What if you could just breathe on something and it changed colour? Researchers at the Technical University Eindhoven in the Netherlands created a material with varying amounts of calcium that changes colour under the influence of moisture!

The Hercules beetle, which served as the inspiration for the research, has a green shield, but when the moisture content changes, it turns black. The researchers aimed to mimic this effect.

The material consists of a low structured polymer, on which varying concentrations of calcium are applied with an inkjet printer. When the material is dry, it only reflects blue light, showing a blue colour, but when the moisture content rises, the polymer expands and shows other colours.

Places with low concentrations of calcium expand a little, creating a green colour, as opposed to places with a lot of calcium. Here, the polymer does not expand at all, giving a blue colour. Parts of the material without any calcium expand the maximum amount, showing the colour orange. By varying the concentrations of calcium nitrate, every visible colour can be created.

The material can be used in many fields, from packaging, cars, decoration, to checking the authenticity of bank notes.

Watch the material change colour in the video below!

Photos: TU Eindhoven