tag:theconversation.com,2011:/us/topics/structural-colour-40971/articlesStructural colour – The Conversation2021-07-26T04:11:04Ztag:theconversation.com,2011:article/1647822021-07-26T04:11:04Z2021-07-26T04:11:04ZHow a bee sees: tiny bumps on flower petals give them their intense colour — and help them survive<figure><img src="https://images.theconversation.com/files/413061/original/file-20210726-5107-125ckdl.jpg?ixlib=rb-1.1.0&rect=48%2C54%2C3977%2C1901&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Scarlett Howard</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The intense colours of flowers have inspired us for centuries. They are celebrated through poems and songs praising the red of roses and <a href="https://theconversation.com/the-mystery-of-the-blue-flower-natures-rare-colour-owes-its-existence-to-bee-vision-153646">blue of violets</a>, and have inspired iconic pieces of art such as Vincent Van Gogh’s sunflowers.</p>
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<img alt="Vase with Three Sunflowers by Vincent Van Gough" src="https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=742&fit=crop&dpr=1 600w, https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=742&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=742&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=932&fit=crop&dpr=1 754w, https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=932&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/412670/original/file-20210722-15-n0fxwg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=932&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Vase with Three Sunflowers by Vincent Van Gogh.</span>
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<p>But flowers did not evolve their colour for our pleasure. They did so to attract pollinators. Therefore, to understand why flowers produce such vibrant colours, we have to consider how pollinators such as bees perceive colour. </p>
<p>When observed under a powerful microscope, most flower petals show a textured surface made up of crests or “bumps”. Our research, published in the <a href="https://pollinationecology.org/index.php/jpe/article/view/606">Journal of Pollination Ecology</a>, shows that these structures have frequently evolved to interact with light, to enhance the colour produced by the pigments under the textured surface.</p>
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<img alt="" src="https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=175&fit=crop&dpr=1 600w, https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=175&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=175&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=220&fit=crop&dpr=1 754w, https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=220&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/412697/original/file-20210722-27-dtm6qp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=220&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">A flower of <em>Tibouchina urvilleana</em> observed under a powerful scanning electron microscope shows a typical bumpy petal surface (left). In comparison, the opposite (abaxial) petal side, rarely seen by an approaching pollinator, shows a less textured surface (right).</span>
<span class="attribution"><span class="source">Author provided</span></span>
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<h2>Sunshiney daze</h2>
<p>Bees such as honeybees and bumblebees can perceive flower colours that are invisible to us — such as those produced by <a href="https://academic.oup.com/aob/advance-article/doi/10.1093/aob/mcab076/6313001">reflected ultraviolet radiation</a>. </p>
<p>Plants must invest in producing reliable and noticeable colours to stand out among other plant species. Flowers that do this have a better chance of being visited by bees and pollinating successfully.</p>
<p>However, one problem with flower colours is sunlight may directly reflect off a petal’s surface. This can potentially reduce the quality of the pigment colour, depending on the viewing angle.</p>
<p>You may have experienced this when looking at a smooth coloured surface on a sunny day, where the intensity of the colour is affected by the direction of light striking the surface. We can solve this problem by changing our viewing position, or by taking the object to a more suitable place. Bees, on the other hand, have to view flowers in the place they bloom.</p>
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<img alt="" src="https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=468&fit=crop&dpr=1 754w, https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=468&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/412673/original/file-20210722-21-1h666q9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=468&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Bumblebee on a smooth blue surface, where the colour is affected by light reflection.</span>
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<p>We were interested in whether this visual problem also existed for bees, and if plants have evolved special tricks to help bees find them more easily.</p>
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Read more:
<a href="https://theconversation.com/our-bee-eye-camera-helps-us-support-bees-grow-food-and-protect-the-environment-110022">Our 'bee-eye camera' helps us support bees, grow food and protect the environment</a>
