Tag Archives: iridescence

Colour: an art/science open call for submissions

The submission deadline for this open ‘art/sci’ call is January 17, 2018 (from a November 29, 2017 Art/Science Salon announcement; received via email),


An exhibition exploring colour as a phenomenon that crosses the
boundaries of the arts and sciences.

Artists and designers revel in, and seek to understand, the visceral,
physical and ephemeral qualities of colour. Sir Isaac Newton began his
scientific experiments with light and prisms as ‘a very pleasing
divertisement, to view the vivid and intense colours produced
thereby’. His investigations ultimately changed our understanding of
the fundamental nature of light and colour. Johann Wolfgang von Goethe
challenged Newton’s understanding as limited, and introduced colour as
an emotionally charged phenomenon. He proposed an alternative
methodological approach based on ’empathic observation’.

COLOUR: WHAT DO YOU MEAN BY THAT? calls for art inspired by, or
questioning, scientific concepts about colour: art that encapsulates
colour knowledge from multiple perspectives.

We are not looking for the merely colourful – rather we look for work
engaging ideas, theories and aspects of colour – both conceptual and
physical – that highlight colour knowledge as richly meaningful across
diverse ways of knowing.

To this end, we invite proposals that present, consider, or respond to
research about colour and colour phenomena. Work may relate to:

* physical colour phenomena, e.g. light sources, interference,
iridescence, scattering, reflection
* chemistry of dyes & pigments
* colour vision / colour perception
* colour renderings of energies outside of the visible spectrum
(ultraviolet, infra-red, etc.)
* colour meanings (cultural, scientific, philosophical)
* cross-sensory colour sensations and understandings
* colour theories
* colour histories

SHOW DATES: MARCH 7-25, 2018.

COLOUR: WHAT DO YOU MEAN BY THAT? is jointly sponsored by Propeller
Gallery and the Colour Research Society of Canada [1]

SHOW LOCATION: Propeller Gallery, 30 Abell St, Toronto, ON, Canada

SUBMISSION DEADLINE: Wed Jan 17, 2018, 11:59pm [which timezone?]



You may submit more than one submission, provided the concept is
substantially different for each piece, with a maximum of three
submissions. With each submission, please provide at least one image
(maximum 4 images) relevant to your proposal.

Details about yourself and your work including:

* Name, address, email, phone number, with a brief bio.
* Title of Work, Year, Medium, Size and Value in $CAD.
* A brief written statement about the work, including how the work
deals with, or draws its inspiration from, diverse ways of knowing about
colour (max. 150 words).

CURATORIAL TEAM MEMBERS: Doreen Balabanoff, Robin Kingsburgh, Janet
Read, Judith Tinkl


* 25% commission collected on any work sold as a result of this
* For more information visit our website: www.propellerctr.com [3]
* If selected, you agree to allow us to use your submission material,
without compensation, in any potential catalogue/publication for this
* Selected artists will be contacted by email not later than January
31. Delivery instructions will be given at that time.
* An event at the exhibition, related to International Colour Day,
March 21st, will be announced in early 2018.

Please direct inquiries to:

Nathan Heuvingh
Gallery Director

Facebook: https://www.facebook.com/PropellerTO/ [4]
Twitter: @PropellerTO
Instagram: @propellerygallery_to

The co-sponsor for this upcoming exhibition, the Colour Research Society of Canada has a website that proved to be a delightful surprise.

Getting back to COLOUR: WHAT DO YOU MEAN BY THAT?, good luck with your submission, and should it be accepted, good luck with sales!

Vancouver (Canada) -based NanoTech Security and its tireless self-promotion

First featured here in a January 17, 2011 posting about proposed anti-counterfeiting measures based on the structures present on the Blue Morpho butterfly’s wings, NanoTech Security is the subject of a profile in the Vancouver (Canada) Sun’s Dec. 28, 2015 Technology article by Randy Shore.

They’ve managed to get themselves into the newspaper without having any kind of real news, research or business, to share. As is so often the case, timing is everything. This is a low news period (between Christmas and New Year) and the folks at NanoTech Security got lucky with a reporter who doesn’t know much about the company or the technology. When you add in low public awareness about the company and its products (you couldn’t do this with a company specializing in a well established technology, e.g., smartphones), there’s an opportunity.

Getting back to Shore’s Dec. 28, 2015 Technology article in the Vancouver Sun,

Landrock [Clint Landrock], the chief technology officer at Burnaby-based [Burnaby is a municipality in what’s known as Metro Vancouver] Nanotech Security Corp., has spun off his SFU [Simon Fraser University] research to found the firm, which is developing nano-optics for the global battle against counterfeiters.

Colour-shifting holographic images, used as counterfeit protection on many banknotes, use technology that has been around for more than 35 years and they are increasingly easy to reproduce. Talented hobbyists can duplicate simple holographic features and organized criminals with deeper pockets can reproduce more sophisticated features with the right equipment.

Nanotech Security hopes to take a quantum leap ahead of forgers.

