I had to rebuild my autocue recently,
for… reasons.
And one thing I noticed from testing the new one was that when the phone underneath switched on,
the camera would wash out. And it was obvious why:
the light from the phone went up… illuminated the white foam board above… and that reflected
down into the acrylic… and into the camera. So that really underscored the importance
of painting the inside black as I did with the old one.
And that was also an excellent excuse to get some of Stuart Semple’s Black 3, or 3.0,
whatever, and talk about the chemical physics going on with black surfaces.
What do they need to do to work really well.
If you don’t know the
story of Black 3, we need to jump back a few years to the production of something called Vantablack.
This is not a paint, it’s not a pigment… it is a carbon-based, nano material, which is literally
grown onto a surface by vapour deposition. In this process, you vaporise carbon at
high temperatures, about 400 degrees C, and let it crystalise and grow on your surface.
By controlling a few variables, you can use the deposition process to produce a layer of
carbon nanotubes, which are all stacked vertically on the surface.
It’s known as a Vertically Aligned NanoTube Array, or VANTA.
The result is a surface that absorbs up to 99.965% of all light falling on it.
This number has since been beaten by another material, developed at M.I.T., more recently
but the principles in both process are similar. They are amongst the blackest materials available.
So… what does that have to do with anything? Well, you might be thinking “Hey,
this Vantablack stuff would make an excellent material for an art project I have…”
…but the license for artistic use of it was granted exclusively to a guy called Anish Kapoor.
Kapoor is a multi-millionaire artist, probably most famous for being really annoyed that ‘The
Bean’ in Chicago gets called ‘The Bean’ and trying to stop people taking photos of it.
And he negotiated the sole use of one of world’s most interesting materials for artistic purposes.
That exclusivity really annoyed the art community, and led to many developments,
most notably in this case from Stuart Semple, who lets you buy his materials only on the condition
that you declare – in the terms of service – that you are not Anish Kapoor nor associated with him.
This trolling feud has been going a few years, I mean, the guy once hired a bouncer for an art show
whose only purpose was to kick Anish Kapoor out if he showed up. And its’ still on-going. If
you ever read a Twitter summary or some other social media post summing it up,
I guarantee you that there will be new developments after the post stops.
So that led to Black 3 being created, and not being Anish Kapoor, nor associated with him,
and with having no intentions of sending this paint on to him, I bought some.
Right, let’s take a look at this stuff. It’s very fancy. It’s like high-end perfume.
I think it’s the Black 2.0 that’s supposed to smell nice. This doesn’t really smell of anything.
So I’m just going to use a small amount. What you can see is that this is very, very thick
stuff, or viscous – as we might say – so that’s telling us that this is packed with pigment.
If you ever watch Bob Ross, his paints are very, very thick. They are not the flowing, watery
colours that you might expect from cheaper paint. So we’ll start with a little bit…
The coverage there is actually really good. That tells us it’s packed with whatever is making
this black. There’s a lot of it in there. It’ll probably need two coats, because it’s
going on to plastic, and we’ll come back and see what it looks like when there are two on there.
But, the liquid portion isn’t really sticking to the plastic. And that suggests that
whatever is in this is probably water-based. Water is polar. Plastic tends to be
apolar. They don’t mix very well. So, all this material’s performance
is not really within the chemistry, it’s within the formulation. That’s
the combination of what you have in here, and in what amounts.
If you have too much pigment, obviously, it will fall apart. It won’t form a paint.
If you have too much of the base, there won’t be any colour to it.
So the point of formulation chemistry is to get that balance right so you get the best performance
of your material. And a lot of super-materials, and “wonder materials”,
do fall apart at the formulation stage. And that’s because we can’t get it
to perform what we want, because we can’t mix it with the right materials.
So, sometimes, it’s back to the drawing board for a lot of chemists when they can’t
bring their wonder material to market because it won’t formulate properly.
It’s important, before we start, to point out that Semple’s Black 3 and Black 2 are not meant to be
black-black, like Vantablack… but matte blacks. They can’t be advertised as the blackest blacks,
but they can be described as perhaps the least reflective.
This lack of reflectivity is not so much a property of the colour,
but a property of the surface it creates.