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<h2>How bees use flower surfaces</h2>
<p>It has been known for some time that flowering plants most often have conical-shaped cell structures within the texture of their <a href="https://doi.org/10.1111/j.1095-8339.1981.tb00129.x">petal surfaces</a>, and that flat petal surfaces are relatively rare. A single plant <a href="https://pubmed.ncbi.nlm.nih.gov/9693152/">gene can manipulate</a> whether a flower has conical-shaped cells within the surface of a petal — but the reason why this evolved has remained unclear. </p>
<p>Past research suggested the conical petal surface acted as a signal to attract pollinators. But experiments with bees have shown this isn’t <a href="https://doi.org/10.1093/cz/zoy096">the case</a>. Other explanations relate to hydrophobicity (the ability to repel water). But again, experiments have revealed this can’t be <a href="https://www.nature.com/articles/s41598-020-67663-6">the only reason</a>.</p>
<p>We investigated how bumblebees use flower surfaces with or without conical petal shapes. Bees are a useful animal for research as they can be trained to collect a reward, and tested to see how they perceive their environment. </p>
<p>Bumblebees can also be housed and tested indoors, where it is easier to precisely mimic a complex flower environment as it might work in nature. </p>
<h2>Flowers cater to a bee’s needs</h2>
<p>Our colleague in Germany, Saskia Wilmsen, first measured the petal surfaces of a large number of plants and identified the most common conical surfaces. </p>
<p>She then selected some relatively smooth petal or leaf surfaces reflecting light from an artificial source as a comparison. Finally, blue casts were made from these samples, and subsequently displayed to free-flying bees. </p>
<p>In the experiment, conducted with bumblebees in Germany, a sugar solution reward could be collected by bees flying to any of the artificial flowers. They had to choose between flying either towards “sunlight” — which could result in light reflections affecting the flower’s coloration — or with the light source behind the bee.</p>
<p>The experiment found when light came from behind the bees, there was no preference for flower type. But for bees flying towards the light, there was a significant preference for choosing the flower with a more “bumpy” conical surface. This bumpy surface served to diffuse the incoming light, improving the colour signal of the flower.</p>
<p>The results indicate flowers most likely evolved bumpy surfaces to minimise light reflections, and maintain the colour saturation and intensity needed to entice pollinators. Humans are probably just lucky beneficiaries of this solution biology has evolved. We also get to see intense flower colours. And for that, we have pollinators to thank.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/plants-use-advertising-like-strategies-to-attract-bees-with-colour-and-scent-92673">Plants use advertising-like strategies to attract bees with colour and scent</a>
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<p class="fine-print"><em><span>Adrian Dyer receives funding from The Australian Research Council.</span></em></p><p class="fine-print"><em><span>Jair Garcia does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Bees can perceive flower colours and hues which are invisible to us — such as those produced by reflected ultraviolet radiation.Adrian Dyer, Associate Professor, RMIT UniversityJair Garcia, Research fellow, RMIT UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1364112020-04-16T09:28:27Z2020-04-16T09:28:27ZHow did insects get their colours? Crystal-covered beetle discovery sheds light<figure><img src="https://images.theconversation.com/files/328419/original/file-20200416-192698-1282qkf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of the weevil.</span> <span class="attribution"><span class="source">University College Cork</span></span></figcaption></figure><p>The natural world is full of colour, and few groups of animals are as colourful as insects. From the dramatic black and yellow stripes of wasps and striking spots of ladybirds to the dazzling metallic sheen of jewel beetles, insects show a kaleidoscopic array of hues, patterns and optical effects.</p>
<p>But exactly why insects are so colourful isn’t always clear. How and when did insects evolve colours, and have their roles always been the same? We recently discovered some spectacularly preserved blue-green colours in the scales of 13,000-year-old fossilised weevil beetles. Our find, <a href="https://royalsocietypublishing.org/doi/10.1098/rsbl.2020.0063">published in Biology Letters</a>, sheds light on the evolution of the most complex colour-producing structures known in insects: 3D biophotonic crystals.</p>
<p>Until now, we had only ever found one example of such preserved crystals in a fossil. Our new specimen supports the idea that 3D colour-producing structures may have evolved as a means of camouflage rather than to attract attention. But more importantly, the discovery indicates that these fossils may be much more common than we previously thought. This opens up greater potential for us to learn far more about the evolution of these “structural colours”, and the biophotonic crystals that produce them.</p>
