The converse of this question is perhaps "why are metals shiny". From what I understand, metals are covered by a sea of free electrons that oscillate in response to incident light/EM wave, and the oscillation is in turn associated with another EM wave travelling in the opposite direction from the first one. Hence the reflected light back to our eyes. (correct me if I am wrong. Also I am not too clear on the precise mechanisms of EM waves. For example, how does the electric field in incoming wave cause the electrons to move if there are no charged particles in the wave? This may be a self-explanatory question in that electric fields by definition affect charges, but how? I know this is a really basic concept, but I've never been able to get it. How is the oscillation of electrons associated with the new wave, what determines its direction? Does this oscillation use up some sort of energy, if so, where from?)
So with non-metals, in which electrons are fixed in place, is the dull appearance because of the lesser extent to which the electrons can oscillate? How does this relate to the intensity of the reflected light (maybe because of the smaller amplitude of the reflected wave?) Or, does the reflection occur via a completely different mechanism?
The other aspect is absorption. Then the question becomes, what is the difference between metals and non-metals that make the rate of absorption different, if the dullness is due to the greater absorption of light by materials such as cloth etc. ? What is meant by absorb more light anyway, which quantity does 'more' correspond to apart from the bright/dim perceived by our eyes?
There are so many questions here but any help is greatly appreciated!