• Question: What colour is a mirror?

    Asked by 13marbles to Adam, Chris, Eleanor, Jessamyn, Sinead on 10 Nov 2013.
    • Photo: Adam Murphy

      Adam Murphy answered on 10 Nov 2013:

      Hey. I really like this question. Your head tries to tell you two things at once and you have to figure out the right one!

      Colour is how our brain processes all the bits of light that come into our eyes. When light hits, say a tomato, some of the light is absorbed and only the red light is reflected into our eyes, so the tomato is red!

      Really high quality mirrors, like in the Hubble telescope are made from really pure silver, made to reflect every single bit of light that hits them.

      So as to what colour they are, the way I like to think is that they don’t have a colour of their own. They’re like a little TV screen that’s always on, only showing the colours of the things you can see through them.

      Thanks so much for the question!

    • Photo: Christian Wirtz

      Christian Wirtz answered on 10 Nov 2013:

      This is a nice question!

      One could think of it in such a way as to ask what colour the starting material that makes up your mirror has. In that case you would probably end up with “gray-ish” as most mirrors are made of glass with a silver backside.

      But you weren’t asking for the colour of the mirror material, you wanted to know the colour of the mirror. By definition (there are several, but Wikipedia actually gave the most relevant one), a mirror is “an object that reflects light in a way that preserves much of its original quality” which means that an ideal mirror will not change the reflected light at all. “Not changing it” also means that it cannot add another colour, which it would if it had one itself. Therefore we’ll have to conclude that a (ideal) mirror, by definition, has no colour.

    • Photo: Sinead Cullen

      Sinead Cullen answered on 11 Nov 2013:

      Hey,
      Wow cool question, very clever!
      A mirror might look silver because it’s usually made look that way in books or movies. But it’s actually the color of whatever is reflected onto it.Mirrors were originally created by placing a transparent, greenish glass over a reflective silver backing, which is still usually visible at the edges. This is why mirrors are often thought to be silver.

      However, strictly speaking a mirror has no colour at all. Colours are created by the light that bounces off an object – if it looks red, that’s because red is the main colour not being absorbed.

      A mirror is designed to reflect everything and, with no colours absorbed at all it has no colour of its own.

      Hope this helps!

    • Photo: Eleanor Holmes

      Eleanor Holmes answered on 11 Nov 2013:

      A true mirror is the colour of whatever is reflected in it.

      This question has already been answered so perfectly by everyone else. Here are some more things to think about colour.

      All colour is reflections of light interpreted by the rods and cones in our eyes. There is a firmer grounding for colour in physics in that different wavelengths (which can be measured by instruments without “seeing” the colour) are representative of different colours – red is about 700 nanometers (nano!) and blue is about 400 nm. But what we see when we see a red or blue object is all the interpretation of our brains and the the wavelengths that are being scattered instead of absorbed by the object.

      Here’s an interesting experiment: Get a torch and cover the top with some transparent, coloured cellophane (like a sweet wrapper). Turn off all the other lights and shine your coloured light on some coloured pencils or crayons. Do they all really look like the colours you are used to?

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