When I first got interested in this, I thought you would put it on in a really thick layer,
and it would sort-of level itself to create the right surface. But it’s not. You have to put
this on very thinly and smoothly. We’ll see in a moment why that
might be.
There is some stuff in the fine print about Black 3.0 that you should put
it on in a single layer and wait for it to dry properly, otherwise it can be very unforgiving.
Because as I was saying earlier, it’s not just about the pigments in here, it’s about the
surface. The matte effect comes from the surface create, not necessarily the colours that are in
there. If you don’t let it dry correctly, that surface is not going to be correct.
I think this is enough to be getting on with. We’ll come back when it’s dry and a bit more done.
So, there are three different things we need to consider when looking at what makes a black paint,
or black material like these, work. There’s the specific frequencies
of light absorbed. How much light it absorbs.
And there’s what happens to any light that does get reflected back.
That last bit is the interesting bit, here. If you’ve done any high school physics,
you’ll understand that the angle of incidence equals the angle of reflection. So, if you have
a very, perfectly smooth, surface, all of the light reflected will be completely coherent.
In that case, you get a mirror. It not only reflects the vast majority of light,
absorbing very little, but it bounces it back perfectly, too.
This is known as specular reflection. If your surface scatters it back a
little less coherently, you’ll get a glossy look, instead. Here, you’ll see reflections
of probably only the brightest parts of the environment. And they’ll be a little bit blurred.
In physics, this is still reflection. It’s just less coherent.
In the art world, it’s often called a specular highlight.
These are interesting things in computer graphics, because the specular reflections are
often approximated separately, to give the shiny, reflective look,
but without the computer needing to do enormously complex calculations to create the blurred
reflection that a real glossy surface has. Then, if you scatter the light back with
absolutely no coherence, you get that matte effect. The reflected light is diffuse,
and you don’t see any shiny reflective highlights.
This usually happens because the surface is rough, but on a very small scale.
Angle of incidence still equals angle of reflection,
but the orientation of the surface isn’t constant, it isn’t flat. So light rays striking the surface,
even very close to each other, may shoot off into completely different directions.
So, something matte, like Black 3, is really good for applications where you want no shine, at all.
Something like Vantablack is going to be really good at that, because the rough structure of
the surface is at the nano-scale. Materials like velvet are also really good at this, you can feel
the roughness of velvet if you stroke it, and that contributes to its matte, light-absorbing effect.
So, now, I’m done. And this is dry. And what you can see is a lot of
really bright streaks through there. That’s actually the plastic showing through there if you
look very closely. But there are also bits there where the surface hasn’t quite levelled properly.
And that happens usually on the first coat of this stuff. But where it’s really dark,
here – run your finger over it – it’s not quite smooth, but it’s not quite abrasive.
So that tells me that this surface is very rough, but on a very small scale.
I think, what’s happening here is that it’s attempting to re-create a VANTA-like
surface. And I imagine that’s what a VANTA feels like, though I imagine the surface is a lot more
delicate and touching it would probably ruin it. So let’s try a second coat and see what happens.
That small amount from earlier covered all of this.
Let’s give it another go.
And what you might notice, if you can see it,
is where it’s wet it’s actually darker. Or at least appears darker.
And you might think “well, that’s a bit pointless. Why is this super-black colour actually darker
when it’s wet? Why does it dry lighter?” One of the reasons for that is that it’s
not really “darker” where it’s wet. It’s actually shiny. This paint is supposed to be matte. Where
it’s dry, it’s scattering light much more easily. Where it’s wet, it’s probably
reflecting more light, but more coherently, it’s producing that specular reflection.
So it’s scattering more light back, but where it’s really dark, it’s just not scattering it
into your eyes. And when it’s matte, it’s going to look the same shade from every direction.
You’re not going to get that shine, that says it’s reflecting a lot of light,
along with black patches. It will be the same colour throughout.
So, that’s the matte effect, and how the material reacts to light.
what about the chemistry of the colour? That’s the two other things.
First, what is colour?
If we look at a rainbow, we see a spectrum of colours from red, through orange,
yellow, through green, on to blue… and what’s happening here is that each hue is a different
frequency of light. Or a different wavelength. They’re measures of the same thing:
the energy of each packet of light. With red, we have a lower frequency,
a longer wavelength, and a lower energy. With blue or violet, we have higher frequency, a
shorter wavelength and a higher energy. The visible region, and most of the UV region,
are about the right energy to start pushing electrons around in molecules.
