A colour that never fades

The Pollia condensata plant.

The Pollia condensata plant.

Scientists have found nature’s way of creating colour that never fades, a technique they say could replace pigments used in industry with natural plant extracts in products from food colouring to security features in banknotes.

It is 10 times more intense and bright than any colour achieved with a pigment

Layers of cellulose that reflect specific wavelengths of light – structural colour found in peacock feathers, scarab beetles and butterflies – make a particularly intense blue in the Pollia condensata plant, scientists say.

Samples of the fruit in plant collections dating back to the 19th century had not lost any shine or intensity.

“By taking inspiration from nature, it is possible to obtain smart multifunctional materials using sustainable routes with abundant and cheap materials like cellulose,” said University of Cambridge physicist Silvia Vignolini.

“It is 10 times more intense and bright than any colour achieved with a pigment,” said Dr Vignolini, who led the study with plant scientist Beverley Glover.

Although the fruit has no nutritional value, birds were attracted by its bright colour, possibly as a decoration for their nests or to impress mates, helping in seed dispersal.

“This obscure little plant has hit on a fantastic way of making an irresistible, shiny, sparkly, multi-coloured, iridescent signal to every bird in the vicinity, without wasting any of its precious photosynthetic reserves on bird food,” said Dr Glover.

And, unlike pigments, structural colour does not fade over time as it is not broken down by absorbing light.

“Edible, cellulose-based nanostructures with structural colour can be used as substitutes for toxic dyes and colorants in food,” said Dr Vignolini.

“The paper industry is already set up to extract and use cellulose and its processes could also be adapted for security labelling or cosmetics. Cellulose-based structures have a really strong optical response and are completely inert in the human body,” she said.

Another advantage of the technique is that the desired colour can be achieved by adding layers in the structure to reflect different wavelengths.

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