The detail and colour reproduction possible in Nanotech’s KolourOptick are dramatically better than the holographic images used on banknotes.

“We can improve a lot on those, by making the image a lot brighter, have a lot more detail and make it easy to view,” said Landrock. “When you try to fake that, it’s much more difficult to do and when you see a fake it looks fake.”

“Right now, the fake holograms often look better than the real thing,” he said.

Tiny structuresWhat [sic] Landrock found on the wings of the Blue Morpho was a lattice of tiny treelike structures that interact with light, selecting certain wavelengths to create a bright blue hue without pigments.

This ‘origins’ story includes a business mastermind, Doug Blakeway, and the researcher (Bozena Kaminska) under whose supervision Landrock did his work. Blakeway provides a somewhat puzzling quote for Shore’s story,

“I love nanotechnology, but I really have not seen a commercialization of it that can make you money in the near term, [emphasis mine]” said Blakeway. “When this was initially presented to me by Bozena and Clint, I immediately saw their vision and they were only after one application — creating anti-counterfeiting features for banknotes.”

The three formed a private company and licensed the patents from SFU, which receives a three per cent royalty on sales of the technology created under its roof. …

I am perplexed by Blakeway’s ” … I really have not seen a commercialization of it that can make you money in the near term” comment. There are many nanotechnology-enabled products on the market ranging from coatings for superhydrophobic waterproofing products to carbon fibre-enhanced golf clubs to nanoscale chips for computers and components for phones to athletic materials impregnated with silver nanoparticles for their antibacterial properties (clothes you don’t have to wash as often) to cosmetics and beauty products, e.g., nano sunscreens, and there are more.

NanoTech Security’s recently released some information about their financial status. They must feel encouraged by their gains and other business developments (from a Dec. 17, 2015 NanoTech Security news release),

Nanotech Security Corp. (TSXV: NTS) (OTCQX: NTSFF), (“Nanotech” or the “Company”) today released its financial results for the fourth quarter and year ended September 30, 2015.

Strategic Highlights from 2015

Revenue increased to $5.2 million a 131% increase over 2014. Security Features contributed revenues of $3.1 million.
Gross margin improved to 43% up from 34% in the same period last year. The improvement reflects the increased mix of higher margin Security Features revenue.
Signed two banknote security feature development contracts. The contracts are with top ten issuing authorities to develop unique optically-variable security features for incorporation into future banknotes.
Strategic meetings with large international banknote issuing authority. The Company has been approached by a large international banknote issuing authority to deliver a large volume of Optical Thin Film (“OTF”), and partner with our KolourOptik™ technology. Management continues to devote a significant amount of time and resources in advancing these opportunities.
Private Placement. The Company completed a non-brokered private placement financing of $2.6 million in equity units at $1.00 each.
Signed an amending agreement related to the 2014 Fortress Optical purchase agreement. The amendment provides that 1.5 million of the 3.0 million shares held in escrow, pending certain sales milestones were released from escrow and the remaining 1.5 million shares were returned to the treasury. The overall effect of the amendment resulted in a gain of $1.5 million and cancellation of 1.5 million shares.
Demonstrated KolourOptik™ security feature on metal coins. The Company successfully applied nanotechnology images to metal coins in a production environment at an issuing mint.
Granted five new patents expanding the growing IP portfolio. Three patents relate to the Company’s next generation nanotechnology authentication features, and two provide increased protection for OTF.

I’m curious as to how much of their revenue is derived from sales as opposed to research funding and just how much money does a 43% increase in gross margins represent? (Or, perhaps I just need to get better at reading news about *companies* and their finances.) In any event, signing two contracts and gaining interest in applying the technology to metal coins must have been exciting.

This story goes to show that if you understand news cycles, have a little luck and/or know someone, and have a relatively unknown technology or product, it’s possible to get media coverage.

*’company’s’ corrected to ‘companies’.

Clues as to how mother of pearl is made

Iridescence seems to fascinate scientists and a team at Cornell University is no exception (from a Dec. 4, 2015 news item on Nanowerk),

Mother nature has a lot to teach us about how to make things.

With that in mind, Cornell researchers have uncovered the process by which mollusks manufacture nacre – commonly known as “mother of pearl.” Along with its iridescent beauty, this material found on the insides of seashells is incredibly strong. Knowing how it’s made could lead to new methods to synthesize a variety of new materials with as yet unguessed properties.

“We have all these high-tech facilities to make new materials, but just take a walk along the beach and see what’s being made,” said postdoctoral research associate Robert Hovden, M.S. ’10, Ph.D. ’14. “Nature is doing incredible nanoscience, and we need to dig into it.”

A Dec. 4, 2015 Cornell University news release by Bill Steele, which originated the news item, expands on the theme,

Using a high-resolution scanning transmission electron microscope (STEM), the researchers examined a cross section of the shell of a large Mediterranean mollusk called the noble pen shell or fan mussel (Pinna nobilis). To make the observations possible they had to develop a special sample preparation process. Using a diamond saw, they cut a thin slice through the shell, then in effect sanded it down with a thin film in which micron-sized bits of diamond were embedded, until they had a sample less than 30 nanometers thick, suitable for STEM observation. As in sanding wood, they moved from heavier grits for fast cutting to a fine final polish to make a surface free of scratches that might distort the STEM image.

