How does grey occur in elemental materials such as metals? I believe that grey arises from the simultaneous reflection and absorption of all colors of the spectrum (in different atoms of course), as mixing opposite colors on the spectrum would do. How would this occur in a one-element material? How does this occur on an atomic level?
$\begingroup$ The color of any material is highly dependent on its surface. A piece of metal can look dull grey when its covered with fine scratches or it can have a mirror polish. The difference is not a material property but depends on the geometry of the scattering surface. $\endgroup$– CuriousOneDec 29, 2014 at 3:08
$\begingroup$ Possible duplicates: physics.stackexchange.com/q/72368/2451 and links therein. $\endgroup$– Qmechanic ♦Dec 29, 2014 at 7:03
A clean un-oxidized metal surface is not usually grey but rather reflective like a mirror. In fact, mirrors are constructed by coating a sheet of glass with a thin layer of metal atoms. The grey color of a slightly oxidized surface, which includes almost metal surfaces you encounter in daily life, look grey because some of the ambient white light is absorbed.
How would this occur in a one-element material? How does this occur on an atomic level?
Metals have relatively mobile electrons. Therefore, when an electromagnetic wave comes in, the electrons can move around easily under the influence of that wave's electric field. That means that an incoming wave causes the electrons to oscillate at the same frequency as the wave itself. Therefore, the electrons in the metal surface emit radiation at exactly the same frequency as the incoming wave. In other words, the light is reflected at the same color as it had before.