Nxylon: New super-black material made from wood | Hacker News Reader

Nxylon: New super-black material made from wood

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183 pointsthrowaway256273 comments

> Most surprisingly, Nxylon remains black even when coated with an alloy, such as the gold coating applied to the wood to make it electrically conductive enough to be viewed and studied using an electron microscope. This is because Nxylon’s structure inherently prevents light from escaping rather than depending on black pigments.

I don't follow this at all. If it's coated with an alloy, Nxylon isn't on the surface of the object anymore, the alloy is. So the alloy should be reflecting light. What am I missing?

A layer of very thin gold can be transparent.

I see, thanks for filling that in.

Famously seen on the Apollo space suit sun visors. Their gold layer is thick enough to look gold, but thin enough that you can see through it:

http://heroicrelics.org/apollo-wwwttm/apollo-suit-a7l-leva-v...

You can see through it at least in part because of the tint/opacity effect, where there is more light on the outside than the inside. It's why you can't see through it the other way around (it's reflective, you don't see the astronauts' eyes).

That would imply the result of overlaying Nxylon with this would be gold-colored, not ultra-black..

Right, but less reflective than solid gold, since some of the light is going _though_ instead of bouncing off

So as you make the layer even thinner than the sun protection on those Apollo visors, you have even more light going through, and even less that can bounce off

I interpreted this along the lines of it not being a pigment, rather it's black because something about it's physical structure at a small scale causes light to not reflect back. Adding a thin coating of gold would not necessarily change that structure so it would continue not reflecting light.

^ pure conjecture

I believe it's something called "structural absorption", similar to what happens on birds of paradise feathers [1]

[1] https://www.nature.com/articles/s41467-017-02088-w

I'm way out of my depth here, but I think this comparison to the birds of paradise feathers makes the most sense in terms of me visualising what Nxylon would look like with a thin metallic coating

I wonder if this pattern is considered similar to fractals? Or would that work even better? I recently learned that we have figured out how to produce fractal light from lasers as well which sounds quite interesting and useful.

Maybe the reason radio waves travel poorly through trees is due to the leaves having a fractal-like structure as well? And since light is also just electromagnetic radiation too, it makes sense that this phenomenon could also be used to absorb light itself, if I'm understanding correctly. I wonder if this is how stealth paint on aircraft works?

> Adding a thin coating of gold would not necessarily change that structure

My confusion is that I would normally expect a layer of gold not to permit any light to pass through. The underlying structure wouldn't be receiving any light, so there would be no photons to trap. Apparently a layer of gold can be applied thinly enough to transmit appreciable light, though.

Gold foil can be beaten to under 2 micrometers.

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

This part of the article confused me, because what does a black pigment do if not "inherently prevent light from escaping"? That's kind of just the definition of absorb.

This, different article, https://www.earth.com/news/new-super-black-wonder-wood-calle..., suggests the process is high-energy plasma affecting the cut ends of the basswood fibres.

That article has a paper link: https://doi.org/10.1002/adsu.202400184

"The researchers have developed prototype watches and jewelry" What kind of a research team is this, fashion? :)

Also, the black parts there really didn't look that dark.

They are also all watch designs that I get served instagram ads for, coincidentally

I recognized the right watch immediately to be this one [0]. But i guess they just replaced parts of the watchfaces with their material?

[0]: https://www.holzwerk-uhren.de/en/products/holzwerk-eifel

The one on the left appears to be this one [0].

[0]: https://magneticballwatches.com/products/simple-fashion-ball...

Those watches have crystals on them.

What’s the chemistry at play here to achieve this?

Does it burn “lighter” compounds away to leave dark ones behind? Does it cause a reaction to turn lighter compounds darker? I couldn’t see details of the mechanism. Which is important since presumably some mechanisms would give a hint that the process can be tried on other materials or types of wood.

The article mentions it works on other types of wood but doesn’t explain why, or if it works on all woods.

Well they say it doesn't rely on pigments, so I'm inclined to think it uses some sort of nano-structures, like "improved" vantablack. Like a forest where light goes in, but just get's scattered long before it can make its way back out. Ben did a really nice video about that homemade stuff, including (of course) some electron microscope images.

https://www.youtube.com/watch?v=Xr1AiExSAnU

Maybe the cut cell acts like a hemispherical shell coated in carbon. Light enters, bounces around inside a couple of times, gets absorbed?

Two things are at play, the lignin (light absorbing) is emphasized and the cellulose is burnt away (light reflecting), and it seems this combined pretty unique lattice system (they use a similar synthetic system when producing regular ultrablack paint but the natural one appears to be more complex) create the blackness.