They can start chemical reactions because of this. So, in our eyes, we have chemical receptors,
and each picks up a different energy. We interpret these energies, in our heads, as red,
green or blue. And different combinations of them generate the other colours that we perceive.
That means, in order for a red object to look, well, red, it must absorb light that is
higher energy than the red region. If it doesn’t absorb it, it’s reflected back.
Similarly for blue: a blue object must absorb any light isn’t in the
blue region, and reflect back the blue light. And molecules do that because the electrons in
them exist in different energy levels. If it’s the right energy, the electrons absorb it, and
jump up to the next level. If that energy ’s too low, nothing happens.
With energy that’s too high, nothing happens. The light that is absorbed is reflected back in
the case of a surface, or transmitted through in the case of a translucent material or solution.
For a dye or pigment to be black, it’s got to absorb the
widest possible range of these energies, and as evenly as possible.
So, the important thing for black pigments is to absorb the broadest range of light.
They don’t always do this perfectly. Black pigments, when you look at them in strong
light, or next to other blacks, tend to look a little brown-ish, or blue-ish, or green-ish.
That’s because the absorption across the whole spectrum of light
isn’t equal, and some colours will come through. Black dyes are also sometimes made of mixtures
of different chemical materials that try and get that broadest range of absorption.
If that mix of material is not quite balanced, you’ll see some of that colour come through.
Even if that mix is very well-balanced, any change in the spectral distribution of the
incident light, can strongly change a colour, and that’s really pronounced with blacks,
where there’s a very thin margin for us to perceive a difference in colour.
There’s also a lot of complicated effects related to colour theory and the fact that colours are
really perceptions and interpretations made by our eyes and brains. You can make a surface appear
even darker if you simply put it next to a lighter surface for our eyes to compare it against.
Right… so this is it finished. Probably needs another bit of
touching up, because there’s parts where I haven’t quite covered it properly.
There’s no angle on this dry base plate that seems to reflect more light than
anywhere else. Your eye almost slips off it. It can’t be the darkest thing; it’s got to reflect
that 1 or 2 percent of light somewhere. But it does it in all sorts of directions. It’s not
sending out those coherent beams of specular light to make a reflection.
The final thing to look at is how much light these materials absorb.
This is sort of the simplest, and also the most complicated, part of the chemical physics.
Because you have your energy levels, and assume they’re spaced apart
just right to catch the right amount light… you still have to address the
issue of whether that transition from one state to another is very easy.
The more difficult it is for electrons to make this jump, the weaker the absorption, the less
light that’s taken in. If the jump is really easy, the material absorbs the light much more readily.
We can quantify that one in spectroscopy with a value known as the molar extinction coefficient,
a value that can actually tell us a lot about the nature of molecules. And first- and second-year
chemistry degrees usually give you a couple of opportunities to actually measure it.
We could be here for a long time discussing why some molecules absorb strongly, and others don’t.
I think this is probably just carbon-black. Really finely ground charcoal suspended in
a couple of binders, or something. If Stuart Semple ends up watching this,
and gets to this stage, feel free to correct me if that’s not the case. It certainly feels
like it. It doesn’t have a smell to it. And carbon and charcoal makes sense, it’s
very amorphous, it doesn’t have any regularity to. So it doesn’t have any regularity to the
energy levels in it. So, it’s not going to absorb one colour more than another. It’s very noisy.
Then you have it black-coloured instead of a specific colour.
And that’s a good property of carbon and charcoal. It’s why food that burns goes this
colour – because there’s a mix of things in there and it’s not very regular.
Overall, really good, really black paint, isn’t it.
So… that’s a whistlestop tour of some of the chemistry behind inks, dyes and pigments.
I haven’t even considered the chemical structures of them;
just what they need to do to make something black. This is important, because there are
lots of really useful applications for ultra-black materials. Especially in instruments that are
sensitive to light, like telescopes. If you coat the inside in one of
these very black paints, or can get your hands on the carbon nanotube versions,
you can get some great performance boosts because you have less stray light to deal with.
Though I’m just going to use it to mess around with.