Iridescent Sheet with Oily Film

This spectacular piece of transparent plastic shimmers between metallic pastel shades as you move it around, shifting between pale blue, green, gold and pink as it reflects the light. The film is made up of multiple, very thin layers of transparent plastic, and this layering is the key to how the iridescence works: the spectrum of colours change with constructive interference from the multiple reflections from the multiple layers. The beams of light bounce around from the upper and lower layers, and from the upper and lower surfaces of the films all interacting, splitting the white light into its constituent colours, which change in relation to the movement of the material, and the angle you view it from (constructive interference).

Iridescence is often seen in nature in the wings of beetles and flies, the feathers of starlings and hummingbirds and the inside of a shell – the colours too are often formed this way and called structural colour to distinguish them from pigment-based colours. A different kind of iridescence is also seen in thin films of naturally derived, petroleum-based substances, like spilt diesel, crude oil floating on water, or soap bubbles. All of these have only one layer, but are constantly swirling with colours due to the changing thickness of the film.