Iridescence means shiny with many colours. Many animals have iridescent colours.

Iridescence is structural colour from refracted light (crystals), diffraction gratings (feathers or butterfly wings), thin film (oily surfaces), multiple layer interference (nacre in shells), or 3-D arrays of spheres (opals).

The word iridescence comes from iris, the Greek word for rainbow. An iridescent object has many tones of colour. Iridescence creates colour by splitting and reflecting light from different structures – which is why it is often called structural colour.

Iridescence occurs in soap bubbles. Iridescence can also be found in the sky and in the earth. Clouds reflect and refract sunlight, and rainbows transform the sky after rain, but can also be seen in the steam of kitchen kettles or within ice crystals.

In animals, iridescence occurs, for example, in peacock feathers, bird of paradise feathers, abalone (paua) shells, beetles and beetle wings, scales from a python, and pearl oyster shells.

Feathers and butterfly wings have diffracted light, which means that the light bends as it encounters a tiny obstacle or opening. This creates a distinctive pattern in troughs and crests that reflect different shades of the same colour, and it looks like the colour is flashing or moving. Rapid flashes of colour can be achieved even with small movements.

Animals use iridescence to communicate. Iridescent patterns on an animal often confuse predators, which enables an animal to escape. Iridescence is also used to attract a mate. For example, a male bird flutters their iridescent wings to attract a female.

Sometimes iridescence is used to communicate social status. For example, male monkeys that are more dominant in a social group have deeper blue iridescent skin.

Iridescence is a beautiful and remarkable colour in the animal kingdom.

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM