What colour is a mirror?

This is also one of those questions which baffled me when I was around 10. Did you know that the human eye can differentiate 10,000,000 million different colours?
But what colour is a mirror?

A mirror (image source: Wikipedia)

You might say Silver because mirrors are often illustrated that way and to be sure they are made out of Silver of silvery things like aluminium. But a mirror in reality is whatever colour you point it at.

In a blue room the mirror is blue.

Reflection of light (image source: Physics World)

And if you look inside a mirror it becomes “You-Coloured.” And object is whatever colour it doesn’t absorb. For example, sticky notes are yellow because when hit with typical white light, they absorb every other wavelength of visible light except for Yellow. Which they defuse into your eyeballs. But a perfect mirror reflects all (Specular and Diffuse Reflection) colour equally, so in a way, you can say that a mirror is White. Except a mirror doesn’t reflects colours in the same way a pigment does. A mirror reflects incoming light in a single out going direction – specular reflection. Not diffuse. This kind of reflection creates an image of the very thing in front of the mirror.

image

Virtual tunnels and green glass: The colors of common mirrors. (image source listed below).

But wait a second. That is a perfect mirror. And we live in the real world where there are no perfect mirrors. Every mirror absorbs a little bit of light. Not enough that it matters – I mean – looks pretty clear to me – but when you take a look at the spectrum of light: reflected by a typical mirror, you will find that it best reflects light within the 510 nanometres range (510 nm).

Which we perceive as Green light. So technically a mirror is a tiny, tiny, tiny bit green. You may have noticed this yourself, when investigating a Mirror Tunnel, this happens when two mirrors face each other. Reflecting the same scene back and forth and back and forth and back and forth with each new reflection way down the tunnel is dimmer and Greener. So maybe real world mirrors aren’t white. They are actually kind of Green.

Blue eyes are not actually blue

Another thing – if you have blue eyes, your eyes aren’t actually blue, in a sense that the molecules inside them are absorbing all of the wavelengths of the visible light and diffusing the Blue. No, no, no, instead, your eyes are blue for the same reason that the sky is blue; interference. In our sky, light encounters molecules of air and because of the size of those molecules, light of longer wavelengths can slip on by. But shorter wavelengths crash into particles, like Blue light and scatter, which is why we see blue when we look at the sky away from the sun. Without air molecules like that, our sky would be just Black. And when direct sunlight has to travel through a lot of air, almost all the colours get scattered out except for the longest wavelengths like the Red. Which is what gives the sunrise and sunset their colour (which I might explain in another post).

The iris of your eyeball contains a hazy layer where light can be scattered just like the sky, through a similar but slightly different process. (Tyndall scattering vs. Rayleigh scattering) shorted wavelengths are scattered more, making your eyes look blue. Unless of course you have some melon in that iris, in which care your eyes are going to be Green, Hazel or Brown. Enjoy those colours.

Resources & References

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2 comments

  1. […] fascinate me, I like writing about colours. Check out my article on the colour of a mirror if you […]

  2. […] fascinate me a lot. Check out my article on the colour of a mirror if you […]

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