<p>These futuristic-sounding structures are part of a family of materials that often have a regular, self-repeating architecture at a nanoscopic level. <a href="https://www.nature.com/articles/nature01941">Such structures</a> are often able to scatter specific wavelengths of light, producing so-called structural colours that have particular optical properties. We encounter these every day: the rainbow sheen on a DVD, the swirling colours of a soap bubble, and the fire-like flash in a crystal of labradorite or opal.</p>
<p>The structural colours produced by biological nanostructures are the brightest and most intense in nature. Classic examples include the dazzling blue flash of a <a href="https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2002.2019?casa_token=cG8wI56dg9UAAAAA:_HCj8AAEShnB4i_Syn7AL3dxRaZ6J0Rr2koCfMxR2-RTFCyic3TPpR9IjM9eVfrFwn8LbZio_cKudg"><em>Morpho</em> butterfly’s wing</a> and the golden mirror-like reflection from a <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsif.2017.0129"><em>Chrysina</em> beetle</a>, both produced by microscopic layers in the insects’ tissues. </p>
<p>These structures produce flashy colours that you can only see from a narrow range of viewing angles and that change depending on viewing angle (a phenomenon known as iridescence). These optical effects, and the associated vivid colours, happen to be very useful for startling predators and attracting mates.</p>
<p>But there are also <a href="https://www.nature.com/articles/nature01941">3D biophotonic crystal structures</a> that can manipulate light in all directions. In insects, these are found only in the scales of weevils, longhorn beetles, butterflies and moths, where they can form intricate arrays of chitin (the material that makes up the bulk of the exoskeleton of insects) and air.</p>
<p>Studying where these structures have appeared throughout evolutionary history could help us understand why they appeared in the first place. The problem is that the fossil record of 3D biophotonic crystals is virtually non-existent. There is only one known example, <a href="https://royalsocietypublishing.org/doi/10.1098/rsif.2014.0736">a 735,000-year-old fossilised beetle</a> found by one of us (Maria) in 2014 in rock made from layers of sediment deposited by a glacier in Canada. </p>
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<img alt="" src="https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=235&fit=crop&dpr=1 600w, https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=235&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=235&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=295&fit=crop&dpr=1 754w, https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=295&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/328300/original/file-20200416-140735-1n50keu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=295&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The crystals were identified with a microscope and electron microscope.</span>
<span class="attribution"><span class="source">University College Cork</span></span>
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<p>Our new discovery provides another fossilised example of 3D biophotonic crystals from a different type of location, suggesting their preservation is probably more widespread than previously thought. The specimens are 13,000-year-old weevils found by our colleague <a href="https://theconversation.com/profiles/scott-armstrong-elias-118184">Scott Elias</a> (formerly of Royal Holloway University), in sediments from the ancient lake of Lobsigensee in Switzerland. </p>
<p>The newly-discovered insects appear rather underwhelming, preserved as small brown fragments of wing cases. But at high magnification, the scales’ colours are astonishing: vivid greens, blues and hints of yellow. We examined the scales using powerful electron microscopes, which confirmed the presence of ordered nanostructured arrays. Preservation of this level of tissue nanostructure is mind-boggling, even for us hardened professionals.</p>
<p>With our microscope studies, we had good evidence that the structures were 3D biophotonic crystals, but to prove it required structural diagnoses and optical modelling. This was done by our colleague Vinod Saranathan, who examined the scales using X-ray analysis at the Argonne particle accelerator near Chicago. Saranathan’s work confirmed that the fossil scales contain a single diamond photonic crystal nanostructure. And so the brilliant green, yellow and blue colours are indeed fossilised structural colours.</p>
<p>However, the colours from the individual microscopic crystals appear to mix at a visible level, suppressing iridescence and producing an overall greenish colour. The result is a matt rather than a shiny colour, unlike that of most insects with 3D nanostructures. This suggests the weevil’s crystals evolved as a form of camouflage, matching it to its leafy background habitat. </p>
<h2>Where are the other fossils?</h2>
<p>But if the fossilisation of 3D biophotonic crystals is more common than we thought, why haven’t we found more specimens? Maria’s <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/41/4/487/131196/The-fossil-record-of-insect-color-illuminated-by?redirectedFrom=fulltext">previous research</a> confirmed the crystals should survive the rigours of decay and burial during fossilisation. Instead, the poor fossil record of these structures probably reflects the fact that the scales likely fall off after death. </p>
