Whitest paint is now thin enough to coat cars and planes | Hacker News Reader

Whitest paint is now thin enough to coat cars and planes

newatlas.com

56 pointsbilsbie69 comments

Open articleView on HN

If you mixed it with Vantablack, would you get the greyest possible paint? /s

You could try buying some and find out!

https://culturehustle.com/products/black-v1-0-beta-the-world...

You could also mix it with the 'whitest white'

https://culturehustle.com/products/white-20

You linked to black 2.0. It may very well be the blackest black, but it is decidedly not Vantablack. I think this is worth distinguishing, because interestingly, I don't think just anyone can get their hands on Vantablack because someone obtained exclusive rights to it. :) https://en.wikipedia.org/wiki/Stuart_Semple#Conflict_with_An...

Many years ago I bought some of the black 2.0 on a lark, and honestly both brush and air brushing seemed to produce very meh results. Like nothing that to me indicated any significant difference in matteness vs many other paints I’ve used. Now I realize I didn’t try applying it to actual glass or anything, but even on polished resin it didn’t stand out as meaningfully different.

Vanta black is a whole different beast, but it also isn’t paint so I feel it’s cheating that particular race :)

In my experience black 2.0 is pretty dang black, but it's not nearly as black as the marketing photos make it seem. It's still plainly visible in daylight. It's a structural black too, so in general touching it will make it more gray.

Still an amazing product for all sorts of art, but also for building telescopes or photography hardware.

Fair enough! I hadn’t thought of it in terms of things like telescopes, so good to know.

You can't mix Vantablack. It actually isn't paint, it is a coating grown through vapour deposition.

How does this new paint compare to the contents of a spray paint can from Home Depot?

Having a hard time searching the web for this one, the first few pages of hits are all about this new 98.1% paint.

You’re looking for something called “light reflectance value” or LRV.

You can get 90-94% in wall paints; not sure about spray paints.

https://www.kylieminteriors.ca/paint-colour-review-the-5-whi...

Thanks both, great q/a

Re >> "with an ability to reflect around 98% of incoming sunlight"

Seems like a mirror would reflect even more light. Now, obviously we don't want to make the exteriors of our buildings and cars a mirror!. but it made me wonder: What's the difference between a really really really white paint that reflects 98%+ light, vs. a reflective surface? Is it that the white paint reflects the light, but in a "scrambled" form, thus losing the image?

Nope.

Silver reflectivity is about 95%, aluminum reflectivity is about 90%.

So the best metallic mirrors are worse than the best white paints, even if they can be better than the frequently used white paints based on titanium white (89.5% reflectivity).

Total internal reflection might be closer to 100%, but that cannot be used for the light that comes from the air on the surface of a mirror.

A simple way to verify this is to observe that common mirrors also tend to be green, showing that the other colors are absorbed more by the mirror. If you face two mirrors towards each other you will see a lot of green.

edit: here's an example: https://i.imgur.com/Ar80FYZ.jpeg

The common mirrors have the metal on the back side, so their reflectivity is diminished by the absorption in the glass.

The better mirrors, which are used e.g. in telescopes and some other optical instruments, have the metal on the front side, but that limits the metal choice to aluminum, because silver is tarnished quickly by the sulfur compounds present in the air.

so why don't common mirrors just use aluminum? It's already cheaper than silver, right?

The common mirrors have been using aluminum for a long time.

I do not know when aluminum has replaced silver, but it was probably not a long time after WW2.

The silver mirrors had the advantage that the metal could be easily deposited from a water solution, anyone could make silver mirrors at home, if desired.

The aluminum mirrors use a vacuum deposition process, which requires very expensive equipment, but the cost per mirror is much less.

Ah. I misunderstood your earlier comment. Thanks!

You can have dielectric coatings on a mirror that increase the reflectivity to >99.9% (and over a wide range of wavelengths). You can of course get a lot more 9's if you only care about a narrow band.

https://materion.com/products/precision-optics/application-f...

https://en.wikipedia.org/wiki/Dielectric_mirror

99.9% for visible light does not mean 99.9% for all the solar light.

Most dielectric coatings absorb ultraviolet light so they reflect much less of the total solar light, most likely less than 90%.

Such a mirror with dielectric coatings would not be able to cool the object on which it is applied, unlike the paints which are discussed in the article, which are based on boron nitride, barium sulfate, calcium carbonate or fluorinated polymers, all of which do not absorb ultraviolet light.

The common white paints based on titanium white or zinc white also absorb ultraviolet light, so they cannot be used for cooling an object illuminated by the Sun.

What I’ve seen says silver and aluminium are both a bit better than that.

https://www.researchgate.net/figure/Reflectance-versus-wavel...

https://www.researchgate.net/figure/Reflectance-of-Ag-Au-and...