Images with nanometer-scale resolution revealed that the organism builds nacre by depositing a series of layers of a material containing nanoparticles of calcium carbonate. Moving from the inside out, these particles are seen coming together in rows and fusing into flat crystals laminated between layers of organic material. (The layers are thinner than the wavelengths of visible light, causing the scattering that gives the material its iridescence.)

Exactly what happens at each step is a topic for future research. For now, the researchers said in their paper, “We cannot go back in time” to observe the process. But knowing that nanoparticles are involved is a valuable insight for materials scientists, Hovden said.

Here’s an image from the researchers,

Electron microscope image of a cross-section of a mollusk shell. The organism builds its shell from the inside out by depositing layers of calcium carbonate nanoparticles. As the particle density increases over time they fuse into large flat crystals embedded in layers of organic material to form nacre. Courtesy: Cornell University

Electron microscope image of a cross-section of a mollusk shell. The organism builds its shell from the inside out by depositing layers of calcium carbonate nanoparticles. As the particle density increases over time they fuse into large flat crystals embedded in layers of organic material to form nacre. Courtesy: Cornell University

Here’s a link to and a citation for the paper,

Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells by Robert Hovden, Stephan E. Wolf, Megan E. Holtz, Frédéric Marin, David A. Muller, & Lara A. Estroff. Nature Communications 6, Article number: 10097 doi:10.1038/ncomms10097 Published 03 December 2015

This is an open access paper.

Structural colo(u)r with a twist

There’s a nice essay about structural colour on the Duke University website (h/t Nanowerk). Long time readers know my favourite piece of writing on the subject is by Cristina Luiggi for The Scientist magazine which I profiled here in a Feb. 7, 2013 posting.

This latest piece seems to have been written by Beverley Glover and Anika Radiya-Dixit and it is very good. From the Oct. 27, 2015 Duke University blog posting titled, Iridescent Beauty: Development, function and evolution of plant nanostructures that influence animal behavior,

Iridescent wings of a Morpho butterfly

Creatures like the Morpho butterfly on the leaf above appear to be covered in shimmering blue and green metallic colors. This phenomenon is called “iridescence,” meaning that color appears to change as the angle changes, much like soap bubbles and sea shells.

In animals, the physical mechanisms and function of structural color have been studied significantly as a signal for recognition or mate choice.

Glover, one of the post’s authors, is a scientist who believes there may be another reason for iridescence,

On the other hand, Beverley Glover believes that such shimmering in plants can actually influence animal behavior by attracting pollinators better than their non-iridescent counterparts. Glover,Director of Cambridge University Botanic Garden,  presented her study during the Biology Seminar Series in the French Family Science Center on Monday [Oct. 26, 2015] earlier this week.

Hibiscus Trionum

The metallic property of flowers like the Hibiscus Trionum above are generated by diffraction grating – similar to the way CD shines – to create color from transparent material.

In order to observe the effects of the iridescence on pollinators like bees, Glover created artificial materials with a surface structure of nanoscale ridges, similar to the microscopic view of a petal’s epidermal surface below.

Nanoscale ridges on a petal's epidermal surface.

In the first set of experiments, Glover and her team marked bees with paint to follow their behavior as they set the insects to explore iridescent flowers. Some were covered in a red grating – containing a sweet solution as a reward – and others with a blue iridescent grating – containing a sour solution as deterrent. The experiment demonstrated that the bees were able to detect the iridescent signal produced by the petal’s nanoridges, and – as a result – correctly identified the rewarding flowers.

It’s worth reading the Oct. 27, 2015 Duke University blog posting to just to see the pictures used to illustrate the ideas and to find out about the second experiment.

Solving an iridescent mystery could lead to quantum transistors

iridescence has fascinated me (and scores of other people) since early childhood and it’s fascinating to note that scientists seems almost as enchanted as we amateurs are. The latest bit of ‘iridescent’ news comes from the University of Michigan in a Dec. 5, 2014 news item on ScienceDaily,

An odd, iridescent material that’s puzzled physicists for decades turns out to be an exotic state of matter that could open a new path to quantum computers and other next-generation electronics.

Physicists at the University of Michigan have discovered or confirmed several properties of the compound samarium hexaboride that raise hopes for finding the silicon of the quantum era. They say their results also close the case of how to classify the material–a mystery that has been investigated since the late 1960s.

A Dec. 5, 2014 University of Michigan news release, which originated the news item, provides more details about the mystery and the efforts to resolve it,

The researchers provide the first direct evidence that samarium hexaboride, abbreviated SmB6, is a topological insulator. Topological insulators are, to physicists, an exciting class of solids that conduct electricity like a metal across their surface, but block the flow of current like rubber through their interior. They behave in this two-faced way despite that their chemical composition is the same throughout.

The U-M scientists used a technique called torque magnetometry to observe tell-tale oscillations in the material’s response to a magnetic field that reveal how electric current moves through it. Their technique also showed that the surface of samarium hexaboride holds rare Dirac electrons, particles with the potential to help researchers overcome one of the biggest hurdles in quantum computing.

These properties are particularly enticing to scientists because SmB6 is considered a strongly correlated material. Its electrons interact more closely with one another than most solids. This helps its interior maintain electricity-blocking behavior.

This deeper understanding of samarium hexaboride raises the possibility that engineers might one day route the flow of electric current in quantum computers like they do on silicon in conventional electronics, said Lu Li, assistant professor of physics in the College of Literature, Science, and the Arts and a co-author of a paper on the findings published in Science.

“Before this, no one had found Dirac electrons in a strongly correlated material,” Li said. “We thought strong correlation would hurt them, but now we know it doesn’t. While I don’t think this material is the answer, now we know that this combination of properties is possible and we can look for other candidates.”

The drawback of samarium hexaboride is that the researchers only observed these behaviors at ultracold temperatures.

Quantum computers use particles like atoms or electrons to perform processing and memory tasks. They could offer dramatic increases in computing power due to their ability to carry out scores of calculations at once. Because they could factor numbers much faster than conventional computers, they would greatly improve computer security.

In quantum computers, “qubits” stand in for the 0s and 1s of conventional computers’ binary code. While a conventional bit can be either a 0 or a 1, a qubit could be both at the same time—only until you measure it, that is. Measuring a quantum system forces it to pick one state, which eliminates its main advantage.

Dirac electrons, named after the English physicist whose equations describe their behavior, straddle the realms of classical and quantum physics, Li said. Working together with other materials, they could be capable of clumping together into a new kind of qubit that would change the properties of a material in a way that could be measured indirectly, without the qubit sensing it. The qubit could remain in both states.

While these applications are intriguing, the researchers are most enthusiastic about the fundamental science they’ve uncovered.

“In the science business you have concepts that tell you it should be this or that and when it’s two things at once, that’s a sign you have something interesting to find,” said Jim Allen, an emeritus professor of physics who studied samarium hexaboride for 30 years. “Mysteries are always intriguing to people who do curiosity-driven research.”

Allen thought for years that samarium hexaboride must be a flawed insulator that behaved like a metal at low temperatures because of defects and impurities, but he couldn’t align that with all of its other properties.

“The prediction several years ago about it being a topological insulator makes a lightbulb go off if you’re an old guy like me and you’ve been living with this stuff your whole life,” Allen said.

In 2010, Kai Sun, assistant professor of physics at U-M, led a group that first posited that SmB6 might be a topological insulator. He and Allen were also involved in seminal U-M experiments led by physics professor Cagliyan Kurdak in 2012 that showed indirectly that the hypothesis was correct.

“But the scientific community is always critical,” Sun said. “They want very strong evidence. We think this experiment finally provides direct proof of our theory.”

Here’s a link to and a citation for the researchers’ latest paper,

Two-dimensional Fermi surfaces in Kondo insulator SmB6 by G. Li, Z. Xiang, F. Yu, T. Asaba, B. Lawson, P. Cai1, C. Tinsman, A. Berkley, S. Wolgast, Y. S. Eo, Dae-Jeong Kim, C. Kurdak, J. W. Allen, K. Sun, X. H. Chen, Y. Y. Wang, Z. Fisk, and Lu Li. Science 5 December 2014: Vol. 346 no. 6214 pp. 1208-1212 DOI: 10.1126/science.1250366

This paper is behind a paywall.

Nanocellulose and an intensity of structural colour

I love the topic of structural colour (or color, depending on your spelling preferences) and have covered it many times and in many ways. One of the best pieces I’ve encountered about structural colour (an article by Christina Luiggi for The Scientist provided an overview of structural colour as it’s found in plants and animals) was featured in my Feb. 7, 2013 posting. If you go to my posting, you’ll find a link to Luiggi’s article which I recommend reading in its entirety if you have the time.

As for this latest nanocellulose story, a June 13, 2014 news item on Nanowerk describes University of Cambridge (UK) research into films and structural colour,

Brightly-coloured, iridescent films, made from the same wood pulp that is used to make paper, could potentially substitute traditional toxic pigments in the textile and security industries. The films use the same principle as can be seen in some of the most vivid colours in nature, resulting in colours which do not fade, even after a century.

Some of the brightest and most colourful materials in nature – such as peacock feathers, butterfly wings and opals – get their colour not from pigments, but from their internal structure alone.

Researchers from the University of Cambridge have recreated a similar structure in the lab, resulting in brightly-coloured films which could be used for textile or security applications.

A June 13, 2014 University of Cambridge news release, which originated the news item, describe the phenomenon of structural colour as it applies to cellulose materials,

In plants such as Pollia condensata, striking iridescent and metallic colours are the result of cellulose fibres arranged in spiral stacks, which reflect light at specific wavelengths. [emphasis mine]

Cellulose is made up of long chains of sugar molecules, and is the most abundant biomass material in nature. It can be found in the cells of every plant and is the main compound that gives cell walls their strength.

