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I'm an A-level student and I love learning new things in physics. A new concept that I learnt says that the reflection is due to the scattering of light by electrons in the material. I've got my head around this yet something that bothers me is how do shiny surfaces like a mirror or reflective surface like silver or platnum reflect almost all of the light that it receives and yet certain other metals don't. If it depends on the electrons scattering light, why is the material or composition of electrons so important? What is the property that makes reflective surfaces the way that they are even when the number of electrons differs?

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  • $\begingroup$ Could you make the title more descriptive? I'd answer the question, "Why do shiny surfaces reflect more light than other surfaces" with, "because that's how shiny is defined". $\endgroup$
    – user12029
    Apr 8, 2016 at 18:25

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A clean metallic surface appears shiny because it is reflecting light. The interaction is due to the conductivity of the surface of the metal.

When surface conditions change, the reflectivity is reduced. For example, a clean aluminum surface is very reflective, and aluminum coatings are used on the back side of mirrors; the glass protects the clean aluminum surface.

If the clean aluminum surface is exposed to air it will rapidly oxidize. You can test this by scratching or cutting any thick piece of dull aluminum. The oxidized layer is actually a good insulator, but is quite thin. The same holds for most other metals. If they don't tarnish, then stuff gets on the surface.

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  • $\begingroup$ is it possible that in addition to the conductivity of the the metal surface that the glass and the internal reflection between its two surfaces also plays a part in smoothing out the image? $\endgroup$
    – Bill Alsept
    Apr 8, 2016 at 16:11
  • $\begingroup$ @Bill Alsept: glass is a dielectric reflector, so back-and-forth reflections are possible, but are suppressed if the surfaces are optically contacted. The front glass surface of a back-coated glass mirror will also reflect, but only about 4%. If you look closely, using a finely detailed object, you should be able to see a clear double reflection. $\endgroup$
    – Peter Diehr
    Apr 9, 2016 at 1:56

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