<p>What’s more, scales bearing structural colours are usually less than 100 microns across, effectively invisible to the naked eye. So it’s likely that many other examples of fossilised 3D crystals have actually been overlooked, due to the small size of insect scales.</p>
<p>What now? Clearly we need to search deeper in time for more examples. Good targets include fossils from the Cenozoic Era (from 66 million years ago to today) that preserve <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2011.1677">other types of structural colour</a>, and insects hosted in amber, which can preserve scales with <a href="https://advances.sciencemag.org/content/4/4/e1700988">evidence of colour</a>. </p>
<p>Most useful of all would be studies of the earliest weevils, from the Late Jurassic and Early Cretaceous periods (163-100 million years ago). These would allow us to test whether the evolution of 3D biophotonic crystals was linked with the proliferation of flowering plants that took place at this time. Close examination of the insect fossil record will likely reveal many more examples, helping us understand the environmental and ecological factors driving evolution of these incredibly complex tissue structures and their functions.</p><img src="https://counter.theconversation.com/content/136411/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maria McNamara receives funding from the European Research Council via Starting Grant ERC-2014-StG-637691-ANICOLEVO.</span></em></p><p class="fine-print"><em><span>Luke McDonald is supported by European Research Council Starter Grant ERC-2014-StG-637691-ANICOLEVO awarded to Maria McNamara. </span></em></p>Researchers realised a dull-looking 13,000-year-old weevil was actually covered in brilliant green, blue and yellow nanoscopic crystals.Maria McNamara, Senior Lecturer in Geology, University College CorkLuke McDonald, Postdoctoral Researcher, School of Biological, Earth and Environmental Sciences, University College CorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/808972017-07-20T20:14:26Z2017-07-20T20:14:26ZExplainer: how scientists invent new colours<figure><img src="https://images.theconversation.com/files/178939/original/file-20170720-23989-7gdktm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Butterfly wings, like those of the monarch butterfly, have inspired scientists to create "structural colours".</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/macro-close-monarch-butterfly-wing-192477281?src=f5fwSTXGv_vApXd0_p0Xtg-1-20">tea maeklong/Shutterstock</a></span></figcaption></figure><p>For <a href="https://theconversation.com/buried-tools-and-pigments-tell-a-new-history-of-humans-in-australia-for-65-000-years-81021?">tens of thousands of years</a>, humans have created colours through simple chemistry. At first we used dyes found in nature such as berries and charcoal. Later, new pigments were synthesised in the lab.</p>
<p>By now, you might think scientists would have come up with every possible colour, but in fact they continue to be invented to meet new challenges: tanks need better camouflage, mirrors need to be brighter, and satellites need new light-absorbing finishes to be able to peer further into space.</p>
<p>Today researchers use physics to invent new colours, inspired perhaps by the iridescent shades <a href="https://www.nature.com/articles/srep16637">created by structures</a> in butterfly wings that scatter light.</p>
<p>These new structural colours are the result of an interaction between light and nanoscale features many times thinner than human hair. </p>
<p>Inventing colours is now an exciting combination of chemistry along with new materials and structures.</p>
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<figcaption><span class="caption">Blue butterfly wing structural colour demonstration.</span></figcaption>
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<h2>The story of Vantablack</h2>
<p>Vantablack is a famous example of colour created through structure.</p>
<p>Scientists at Surrey NanoSystems in the UK launched “<a href="https://www.surreynanosystems.com/vantablack/science-of-vantablack">Vantablack</a>” <a href="https://www.surreynanosystems.com/media/news/sensitive-electro-optical-imaging-and-target-acquisition-systems-launch-at-farnborough-international-air-show">in 2014</a>. Made from packed vertically aligned tiny carbon tubes, the structure and arrangement of the tubes further enhances the natural black nature of carbon, letting <a href="https://www.surreynanosystems.com/vantablack/faqs">it trap 99.96%</a> of light.</p>
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<figcaption><span class="caption">A sphere coated in Vantablack.</span></figcaption>
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<p>To put this in perspective, if you think of a forest of trees about a metre in diameter, then these trees would scale to be around one kilometre high. Light falling on this very tall forest of tubes bounces around and is almost perfectly absorbed. </p>