The news release goes on to provide a brief description of the research,

The researchers used wood pulp, the same material that is used for producing paper, as their starting material. Through manipulating the structure of the cellulose contained in the wood pulp, the researchers were able to fabricate iridescent colour films without using pigments.

To make the films, the researchers extracted cellulose nanocrystals from the wood pulp. When suspended in water, the rod-like nanocrystals spontaneously assemble into nanostructured layers that selectively reflect light of a specific colour. The colour reflected depends on the dimensions of the layers. By varying humidity conditions during the film fabrication, the researchers were able to change the reflected colour and capture the different phases of the colour formation.

Cellulose nanocrystals (CNC) are also known as nanocrystalline cellulose (NCC).

Here’s a link to and a citation for  the paper,

Controlled, Bio-inspired Self-Assembly of Cellulose-Based Chiral Reflectors by Ahu Gumrah Dumanli, Gen Kamita, Jasper Landman, Hanne van der Kooij, Beverley J. Glover, Jeremy J. Baumberg, Ullrich Steiner, and Silvia Vignolini. Optical Materials Article first published online: 30 MAY 2014 DOI: 10.1002/adom.201400112

© 2014 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

While the researchers have supplied an image of the Pollia condensata, I prefer this one, which is also featured in my Feb. 7, 2013 posting,

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from http://www.the-scientist.com/?articles.view/articleNo/34200/title/Color-from-Structure/]

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from http://www.the-scientist.com/?articles.view/articleNo/34200/title/Color-from-Structure/]

Stunning, non?

Structural color and cephalopods at the University of California Santa Barbara

I last wrote about structural color in a Feb.7, 2013 posting featuring a marvelous article on the topic by Cristina Luiggi in the The Scientist. As for cephalopods, one of my favourite postings on the topic is a Feb. 1, 2013 posting which features the giant squid, a newly discovered animal of mythical proportions that appears golden in its native habitat in the deep, deep ocean. Happily, there’s a July 25, 2013 news item on Nanowerk which combines structural color and squid,

Color in living organisms can be formed two ways: pigmentation or anatomical structure. Structural colors arise from the physical interaction of light with biological nanostructures. A wide range of organisms possess this ability, but the biological mechanisms underlying the process have been poorly understood.

Two years ago, an interdisciplinary team from UC Santa Barbara [University of California Santa Barbara a.k.a. UCSB] discovered the mechanism by which a neurotransmitter dramatically changes color in the common market squid, Doryteuthis opalescens. That neurotransmitter, acetylcholine, sets in motion a cascade of events that culminate in the addition of phosphate groups to a family of unique proteins called reflectins. This process allows the proteins to condense, driving the animal’s color-changing process.

The July 25, 2013 UC Santa Barbara news release (also on EurekAlert), which originated the news item, provides a good overview of the team’s work to date and the new work occasioning the news release,

Now the researchers have delved deeper to uncover the mechanism responsible for the dramatic changes in color used by such creatures as squids and octopuses. The findings –– published in the Proceedings of the National Academy of Science, in a paper by molecular biology graduate student and lead author Daniel DeMartini and co-authors Daniel V. Krogstad and Daniel E. Morse –– are featured in the current issue of The Scientist.

Structural colors rely exclusively on the density and shape of the material rather than its chemical properties. The latest research from the UCSB team shows that specialized cells in the squid skin called iridocytes contain deep pleats or invaginations of the cell membrane extending deep into the body of the cell. This creates layers or lamellae that operate as a tunable Bragg reflector. Bragg reflectors are named after the British father and son team who more than a century ago discovered how periodic structures reflect light in a very regular and predicable manner.

“We know cephalopods use their tunable iridescence for camouflage so that they can control their transparency or in some cases match the background,” said co-author Daniel E. Morse, Wilcox Professor of Biotechnology in the Department of Molecular, Cellular and Developmental Biology and director of the Marine Biotechnology Center/Marine Science Institute at UCSB.

“They also use it to create confusing patterns that disrupt visual recognition by a predator and to coordinate interactions, especially mating, where they change from one appearance to another,” he added. “Some of the cuttlefish, for example, can go from bright red, which means stay away, to zebra-striped, which is an invitation for mating.”

The researchers created antibodies to bind specifically to the reflectin proteins, which revealed that the reflectins are located exclusively inside the lamellae formed by the folds in the cell membrane. They showed that the cascade of events culminating in the condensation of the reflectins causes the osmotic pressure inside the lamellae to change drastically due to the expulsion of water, which shrinks and dehydrates the lamellae and reduces their thickness and spacing. The movement of water was demonstrated directly using deuterium-labeled heavy water.

When the acetylcholine neurotransmitter is washed away and the cell can recover, the lamellae imbibe water, rehydrating and allowing them to swell to their original thickness. This reversible dehydration and rehydration, shrinking and swelling, changes the thickness and spacing, which, in turn, changes the wavelength of the light that’s reflected, thus “tuning” the color change over the entire visible spectrum.

