Light Bending for Color

When I was thirteen, I wandered into a store that sold a small collection of stones, ranging from agate to snowflake obsidian. Even among the tiger’s eye, something stood out for me — it was an onyx egg. Upon picking it up and rolling it in my hands, I was stunned by the brilliant gold bands on the oblong ends that only appeared when directly looks at. I also have a necklace with a labradorite stone that shines a brilliant blue at certain angles.

What’s going on here?
What I didn’t know at the time I picked up the egg was this is the same optical effect as seen in the oily bubbles that I made throughout my childhood. This phenomenon is called iridescence, derived from the Greek word ‘iris,’ meaning ‘rainbow.’

Aside from soap bubbles and shiny stones, this light bending can be found even in living creatures. A number of butterlies can be seen as completely different colours depending on how their wings are poised. The shells of some creatures, like snails, can be seen as glittering in sunlight. The insides of most all sea creatures possess this, up to, and including, the shells of oysters that make pearls, which of course shine themselves in the same manner. Peacock feathers have iridescent qualities to make predators think their ever-watching “eyes” are on them.

Less specific to colour
The physical principle responsible is refraction, in that the bending of light can actually distort the distance perception we have of the object. A common example is a straw in a glass half full with coloured water. The straw seems fractured right at the line of water, but is still, in fact, whole. It’s the same reason what water and waves can cast such strange light onto walls or faces, and is the principle behind rainbows, whether in air or from light projected through prisms.

Essentially, iridescence is a part of refraction.

Where have you seen iridescence?

Have you experiemented with refraction? With the visible light spectrum?

See if you can make a palette based on what you know or learned of refraction and iridescence, and share it here.

Author: ruecian