It's probably a combination of the surface being black in colour (charcoal), plus a surface texture that absorbs light.

It brings to mind the way feathers and insects often have brightly-coloured parts that aren't due to pigment but rather the microstructure preferentially absorbing/reflecting specific wavelengths, giving a colour.

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

Similarly, I wouldn't be surprised if the microstructure is tuned to work best (lowest reflectance) in the visible light range.

EDIT: limited wavelength range also applies to other "super-black" materials https://en.wikipedia.org/wiki/Super_black#Technology

Check the paper, especially figure 5: https://doi.org/10.1002/adsu.202400184

Burning the end-grain wood makes a particularly complex porous structure that minimizes the chance of reflected light escaping ("velvety").

> Nxylon (niks-uh-lon), after Nyx

It seems the most straightforward spelling (and easier to pronounce by looking at it if you are taking any kind of cues from the rest of loan words in the language) would have been Nyxlon.

I read it as "N-xylon", where "ξύλον" is wood in Greek.

The ceiling and wall tiles mentioned at the very end of the article sound really cool.

A room where all the walls, floor, and ceiling are made of this would be pretty disorienting, wouldn't it? Even with a light source that let you see all the people in the room, wouldn't it just look like you're all in a pocket dimension?

Wow. I didn't even think of that option! I was just thinking of accent tiles.

Sounds like a great way to build black body emission sources.

Just panel the interior of a box with this stuff and put a hole in one wall.

It does depend on the spectral properties a lot. Figure 3 in https://onlinelibrary.wiley.com/doi/10.1002/adsu.202400184 seems to indicate that the behavior in the very near infrared will be pretty good. It stands to reason that this behavior could be optimized by process improvements.

This is going to result in an awesome Applied Science video... I hope!

Making this at home will be quiet interesting.

Hopefully the writers of Parks & Recreation will be aware of this research when writing the second reunion show.

https://youtu.be/pTme7k5sV-o?si=sbAYH5FAg4n4G4LS

How much more black could it be? None. None more black.

How does it compare to the other super-black materials, the Vantablacks and the like?

Probably less carcinogenic.

I dunno, it looks like they're creating carbon nanostructures; while wood carbon / soot seems fairly benign, I still wouldn't want to breathe it.

And tar/pitch is definitely carcinogenic

that's what a lot people with wood burners used to say...

Yeah, but everybody chain-smoked from age 3 in those days, so it's not easy to tell.

Here [0] is the paper in question, it has a chart that shows the reflection rate of this one at around 0.3 - 2%; the paper itself has the following quote for the competitors:

> Far lower reflectance values have been achieved with materials containing aligned carbon nanotubes (CNT), for example a low-density CNT array (0.045%),[11] the coating Vantablack (0.035%)[7] and a CNT-metal foil (0.005%).[12] The current holder of the “record” for a low reflectivity material (<0.0002%) is an ion-track micro-textured polymer with anti-backscatter matrix.[13]

So they're arguing that it's on-par with Vantablack but not the newer materials.

[0] https://onlinelibrary.wiley.com/doi/10.1002/adsu.202400184

From your numbers Vantablack is 0.035%, whereas the new process bottoms out at 0.3%. So they’re within 10x of Vantablack, but not on the same level.

If my understanding is correct, Nxylon is lighter than Vantablack (in terms of weight) but reflects slightly more light. This means that it is less effective than Vantablack at absorbing light.

Looking at the watch photographies, how is this "super-black"?

A pity they hadn't read Gene Wolf's _Book of the New Sun_ in which the main character wears robes of "the hue fuligin, which is darker than black, admirably erases all folds, bunchings and gatherings so far as the eye is concerned, showing only a featureless dark."[1] From the Latin for soot.[0]

[0] https://www.merriam-webster.com/dictionary/fuliginous

[1] http://www.technovelgy.com/ct/content.asp?Bnum=1495

https://www.youtube.com/watch?v=pAgnJDJN4VA

Does it rub off?

[flagged]

Neither of those generally results in <1% light reflectance however.

Light doesn’t normally cut through solids, doesn’t mean lasers aren’t a useful or unexpected technology.

[flagged]

+1 But I’d like to add I think the HN comment is right about 2% of the time

Don’t forget that writing nodejs code qualifies you to have an opinion on anything scientific.

"Please don't post shallow dismissals, especially of other people's work."

https://news.ycombinator.com/newsguidelines.html

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