“This effect of the condensation on the reflectins simultaneously increases the refractive index inside the lamellae,” explained Morse. “Initially, before the proteins are consolidated, the refractive index –– you can think of it as the density –– inside the lamellae and outside, which is really the outside water environment, is the same. There’s no optical difference so there’s no reflection. But when the proteins consolidate, this increases the refractive index so the contrast between the inside and outside suddenly increases, causing the stack of lamellae to become reflective, while at the same time they dehydrate and shrink, which causes color changes. The animal can control the extent to which this happens –– it can pick the color –– and it’s also reversible. The precision of this tuning by regulating the nanoscale dimensions of the lamellae is amazing.”

Another paper by the same team of researchers, published in Journal of the Royal Society Interface, with optical physicist Amitabh Ghoshal as the lead author, conducted a mathematical analysis of the color change and confirmed that the changes in refractive index perfectly correspond to the measurements made with live cells.

A third paper, in press at Journal of Experimental Biology, reports the team’s discovery that female market squid show a set of stripes that can be brightly activated and may function during mating to allow the female to mimic the appearance of the male, thereby reducing the number of mating encounters and aggressive contacts from males. The most significant finding in this study is the discovery of a pair of stripes that switch from being completely transparent to bright white.

“This is the first time that switchable white cells based on the reflectin proteins have been discovered,” Morse noted. “The facts that these cells are switchable by the neurotransmitter acetylcholine, that they contain some of the same reflectin proteins, and that the reflectins are induced to condense to increase the refractive index and trigger the change in reflectance all suggest that they operate by a molecular mechanism fundamentally related to that controlling the tunable color.”

Could these findings one day have practical applications? “In telecommunications we’re moving to more rapid communication carried by light,” said Morse. “We already use optical cables and photonic switches in some of our telecommunications devices. The question is –– and it’s a question at this point –– can we learn from these novel biophotonic mechanisms that have evolved over millions of years of natural selection new approaches to making tunable and switchable photonic materials to more efficiently encode, transmit, and decode information via light?”

In fact, the UCSB researchers are collaborating with Raytheon Vision Systems in Goleta to investigate applications of their discoveries in the development of tunable filters and switchable shutters for infrared cameras. Down the road, there may also be possible applications for synthetic camouflage. [emphasis mine]

There is at least one other research team (the UK’s University of Bristol) considering the camouflage strategies employed cephalopods and, in their case,  zebra fish as noted in my May 4, 2012 posting, Camouflage for everyone.

Getting back to cephalopod in hand, here’s an image from the UC Santa Barbara team,

This shows the diffusion of the neurotransmitter applied to squid skin at upper right, which induces a wave of iridescence traveling to the lower left and progressing from red to blue. Each object in the image is a living cell, 10 microns long; the dark object in the center of each cell is the cell nucleus. [downloaded from http://www.ia.ucsb.edu/pa/display.aspx?pkey=3076]

This shows the diffusion of the neurotransmitter applied to squid skin at upper right, which induces a wave of iridescence traveling to the lower left and progressing from red to blue. Each object in the image is a living cell, 10 microns long; the dark object in the center of each cell is the cell nucleus. [downloaded from http://www.ia.ucsb.edu/pa/display.aspx?pkey=3076]

Fro papers currently available online, here are links and citations,

Optical parameters of the tunable Bragg reflectors in squid by Amitabh Ghoshal, Daniel G. DeMartini, Elizabeth Eck, and Daniel E. Morse. doi: 10.1098/​rsif.2013.0386 J. R. Soc. Interface 6 August 2013 vol. 10 no. 85 20130386

The Royal Society paper is behind a paywall until August 2014.

Membrane invaginations facilitate reversible water flux driving tunable iridescence in a dynamic biophotonic system by Daniel G. DeMartini, Daniel V. Krogstadb, and Daniel E. Morse. Published online before print January 28, 2013, doi: 10.1073/pnas.1217260110
PNAS February 12, 2013 vol. 110 no. 7 2552-2556

The Proceedings of the National Academy of Sciences (PNAS) paper (or the ‘Daniel’ paper as I prefer to think of it)  is behind a paywall.

Structure of color

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from http://www.the-scientist.com/?articles.view/articleNo/34200/title/Color-from-Structure/]

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from http://www.the-scientist.com/?articles.view/articleNo/34200/title/Color-from-Structure/]

Hard to believe those berries were collected more than four decades ago, according to Cristina Luiggi in her Feb. 1, 2013 article, Color from Structure, for The Scientist magazine. Her focus is on biological nanostructures and it is a fascinating article which I urge you to read in its entirety if you have the time and this kind of thing interests you. As you can see, the pictures are great.

Here are a few excerpts from the piece,

Colors may be evolution’s most beautiful accident. Spontaneous mutations that perturbed the arrangement of structural components, such as cellulose, collagen, chitin, and keratin, inadvertently created nanoscale landscapes that catch light in the most vibrantly diverse ways—producing iridescent greens, fiery reds, brilliant blues, opalescent whites, glossy silvers, and ebony blacks.

