28 June 2021
Structural colour: More than meets the eye
How microscopic structures create nature’s most dazzling colours.
Ever wondered how the feathers on a peacock or hummingbird achieve their signature glint?
Or why some leaves give off a silvery shimmer, even in low light?
The secret lies in structural colour – an evolutionary process involving microscopic structures that reflect and refract light in unique ways.
Transparent materials are sculpted in patterns invisible to the human eye. These structures work like tiny prisms or holograms (like the security strip on a bank note) to bend and reflect the light back into our eyes.
The result is what we know as 'structural colour'.
Structural colour often appears as the brightest form in nature, characterised by a dazzling metallic sheen. It is 100 per cent reflective, so it can even be seen in the deep sea.
Here are three mesmerising examples of structural colour at work in nature.
Hide and seek
The different layers of an abalone shell capture the evolutionary purpose of colour.
As a marine snail, its shell is made up of many microscopically thin layers to make it strong and robust.
These transparent, thin layers also reflect light and become a form of structural colour.
However, this bright colouring would do more harm than good if it were visible to predators, alerting them to the abalone's presence.
Instead, a dull, pigmented covering (above left) has evolved as a form of camouflage to conceal the naturally brilliant colour beneath (above right).
The silver and blue colours of the Begonia rex ‘Silver Cloud’ result from the selected reflectance of sunlight by microscopic structures in the leaves.
The reflection of rays of all wavelengths in white light produces its silver sheen.
However, too much water in these leaves destroys the structural colour machine.
As a result, the green pigment chlorophyll sometimes dominates what the eye can see.
Hummingbird feathers contain microscopic structures that very precisely reflect sunlight – a natural form of nanotechnology that dates back thousands of years.
A recent study uncovered this insight, revealing the unique structures within the cells that make up hummingbird feathers.
These structures are distinct from other birds as they are shaped like pancakes and contain lots of tiny air bubbles, creating a more complex set of surfaces that allow light to bounce off in different ways.
The result is the majestic gleam that make hummingbirds so recognisable.
Now a new technology, Pure Structural Colour, developed by scientist and artist Andrew Parker, offers an opportunity to recreate these luminous colours on a practical scale for the first time.
As a form of bioinspiration – an innovation inspired by a natural process – Pure Structural Colour represents a unique tool to showcase the relationship between science and beauty in vivid colour.