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It's commonly stated that metals are lustrous, or shiny. To my understanding, "shiny" here is a result of specular reflection. If we posit that metals have flat, pristine surfaces, then the reflection will be specular. This preserves the relation between light rays incident to the surface, as this answer explains. To understand why metals are shiny, we'd need to relate a property of metals (say the presence of conduction electrons) to flat surfaces that give rise to specular reflection. My question is, how do we make this jump i.e. how do the properties of electrons give rise to flat, pristine surfaces that allow a material to be lustrous?

Edit: With the help of John Rennie, I have narrowed the question down. This answer explains why metals are good reflectors. Now, all that is left to make is an argument for why metals have flat surfaces. Then, I can combine this information to say that the linked answer explains why metals are ideal reflectors. This allows the light to make its way to the surface. Then, the flat surface ensures there is no further perturbation to destroy the reflection.

So the question becomes why do metals have flat surfaces?

Relativisticcucumber
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1 Answers1

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Whether a reflection is specular or not depends on the roughness of the surface. If the variations on the surface are much smaller than the wavelength of the incident beam, the reflection will be specular and vice versa.

This has nothing to do with the optical properties of the material at hand. The contribution of metals in that regard is their high reflectivity which says nothing about the direction of light but simply how much they intensity they reflect as opposed to how much they absorb.

High reflectivity together with the usually (relatively) smooth surfaces of metals give them their unique appearance.

B. Shpigel
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