From ancient Egyptian sarcophagi bathed in lapis lazuli to a synthetic pigment accidentally
created in a lab that’s already being patented and marketed as ‘the bluest blue ever,’
blue is the rarest—and perhaps the most celebrated—color on earth.
But why is it so hard to make and why are we are so enamored with it?
The science of blue pigment is what makes it minerally and biologically rare in nature
and incredibly difficult to recreate synthetically.
And its rarity, it’s special-ness, is what makes it so culturally significant throughout
all of human history.
Since about 6700 BCE, the first known usage of blue pigment by humans, blue was difficult
to get your hands on, and then hard to process for use as a paint or a dye.
This meant blue pigment was very expensive and valuable, only to be used for special
occasions and high art, making it the hallmark color of the wealthy, the royal, and the holy
from the very beginning of culture.
Despite its eventual role as a treasured part of our visual world, some linguists and historians
actually have a theory that maybe humans couldn’t see blue until relatively recently in our
history because a word for blue doesn’t occur in almost any ancient language. The
very first recorded society to have written down a word for blue were the ancient Egyptians
also coincidentally the first culture to produce a blue dye.
So it could be that the main blue things in our world—like the sky and the ocean—are so
huge, so all-encompassing, so ever-present, that it didn’t occur to us to describe their
color.
They are simply the sky and the sea, the origins of our world, stretching as far as we can
see.
And perhaps blue occurred so infrequently in the rest of the natural world, it just
never necessitated a word of its own.
But if its cultural significance is due to its scarcity, why is it so rare?
It all comes back down to the science.
First of all, almost everything in nature that looks blue is a lie.
The vast majority of living things actually can’t produce blue pigment.
The other bright colors we see in the wild, like the reds and oranges and yellows, are
colors an animal can become because of what they eat—they’re ingesting that pigment
and processing and recycling it to give them their color.
But most animals that seem blue to us—like this butterfly or this bird—actually aren’t.
And for the most part, with this notable exception, it’s not because of what they’re eating.
Many blue animals actually have color built into their architecture instead—the blue
that we see here is actually due to microstructures in the feathers or scales of these creatures,
which structurally filter out all wavelengths but blue, almost like a tiny prism tricking
you into seeing a color that isn’t caused by pigment.
That’s even the case for our blue irises—it's microstructure, not pigment!
And it’s not just the animal kingdom that has workarounds—’true’ blue is equally
rare in plants.
Some plants do produce pigments called anthocyanins, but none of these are actually blue.
Instead, plants can tweak the pH and arrangement of the molecules of a red anthocyanin pigment
to reflect different wavelengths of light to produce blue-tinged flowers. But this
is pretty rare.
Many of our common decorative flowers, like roses and tulips and carnations, just don’t
make blue.
We can put them in artificially dyed water to get an unnatural-looking glow, but scientists
are also trying to modify these flowers to get them to produce blue naturally.
One team was successful at making blue chrysanthemums, but whoa was it hard, and involved
extremely detailed and finicky metabolic engineering.
But why?
What about blue makes it so tricky and special?
There’s no one straight answer, but the key probably lies inside the physics of pigments.
To make a true color with no shortcuts, an organism has to produce a pigment, which, if
we’re gonna define it technically, is a compound that absorbs some wavelengths of
visible light and reflects the one we’re seeing.
Now, as we know, light is a kind of energy.
A pigment that absorbs a certain wavelength of light has to absorb that light energy and
then has to do something with it, has to put it somewhere.
That usually means that electrons in that pigment get bumped up to a higher energy level,
called an orbital.
So if we picture the pigment as including a cloud of electrons on different rungs, a
photon of light can bump an electron up another orbital, but the amount of energy coming in
from that light has to match the distance between orbitals.
This is actually the fundamental reason that different pigments look differently colored:
each different pigment compound has a differently sized energy gap between orbitals, and can
only absorb specific wavelengths of light that will excite an electron enough to jump
over that gap.
The pigment needs to have the right atomic structure and electron arrangement to absorb
certain wavelengths, leaving the other wavelength to bounce off the pigment and hit us in the
eyeball.
I know, I’m right there with you—I was very surprised, but delighted, to learn that
color has this much physics involved.
So, where does all this subatomic dancing leave us when it comes to blue?
Well, to look blue to the observer, remember that a pigment has to absorb wavelengths that
aren’t blue.
Which means that, among other wavelengths, that pigment needs to absorb red light.
Red is the lowest energy level wavelength on the spectrum of visible light.
And that means that the orbitals need to be uncomfortably close together for red light
to push an electron from one orbital to the next because red, well, doesn’t have a
lot of energy.
And this kind of molecule with close-together scrunched up orbitals is apparently very difficult
to make.
Blue’s rarity is due to its science. Its rarity is its allure.
And aside all from the psychological theories about our attraction to blue being because
it makes us feel calm, pigment science may have surprisingly important applications outside
of art, design, and flower arrangements.
Pigments like anthocyanins are antioxidants and are antimicrobial, and some scientists
are researching how they could be incorporated into health-boosting foods.
Structural pigments like the ones in butterfly wings could lead to the development of colors
that we could grow, kinda like how you grow sugar crystals, with applications from industrial
‘paints’ to cosmetics that don’t require animal testing.
So blue is much more than just pretty, but it plays pretty hard to get.
And I have a feeling we’ll probably keep chasing it down for quite a long time.
What do you think?
Why is blue so fascinating and precious to us?
Let us know down in the comments below, and make sure you subscribe to Seeker to tag along
as we explore the world around us.
Thanks for watching.