You see it on a soap bubble, on oil spills, sometimes it is seen on metallic surfaces. Also it is used for coating glasses and much more. The idea is that there is a really thin layer on top of material that interfers the light and make colored reflection, as its thickness is comparable to the wavelength of light.
Let’s start with a simple metallic ball. Make a new scene, add a sphere and assign silver material to it:
Then open “Silver” material in the material editor, open its layer and locate the “Specular” option there. Check Thin-Film interference box to activate the effect:
Here’s what you see below:
So basically you need to configure the index of refraction of the film and then adjust its thickness to get the apperance you want. Let’s change our material and set N to 1.5:
That looks better, right? Now let’s change the thickness of the film to 250:
Then change it to 300:
Here’s how to make it green:
As you see, you can make absolutely any color or gradient by playing with Thickness and N parameters. The next time you render colored sunglasses - just use this effect.
Now let’s make it even more interesting. We’ll need a texture like this:
Load it to Thickness slot and see what happens to the ball:
Owlet uses minimal thickness (100) for black parts of the texture and maximal thickness (100 + 400 = 500) for its white parts. You can provide noise, gradient or ornament maps to get the coating you need.