Structural colors, in contrast to those produced by pigments or dyes, arise from the physical interaction of light with biological nanostructures. These color-creating structures likely developed as an important phenotype during the Cambrian explosion more than 500 million years ago, when organisms developed the first eyes and the ability to detect light, color, shade, and contrast. “As soon as you had visual predators, there were organisms that were either trying to distract, avoid, or communicate with those predators using structural coloration,” says Yale University evolutionary ornithologist Richard Prum.

Ever since, structural coloration has evolved multiple times across the tree of life, as a wide range of organisms developed ways to fine-tune the geometry of some of the most abundant (and often colorless) biomaterials on Earth, engineering grooves, pockets, and films that scatter light waves and cause them to interfere with each other in ways we humans happen to find aesthetically pleasing.

Here’s why color derived from structure doesn’t fade, from Luiggi’s article,

Pigments and dyes are molecules that produce colors by the selective absorption and reflection of specific wavelengths of electromagnetic radiation. Structural colors, on the other hand, rely exclusively on the shape of the material and not its chemical properties. While pigments and dyes degrade and their colors fade over time, some types of structural coloration, which rely on the same materials that make up tree bark, insect exoskeletons, and claws or nails, can persist hundreds, thousands, and even millions of years after the death of the organism.

Structural color can be found in a lot of plant life,

Although there are only a handful of known examples of structural colors in fruits, there are plenty to be found in the leaves and petals of plants. Within every family of flowering plants, there is at least one species that displays structural colors.

“The presence of structural colors, especially in flowers, is likely used by pollinators to spot the position of the flower and to recognize it better,” Vignolini [Silvia Vignolini, a physics postdoc at the University of Cambridge] explains. But in some plants, the evolutionary purpose of structural coloration is harder to pin down. The leaves of the low-lying tropical spikemoss Selaginella willdenowii, for example, produce blue-green iridescence when young and growing in the shade, and tend to lose the structural coloration with age and when exposed to high levels of light. The iridescence is achieved by cells in the leaves’ upper epidermis, which contain a few layers of cellulose microfibrils packed with different amounts of water. This ultrastructure is often absent in the leaves of the same species growing in direct sunlight. Researchers hypothesize that the spikemoss turns off its iridescence by changing the water content of the leaves’ cell walls, says Heather Whitney, a research fellow at the University of Bristol who studies iridescence in plants.

This capability is not limited to plants. Insects (jewel beetles and the morpho butterfly are often cited) and fish also have evolved to include structural color as protective or attractive devices, from Luiggi’s article,

The brightest living tissues on the planet are found in fish. Under ideal conditions, for example, the silvery scales of the European sardine and the Atlantic herring can act like near-perfect mirrors—reflecting up to 90 percent of incoming light. It is an irony of nature that these shiniest of structures are not meant to be flaunted, but are intended as camouflage.

“When you’re out in the open water, if you drop down below 10 to 30 meters, in any direction you look, the intensity of light is the same,” explains Nicholas Roberts, a physicist at the University of Bristol who specializes in bio-optics. At that depth, a perfect reflector, or mirror, would seem invisible, because light is equally reflected from all sides and angles.

It will be interesting to see if there’s any future discussion of the giant squid in the context of structural color since, according to very recent research (as per my Feb. 1, 2013 posting), it appears to be covered in gold leaf when observed in its habitat.

Luiggi’s article starts with an ornithologist and circles back in a discussion about the difficulty of creating nanostructures, soft matter condensed physics, and birds,

To create structural colors, organisms must master architecture at the nanoscale—the size of visible-light wavelengths. “But it turns out that biology doesn’t do a good job of creating nanostructures,” Prum says.

Instead, organisms create the initial conditions that allow those nanostructures to grow using self-organizing physical processes. Thus, organisms exploit what’s known as soft condensed matter physics, or “the physics of squishy stuff,” as Prum likes to call it. This relatively new field of physics deals with materials that are right at the boundaries of hard solids, liquids, and gases.

“There’ve been huge advances in this field in the last 30 years which have created rich theories of how structure can arise at the nanoscale,” Prum says. “It has been very applicable to the understanding of how structural colors grow.”

Soft condensed matter physics has been particularly useful in understanding the production of the amorphous nanostructures that imbue the feathers of certain bird species with intensely vibrant hues. The blue color of the male Eastern bluebird (Sialia sialis), for example, is produced by the selective scattering of blue light from a complex nanostructure of b-keratin channels and air pockets in the hairlike branches called feather barbs that give the quill its lift. The size of the air pockets determines the wavelengths that are selectively amplified.

While there’s better understanding of the mechanisms involved in structural color, scientists are a long way from replicating the processes, from the article,

“The three-dimensional nature of the structures themselves is just so complex,” says Vukusic. [physicist Peter Vukusic, a professor of natural photonics at the University of Exeter, UK] “Were it to be a simple periodic system with a regular geometry, you could easily put that into a computer model and run simulations all day. But the problem is that they are never perfectly periodic.”

