaterial that absorbs 99.95 per cent or more of all light that hits it. A U.K. company, Surrey Nano-Systems, has a similar material called Vantablack that they say absorbs 99.965 per cent of light. The coating was designed to reduce light that can mess with measurements in sensitive instruments.

John Hagopian, an optical physicist who led the development of the technology at NASA Goddard, described how to make the blackest black.

1. Find a substrate, or base. Engineers had traditionally used silicon, but since that substance is very brittle, NASA has turned to more forgiving materials such as titanium.

2. Apply a superthin layer of a catalyst metal, such as iron or nickel. Nothing thicker than a couple of nanometres, please (a nanometre being one-millionth of a millimetre).

3. Put the catalyst-coated substrate in a furnace. Heat to 750 C. Most metals shouldn’t melt at that temperature, but because the catalyst material is so thin, it will turn into microscopic liquid blobs.

4. Pump some carbon-filled gas in there, such as methane. The little nano-blobs will become saturated with carbon. “Just like you can put carbon in soda to make carbonated water, you can dissolve the carbon from the gas into the liquid metal,” Hagopian explains.

5. As the liquid blobs absorb carbon, they will begin to grow into carbon-lattice tubes. “Have you ever seen those fireworks where you light a little black pellet, and a little snake comes out and grows out of there?” says Hagopian. “It’s kind of like that.”

6. You should have a forest of carbon nanotubes at this point, each tube 10,000 times thinner than a strand of human hair. Crucially, this material will be very low-density: 99per-cent empty space. That way, when light hits the material, there’s almost nothing to reflect off. The photons that make up light enter and become trapped in the nanotube forest, bouncing around until they dissipate as heat. “If you want to say something scary, you can say the light photons go in but they don’t come out,” says Hagopian.

7. NASA has sent this material to the International Space Station for testing. The only instrument it is currently flying on is a laser fluorescence experiment to measure how air mixes in the atmosphere, but it will eventually be deployed in many others, including ones that can help differentiate coronal mass ejections — bursts of solar material — from the much brighter surface of the sun.