<p>Several research groups <a href="https://www.nasa.gov/topics/technology/features/new-nano.html">including NASA</a> have focused on similar efforts to achieve the “blackest black”. While several materials can be used for this purpose, including gold nano-particles and rods, it seems <a href="http://www.nature.com/nnano/journal/v11/n1/full/nnano.2015.228.html">carbon nanotube coatings</a> are the most efficient option.</p>
<p>Although not as absorbing of light, nature has its own version of Vantablack. The <a href="http://www.nature.com/articles/srep01846">West African Gabon viper’s</a> dorsal scales, some of the darkest found in the wild, have a specific “leaf-like” structure. It uses its black structural colour as part of an elaborate camouflage adapted to its forest habitat.</p>
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<img alt="" src="https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178936/original/file-20170720-23989-1fljfnt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The West African Gabon viper’s dorsal scales are some of the darkest found in nature.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/bitis-gabonica-gaboon-viper-on-white-595262093?src=gMT3GS8Lx3EE7eb5d7zmNg-1-2">mat.hak/Shutterstock</a></span>
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<h2>Why do we need the “blackest black”?</h2>
<p>The pursuit of an absolute black material has been driven by a need to completely absorb light energy and convert it to heat.</p>
<p>The sensitivity of optical instruments requiring a minimal amount of stray or unwanted light, such as telescopes, could be greatly improved with the addition of Vantablack-coated surfaces in their optical system, for example. This could enable the observation of fainter stars. </p>
<p>In infra-red or thermal sensor systems, its use could also improve the signal-to-noise ratio and result in better resolution in heat detection. Since materials like Vantablack absorb almost all light, other possible applications could lie in thermal collection systems such as solar panels.</p>
<p>The coating is relatively fragile, however, and typically needs to be protected or encased within an instrument.</p>
<h2>Perception and reflection</h2>
<p>We see colours because light is reflected off our surroundings. It is quite disturbing to look at a Vantablack surface, after all, as the lack of light reflection gives a sensation of emptiness that is hard for the brain to process.</p>
<p>Whist Vantablack absorbs light, in some applications, such as mirrors, we want them to reflect all possible light.</p>
<p>Mirrors for concentrated solar applications need highly reflective coatings to reflect all the light and concentrate the Sun’s energy to a single point to create heat. That heat can then be used to generate electricity. </p>
<p>We are also developing <a href="https://www.australiaunlimited.com/technology/colinhall">visual effects</a> for automotive use by embedding microparticles in coatings, creating a satin or low-gloss plastic trim. These microparticles are made of glass and scatter the incoming light, bouncing around the layer they are embedded in and giving rise to a uniform satin effect. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178937/original/file-20170720-24017-1vterhu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The scales of the European sardine also use reflective structural colour.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/european-pilchard-sardina-pilchardus-market-istanbul-654168997?src=sKtFfxnZT1fBjP5a7NRGZQ-1-70">Alexandra Tyukavina/Shutterstock</a></span>
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<p>Traditionally, this would have been done with electroplating, a process where metals are deposited onto a surface from liquid metal salt baths. This alternative technique avoids the <a href="https://www.ncbi.nlm.nih.gov/pubmed/21919030">cancerous materials</a> used in electroplating to deliver similar performance but with few environmental problems. </p>
<p>New colours can also be achieved by layering materials of different refractive index – a measure of the ability of a material to bend light. When you stack a number of layers with different refractive indices on top of each other and control their thickness, you can produce interference. This is the same phenomenon as when you see an oil slick on water. </p>
<p>But, as usual, nature has got there first. <a href="https://www.nature.com/nature/journal/v490/n7421/full/490449a.html">Reflective structural colour</a> can be found on the scales of <em>Sardina pilchardus</em>, otherwise known as the humble European sardine.</p><img src="https://counter.theconversation.com/content/80897/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Colin Hall has received funding from Excelerate Australia through the AA2020CRC and from SMR Automotive . He is affiliated with Materials Australia. </span></em></p><p class="fine-print"><em><span>Eric Charrault received funding from Excellerate Australia through the AA2020CRC.</span></em></p>Scientists continue to invent new colours for new applications thanks to nanoscale structures.Colin Hall, Research Scientist in decorative and hard coatings, University of South AustraliaEric Charrault, Research Fellow in Energy and Advanced Manufacturing, University of South AustraliaLicensed as Creative Commons – attribution, no derivatives.