This article is open access so, as I noted earlier, all you need is the time. As of my Feb. 6, 2013 posting, there was some new research announced about scientists making observations about the structural color in peacock feathers and applying some of those ideas to develop better resolution in e-readers.

Peacocks and their structural colour inspire better resolution in e-readers

Thank goodness birds, insects, and other denizens of the natural world have not taken to filing patents otherwise we’d be having some serious problems in the courts as I have hinted in previous postings including this March 29, 2012 posting titled, Butterflies give and give … .

This time, it’s the peacock which is sharing its intellectual property as per this Feb. 5, 2013 news item on ScienceDaily,

Now, researchers at the University of Michigan have found a way to lock in so-called structural color, which is made with texture rather than chemicals. A paper on the work is published online in the current edition of the Nature journal Scientific Reports.

In a peacock’s mother-of-pearl tail, precisely arranged hairline grooves reflect light of certain wavelengths. That’s why the resulting colors appear different depending on the movement of the animal or the observer. Imitating this system—minus the rainbow effect—has been a leading approach to developing next-generation reflective displays.

The University of Michigan Feb. 5, 2013 news release, which originated the news item, provides information about potential applications and more details about the science,

The new U-M research could lead to advanced color e-books and electronic paper, as well as other color reflective screens that don’t need their own light to be readable. Reflective displays consume much less power than their backlit cousins in laptops, tablet computers, smartphones and TVs. The technology could also enable leaps in data storage and cryptography. Documents could be marked invisibly to prevent counterfeiting.

Led by Jay Guo, professor of electrical engineering and computer science, the researchers harnessed the ability of light to funnel into nanoscale metallic grooves and get trapped inside. With this approach, they found the reflected hues stay true regardless of the viewer’s angle.

“That’s the magic part of the work,” Guo said. “Light is funneled into the nanocavity, whose width is much, much smaller than the wavelength of the light. And that’s how we can achieve color with resolution beyond the diffraction limit. Also counterintuitive is that longer wavelength light gets trapped in narrower grooves.”

The diffraction limit was long thought to be the smallest point you could focus a beam of light to. Others have broken the limit as well, but the U-M team did so with a simpler technique that also produces stable and relatively easy-to-make color, Guo said.

“Each individual groove—much smaller than the light wavelength—is sufficient to do this function. In a sense, only the green light can fit into the nanogroove of a certain size,” Guo said.

The U-M team determined what size slit would catch what color light. Within the framework of the print industry standard cyan, magenta and yellow color model, the team found that at groove depths of 170 nanometers and spacing of 180 nanometers, a slit 40 nanometers wide can trap red light and reflect a cyan color. A slit 60 nanometers wide can trap green and make magenta. And one 90 nanometers wide traps blue and produces yellow. The visible spectrum spans from about 400 nanometers for violet to 700 nanometers for red.

“With this reflective color, you could view the display in sunlight. It’s very similar to color print,” Guo said.

Particularly interesting (for someone who worked in the graphic arts/printing industry as I did) are the base colours being used to create all the other colours,

To make color on white paper, (which is also a reflective surface), printers arrange pixels of cyan, magenta and yellow in such a way that they appear to our eyes as the colors of the spectrum. [emphasis mine] A display that utilized Guo’s approach would work in a similar way.

To demonstrate their device, the researchers etched nanoscale grooves in a plate of glass with the technique commonly used to make integrated circuits, or computer chips. Then they coated the grooved glass plate with a thin layer of silver. When light—which is a combination of electric and magnetic field components—hits the grooved surface, its electric component creates what’s called a polarization charge at the metal slit surface, boosting the local electric field near the slit. That electric field pulls a particular wavelength of light in.

The base colours in printing are CMYK (cyan, magenta, yellow, black). At least, that was the case when I worked in the graphic arts industry and quick search on the web suggests that standard still holds.(Have I missed a refinement?) In any event, here’s an image that demonstrates how this new colour scale can be used,

University of Michigan researchers created the color in these tiny Olympic rings using precisely-sized nanoscale slits in a glass plate coated with silver. Each ring is about 20 microns, smaller than the width of a human hair. They can produce different colors with different widths of the slits. Yellow is produced with slits that are each 90 nanometers wide. The technique takes advantage of a phenomenon called light funneling that can catch and trap particular wavelengths of light, and it could lead to reflective display screens with colors that stay true regardless of the viewer's angle. Image credit: Jay Guo, College of Engineering

University of Michigan researchers created the color in these tiny Olympic rings using precisely-sized nanoscale slits in a glass plate coated with silver. Each ring is about 20 microns, smaller than the width of a human hair. They can produce different colors with different widths of the slits. Yellow is produced with slits that are each 90 nanometers wide. The technique takes advantage of a phenomenon called light funneling that can catch and trap particular wavelengths of light, and it could lead to reflective display screens with colors that stay true regardless of the viewer’s angle. Image credit: Jay Guo, College of Engineering

You can find more about this work in the ScienceDaily news item, which includes a link to the abstract, or in the University of Michigan news release, which includes more images from the scientists.