The Whitest White

We learned the Blackest Black has some incredible applications, beyond turning objects into mind-melting black holes. A substance that can absorb nearly all the light that hits it can work marvels on telescopes or solar cells.

The secret to carbon nanotubes – the structures that make the serious blacks possible – is to bounce photons around until they become heat. This betrays another attribute of black objects: they get hot. Most people know wearing black shirts on the hottest days is a mistake. Blacktop, tar, and asphalt are notorious for becoming much hotter than the ambient temperature, which can be a big problem for entities that can’t wear shoes.

Blacktop can get very hot

On the other end of the spectrum, white objects reflect light. As you might surmise, when bombarded with light, white objects tend to remain cooler than black objects.

Humans have long employed white paint to keep things chilly in their abodes. Lighter colors do, indeed, produce colder temperatures than darker pigments. However, most commercial alabaster paints only reflect 80 to 90 percent of the sun’s rays. While this figure is impressive, it’s insufficient to keep a building cooler than the ambient temperature. In the summer, especially, traditional white is not a solution to heat.

Aside: was the world’s most famous ivory mansion colored to keep it cool? One common myth about the White House revolves around the War of 1812, during which the British torched the Executive’s cottage. White was sufficient, the story goes, to fix the scorch marks on the walls. The only problem with this tale is the hue of the house predated the war. In fact, the whiteness arrives ironically, at least concerning today’s topic. The color originally came from a whitewash made of quicklime. The coating kept water out of the building’s porous sandstone, attempting to keep the stone from freezing and cracking. So, the white was meant to keep it warm! Eventually, lead-based white paint took over.

The White House - photo by PHC C.M. Fitzpatrick

While white is relatively cool, it’s not efficient enough to ditch air conditioning.

Perhaps motivated by Vantablack, scientists at Purdue University decided it was time to upgrade white paint. Most whites employ titanium dioxide, which does a wonderful job of reflecting visible and near-infrared light, but its fatal flaw is ultraviolet. The sun is an ultraviolet beast, which is why white paint has such a tough time staying cooler than the atmosphere.

So, the researchers at Purdue experimented with more than 100 white minerals and pigments in hopes of finding one that would outperform titanium dioxide. A clear champion emerged: barium sulfate. This compound was already utilized in a slew of applications, including photo papers, x-rays, and maquillage. Barium sulfate is as good as titanium dioxide at reflecting visible light, but it also slays ultraviolet rays.

The team at Purdue had stumbled upon the Whitest White in the world!

Professor Xiulin Ruan displays the planet's whitest white paint - Purdue University

This breakthrough admittedly looks a lot less impressive in photographs than Vantablack, but its implications might dwarf the jet coatings.

The Purdue paint reflects 98.1 percent of light! This figure is above the magical threshold for temperature. The whitest white grants a surface the ability to remain cooler than the surrounding atmosphere.

Professor Xiulin Ruan told Smithsonian Magazine, “Our paint can lose heat by its own emission—it emits heat to deep space. With such little absorption from the sun, our paint loses more heat than it absorbs. This is really exciting for us. Under the sun, it cools below the ambient temperature and that’s hard to achieve.”

Their concoction kept buildings 8 degrees cooler than the ambient temperature during the day and an astounding 19 degrees cooler during the night. This power, simply from slathering something with some paint, could have huge ramifications across the globe.

The purple section on the right shows the new paint photographed by an infrared camera, displaying its cooler-than-ambient temperature - photo from Purdue University

As the planet continues to warm, any advancement that might mitigate energy usage could have a dramatic effect. Testing showed the Purdue invention provided 113 watts of cooling juice per square meter. On a 1,000-square-foot home, that’s about 10 kilowatts, which is more than the typical air conditioning unit requires. In other words, this paint might render air conditioning unnecessary, or, at least, reduce its need. Spread the paint across the world and the energy saving would be massive.

Of course, the paint could go on things other than buildings, meaning its reach could be even more massive.

However, as inquiries flooded Purdue hoping to use the paint on automobiles, airplanes, or spacecraft, they realized an issue. The barium sulfate paint was fairly thick at 400 microns. On top of a roof, this thickness was irrelevant. On an airplane, the amount of paint on the craft directly impacts its efficiency; the breadth of the new paint was not worth the radiation it saved.

No matter, the Purdue team got to work and whipped up a better version.

Old width vs. new width - Purdue University

They shaved the stable formula down to 115 microns.

Soon, nearly every vehicle that doesn’t color for vanity might hit your eyes with the whitest white created to date. Some people think red or blue cars are cool, but those hues have nothing on the hipness of white.

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