New Technique Reveals How Butterfly Wings Grow into Natural Diffraction Gratings

Iridescence and holography are two techniques used in security printing to display colour shifting phenomena that depend on the angle of viewing or illumination of a surface. Colour shifting phenomena also occur naturally in nature, such as the iridescent shimmer of a butterfly’s wings due to the precise structure and arrangement of the microscopic scales on its wings (see HN August 2021).

The iridescence on butterfly wings does not occur from pigment molecules but by how the butterfly wing is structured into what physicists call photonic crystals. A butterfly wing's shimmering qualities materialise when a molecule called ‘chitin’ forms scales arranged like roof tiles. The arrangement acts like a diffraction grating, splitting light into several beams in different directions – dependent on their colour.