I think this better fits my observation that a clean mirror can easily be unnoticed in an environment similar in all directions, such as woodland or a messy room.

What counts is not the peak reflectivity from those graphs, but the integrals over the solar spectrum.

Aluminum has lower reflectivity everywhere, but it retains a high reflectivity in ultraviolet.

Silver absorbs ultraviolet, which lowers the integrated reflectivity over the complete spectrum.

A few percent difference in the total reflectivity can make a large difference in the cooling power of a paint, but a few percent difference in the reflectivity of a mirror is unlikely to be perceived visually.

Fair, I was only thinking of the visual spectrum and in this context that’s not right. :)

I love HN for answers like this

To make things simple, yes, that's is. White "scrambles" the light, the correct term is "diffuses" but that's the idea.

Maybe quantum physicists will disagree but the difference between a mirror and a white surface is that a mirror is perfectly flat and therefore will reflect light at always the same angle. It may absorb some of it, or even most of it (black mirror!) but what it reflects, it will do it always the same way.

A white painted surface can be thought as a surface covered in tiny mirrors, all pointed in a different direction, and depending on which tiny mirror a ray of light will hit, it will be reflected in a different direction. With large pieces, like with a broken mirror, you will still see (as you said) scrambled images. But because the pieces are so tiny, you won't be able to make out an image and you will only see white. A glass pane can look like a mirror, but reduce it to a powder and it becomes white. It has nothing to do with absorption, you can have a 1% reflective mirror, and 100% reflective diffuse white.

The way the "tiny mirrors" that make up the white paint are oriented give out its general look. Have them oriented mostly with the surface and you get a glossy finish, have them randomly oriented in many directions and you get a matte finish (this is called specular reflection btw).

I've seen mirrors be called "smart white", it is white because it reflects most light in most wavelengths, and it is smart because it keeps the rays of light oriented.

yes. A white surface scatters the photons and a reflective one keeps them in the same position relative to the others. If you make a surface smooth enough it starts becoming partly reflective. There is also scattering of photons that happens in object itself

I found this video about the topic to be interesting: https://www.youtube.com/watch?v=1n_otIs6z6E (title: Why aren't Mirrors White? Why isn't EVERYTHING a Mirror?)

Yes, it's not reflecting the light so much as re-radiating it in a diffuse pattern.

I don’t think there’s a physical difference between reflection and re-radiation, is there? Reflection is just highly organized/non-diffuse.

reflection is coherent, a single physical process. The light keeps it's phase and polarization. Re-radiation is incoherent, caused by multiple particle interactions (physical processes). So there's quite a difference in physics.

Can you explain? As I understand it, in both cases, a photon comes in, gets absorbed by the material, and then gets re emitted.

It's things like this that have the potential to have big effects. Savings to cooling will directly improve energy efficiency and thus CO2 production.

I know white clothing often contains "brighteners" which fluoresce, converting received UV light into visible wavelengths, so the resulting white is brighter than what is reflected in the visible spectrum.

I'm just curious what role that ever plays in paint, if this 98% reflectivity is a big deal, or if we already have white paint with over 100% because of brighteners.

This 98% reflectivity refers to the total solar light, including infrared and ultraviolet light, because the purpose is to cool whatever is painted, despite being illuminated by the Sun.

With fluorescent paints, the energy of the emitted visible light is always less than the energy of the absorbed ultraviolet light. The difference is heat that warms the paint.

The paints discussed in the article also reflect the ultraviolet light. Moreover, they also emit infrared light in the frequency band where the air is transparent, and that infrared light leaves the Earth if the painted object is outdoors, which will be true for a building or for a car while it is used. By emitting more energy than it is absorbed from the solar light, the painted object is cooled (if it is outdoors).

While I find it very interesting that boron nitride can outperform all other white pigments in the combination between total solar reflectance and layer thickness, I believe that an another approach for making a white paint is even more promising.

That method is described in the reference #17 from the bibliography of this paper.

There are 2 methods that can be used to make a white paint.

The first is to use a polymer as a binder and incorporate in it very small particles with high refractive index, i.e. a white pigment powder.

The second method is to make a polymer that solidifies as a foam. In this case, the polymer contains voids filled with air having low refractive index, instead of pigment particles, but the effect of the optical non-homogeneity is the same, so both foams and powders are white, when they do not absorb light.

The reference #17 describes such a method of making a polymeric foam, which can be used as a paint.

According to the table from this paper about boron nitride, the previous best combination of total solar reflectance and layer thickness and layer density was for that polymeric foam, which had a 96% total solar reflectance and a 300 micron thickness, outperforming all the previous paints based on white pigments.

While that foam had a slightly lower total solar reflectance, it had a better far infrared emittance, so the cooling performance was similar, i.e. of about 6 Celsius degrees below the air temperature.

Because the methods that use foams do not need pigments, they have the potential to be cheaper than the methods with pigments, which need both a polymer as binder and a mineral pigment.

Moreover, methods to make foams can be adapted to many different kinds of polymers, so there are chances that other polymers with even better performances or even lower cost can be found, perhaps a silicone polymer in foam form (silicones can have perfect resistance to solar light in outdoor conditions).

Are airplanes more in need of cooling or heating? The outside temperature at cruising altitude is around -50° (roughly where the Celsius and Fahrenheit scales meet, btw), is the insulation good enough to just keep the inside at acceptable temperatures for humans?

The article mentions airplanes waiting on the ground, but I do wonder what happens during flight. I suppose the engines create plenty of heat after all.

It does not matter for airplanes. Both cooling and heating are in ample supply on an airplane.

Cooling is in short supply when the aeroplane is parked on the ground. In some climates external air conditioning units are required to maintain a manageable cabin temperature.

Hence why the majority of airline fleets have white-painted upper fuselages.

If this takes over and is used everywhere, in 50 years, will people become nostalgic over titanium dioxide white? Will the titanium industry be supported by the few remaining vintage white paint manufacturers? \s

I think people will in fact get nostalgic about titanium dioxide white. Actually any white. Looking at the progress, in 50 years every surface is going to be covered with ads.

I know nothing about this sort of stuff, but if this were applied to cars, would there be an increased risk of temporarily blinding other drivers on a sunny day?

It reflects something like 98% of light instead of 90%, so the actual increase in reflected light isn't that big.

Flat scattering surfaces are never blinding. The problem is with specular reflections off of shiny surfaces. Even though a shiny surface may only reflect a small fraction of incident light, it's all pointing in one direction which can dazzle observers.

For the visible effect, you are right that there is little difference between 90% and 98%.

For its intended application, reflecting 98% instead of 90% means absorbing 5 times less heat when under Sun light.

That is a very large difference. A white paint with only 90% reflectance might cause negligible cooling, while one with 98% reflectance may cool a painted object to have a temperature less by more than 6 Celsius degrees in comparison with the air temperature.

The cooling depends on the ratio between how much solar light is absorbed and how much far infrared light is emitted.

So a cooling paint must be very white over the near infrared, visible and ultraviolet spectrum, but it must be black for the far infrared light which is emitted by the bodies at ambient temperature.

It won't shine any brighter than the light that's hitting it.

Like... the sun?

Not like the sun. A white object is thousands of times less bright, because in every direction it emits an average of the light hitting it and the sun is such a small fraction of the sky.

Still, snow can cause blindness: https://en.wikipedia.org/wiki/Photokeratitis

How does it affect white balancing on traffic cameras?

Finally, we can make the city in Mirror's Edge [1] into reality!

1 https://en.wikipedia.org/wiki/Mirror%27s_Edge

> The new material features boron nitride in hexagonal nanoplatelet form and offers a solar reflectance of 97.9%

What's the difference between white paint and a mirror? Scatter?

Yep — mirrors are coherent while white paints scatter, even though they reflect similar amounts of light.

Yes, exactly.

I wonder what difference a metal roof would make temperature wise to have this stuff on it in broad daylight?

The future is now, and it is blinding!

Surfaces get dirty in the real world. Won't these fantastic figures degrade rather quickly?

Couldn’t this be revolutionary for spacecraft?

Also would it make a better solar sail?

Colour me stupid, but in a simple white vs. black comparison, wouldn't a VantaBlack-clad solar sail absorb more energy, so be more useful?

- ed I'm misunderestimating 'equal and opposite' photon reflections here, aren't I?

For solar sail you don't want to absorb, you want to reflect.

When you absorb you only get half of the push (assuming reflective surface reflecting directly back at 100% efficiency vs absorbed heat that gets radiated omnidirectionally).

If you’re harvesting the energy from photons into heat, you’d want black. Any photon hitting your sail would be absorbed, and give you its momentum and energy.

If you’re harvesting the momentum from a photon into momentum for your spaceship, you’re better off with white. A photon being reflected gives you its momentum twice. It’s first (briefly) caught like the black sail, imparting its momentum, but then it’s re emitted and hurled away, like a cannon, giving even more reactive momentum to the sail

This would be really cool for a shirt or hat.

Boron nitride and barium sulfate pigment.

Very cool, but im skeptical about cost

With less than 300 grams of paint per square meter and a pigment made from cheap ingredients, it is unlikely to be more expensive than titanium white, but obviously this will be true only if it will be produced in large enough quantities.

Yeah I mean I think all comes down to scalability not necessarily raw materials.

Reply on news.ycombinator.com