Some kind of blue

Next week is time for the local Jazz Festival, and to prepare I switch my background music back to Miles’ iconic album. In addition, I have been made aware that I seem to be making blue my go-to color. On a slightly related note, it turns out that blue is a very hard color to make.

I spy, with my little eye, something blue…

It seems weird that blue would be hard to make. It’s so prominent in nature. The sky is blue. The ocean is blue. Blue jays are blue. Blue eyes are blue.

But as it turns out, blue pigment is very rare. Butterflies and birds with a blue color aren’t blue because their wings or feathers contain blue pigment, but because of nanostructures that reflect and diffract light in such a way that interference amplifies blue wavelengths, while cancelling out the others.

Butterfly wings aren’t actually blue, they’re just pretending to be. (Image Grover Schrayer/Flickr)

A blue pigment however, absorbs all wavelengths except blue. Light absorption occurs when a photon supplies an electron with enough energy to jump to a higher energy band. As red light has the lowest energy, only electrons with a narrow energy gap can be excited. Only a few molecules have the right structure for this to happen. Absorption of red light is crucial for a blue pigment, and therefore it’s a rare thing.

Blue light has enough energy to allow an electron to jump a larger energy gap then red light. Last time someone explained light absorption to me, they did it in the form of interpretive dance. It made so much sense.

Out of the blue

Because of their natural rarity, the design of synthetic blue pigments is of high interest for science and industry. The bluest blue was created by accident, by Mas Subramanian, a solid state chemist who wanted to create a material with the combination of electronic and magnetic properties for microchips. One of his ideas didn’t lead to anything particularly useful for fast computers, but it was very blue.

The bluest blue: YInMn (Photo by Ian Allan)

The blue dream

Where did this quest for blue originate? Blue is most people’s favorite color; it symbolizes depth, stability and serenity; and as it is the color of the sky and the sea, painters love it. True blue flowers are non-existent (violets are purple, people), even though horticulturists and scientists have tried endlessly. And even though blue food is unconsciously associated with toxins and spoilt food, some scientists’ life goal is to create true blue food coloring, rather than current food coloring that seems more green.

And I’m sure that Blue Man Group would appreciate a bluer skin. (Photo: Blue Man Group)

While artists, foodies, and flower lovers dream of the truest blue, I’ll go back to some sweet tunes and feeling slightly melancholic. I mean… Blue.


Read more about blue in this Science feature.

A close-knit bit of history

About a year ago, I took up knitting. I started simple and obvious by knitting a scarf.

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I made dis.

I then went on to knit a headband, a pair of arm warmers, and another headband. Currently, I am knitting a sweater. I guess you could say that I’m getting into the more advanced stuff – nevermind that it is the simplest sweater pattern ever*.

What I haven’t even dared think about knitting, is socks. Even though socks have been knitted for ages. And I really do mean ages. It may come to no surprise that the ancient Egyptians were a lot more talented than I am and that they were able to knit stripy socks. Exhibit A**: the 1700-year-old- stripy sock that recently made the news.

To be completely truthful, the sock was more likely a product of nailbinding, the precursor of knitting (also sometimes referred to as “knotless knitting”). The oldest evidence of true Egyptian knitting dates from between 1000 and 1400 A.D, so still pretty old.

By the way, Egyptian socks were pretty weird in the sense that they had a separate compartment for their big toe so they could wear sandals and flipflops.

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Remember the #Naughties when toe socks were okay? (I definitely had a pair of these monstrosities) 

Back to the 300 A.D. stripy sock:

Recently, scientists at the British Museum have refined a multispectrum imaging technique to study the chemical signatures that can be found in the threads. Importantly, this imaging technique is non-invasive, in contrast to other common techniques: no physical sample needs to be taken. Just by taking images using different types of light, information about the dyes that were used can be extracted.

Surprisingly, the number of dyes that were available to the knitter (m/f, who knows?) were limited; there were four dyes in the sock, probably derived from plants: madder (red), woad (blue), weld (yellow) and tannin (brownish). But people were creative, and remembered their kindergarten art lesson: to create more colors, you mix your base colors! The ancient Egyptians would use double and sequential dying, or twist fibers together, to expand the available hues and create the many stripes.

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An Egyptian child’s stripy sock in different lights, from the original article.

We know this because the researchers combined different types of light and imaging. Typically, when you take a picture with a standard camera, you are capturing the reflected visible light – as was done in panel (a) in the image. This gives you information about the colors that we can see with our eyes, i.e. “visible”, with wavelengths between ~ 400 and 700 nm. ***

By using light of different wavelengths, they learned more about the chemical properties of the sample. For example, by illuminating and capturing infrared light – with wavelengths over 700 nm (c, false-colored in d) – or ultraviolet (UV) light – with wavelengths under 400 nm (e, false-colored in f).

There’s one panel I left out… Materials do more than just reflect light, they also absorb light: transferring light energy into another type of energy. This energy can be heat, but it can also be re-emitted as light of a different wavelength than the incident light, a process called luminescence. An example of luminescence is the glow-in-the-dark (phosphorescent) stars I have on my ceiling. Another example, and more relevant to the sock, is taking a picture of the visible light while using UV-lighting, or UV-induced visible luminescence (b).

So each dye has in a unique “fingerprint,” a unique combination of signatures using these different types of light. Well, relatively unique – it’s science, everything is “known” with a certain statistical significance. In any case, this allows the British Museum scientists to make very educated guesses about what dyes were used, in which combinations, and in which amount.s

My sweater-to-be is going to be stripy too. Luckily for me, I can just go to a yarn shop and by a huge ball of wool (light blue) and some silver thread to add in for the lines. I don’t need to do any dying. And who knows, perhaps scientists 1700 years in the future will have some newer imaging technique and want to study my sweater?

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Bonus PDMS-lens picture of my sweater-to-be. Visible light, in case you were wondering.

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* basically 4 rectangles: two rectangles for the front and the back, two rectangles for the sleeves.

** There will be no Exhibit B.

*** Heyoooo, this history-post just got some physics knit into it!