How would I go about illustrating iridescent scales and feathers?
Ruth Geal, England
Allison replies
The key to painting iridescence lies in understanding a little about how iridescence works and how it appears in nature. Iridescence is a product of structural coloration. It’s produced by microscopic structures that refract light waves between layers of light-reflecting cells. The location and shape of these structures varies from species to species – lizards, snakes, and birds, for instance, are all different.
Birds use iridescence for courtship and display. When painting feathers, I put down a base tone and then begin laying out saturation changes and where the light will hit. I tend to think of it in terms of hot spots (saturated warm tones where the light hits) and cool spots (darker, cooler saturated spots that help boost the hot spots), that I then fade into slightly desaturated midtones where the shape falls out of the light.
A snake’s iridescence is tied heavily to the kind of scales it has. Those with heavily keeled scales are often dull and drab, while those with smooth scales (ideal for friction reduction) exhibit it quite frequently. Once I’ve plotted out scales and have an idea of where the light will hit I start building up low-opacity colour in the spots where the iridescence should fall (this is typically not where the light directly falls, but on either side of it). Understanding the variety and functionality of the scales will help you determine what kind of scales your creature should have, and how much iridescence would make sense.