What happens to the atomic structure that makes a blob of pure metal, or an alloy, that characteristic metal sheen?
Is it at all similar to other sheens found in nature, such as bluejay feathers or shellac?
All those poorly-bound electrons!
Agree… what you’re seeing is electrons. 
No. Photons are reflecting off the object and hitting the retina. The retina sends a message to the brain on the spectrum and content of what is being seen and the brain invents an image. An apple is not red, the brain interprets the light coming off the apple as red. Red is an interpretation. As is “luster” which I presume means shine, as in lots of light waves across the spectrum being reflected.
This is mostly false. Red color corresponds to an objectively measurable wavelength of photons, it’s not just "an interpretation.
And beowulf is right, the loosely bound electrons is the reason for the metallic sheen effect. See here for a cool experiment http://youtu.be/tYjQXjUUvwY
I disagree. What I posted is scientific fact. You see the green or the red because the object absorbs the other colors in the spectrum and rejects the color you see. Neil DeGrasse Tyson agrees with my point of view. 50 Awesome Quotes by Neil deGrasse Tyson » TwistedSifter see tweet 12. He explained this more at length in the recent Cosmos series.
It is quite a mind bender the first time through, but after being taught this from an early age by my father, a high school physics teacher, I have heard it repeated in dozens of science lectures, textbooks and TV science shows. Your apple is anything but red.
That would seem to be a reasonable definition of what it means to be green or red.
This is a distinction without a difference. There is no difference between saying that an apple is red and saying that the light that reflects from it mostly consists of red photons. That’s what color is. And the fact that your brain interprets red photons as red doesn’t mean the apple isn’t red - it’s just how your visual system detects color.
As for Neil DeGrasse Tyson, I looked through the list of quotes you linked to, and the closest thing I could find was:
Note that he doesn’t say that green plants aren’t actually green.
As for why metals are lustrous, as others here have already pointed out, it’s because metals have a lot of electrons that aren’t tightly bound to particular atoms or molecules. A photon that hits a free electron is a lot more likely to be reflected than a photon that hits a bound electron. I think this is because a bound electron has only a few energy states it can be in, while a free electron isn’t so restricted.
Free electrons give metals some of their other properties, as well: electrical conductivity, heat conductivity and malleability.
None of the posts above actual answers the OP’s question, nor even purports to.
Taking the loosely-bound electrons answer and running with it: Then what happens? What is it about loosely bound electrons that makes metals shiny? I don’t believe that you’re actually seeing electrons, as Crafter_Man kinda-sorta said.
For a partial answer (that I think I know, physics student flunkie that I am) I think it’s something like this: Photons coming from the sun or a light bulb strike the object. Electrons absorb the photons, and get all het up. Electrons then get un-het up, and lose the energy that they gained, giving off a photon.
Now, there is controversy over whether the photon thus released is the same photon that the electron previously absorbed, or whether it’s a new photon. (Whatever. Quantum physics is weird.) In any case, the photons thus released will be a characteristic color, and when those photons blow into your retina (hetting up still more electrons there), the rest happens as The Second Stone wants us to believe (a process that involves up-hetting of whole bunches of electrons along the nerve pathways in your brain).
I think.
If any of the above is correct, can we now address the OP’s questions?
[ol][li] Given this process, and the notion that the loosely bound electrons of metals have something to do with it all, why are metals shiny?[/li][li] Is it the same process in play for shiny non-metallic things too?[/ol][/li]
(ETA: Okay, partially simulposted with Jeff Lichtman above, who actually took some steps towards answering the OP.)
I don’t think anything happens to the atomic structure to make a metal sparkly-wharkly, rather we can scrape off the oxides that form on the surface of the metal.
If you do the same thing with a non-metallic element like carbon you won’t get the same result. Also, many metals (like chromium) are shiny even with an oxide layer.
One thing I know is that when the metal surface is rough, then those newly emitted photons come off at all angles because a random photon might hit the surface at any angle, while a very smooth surface will have a more or less well defined direction it faces.
Can anyone explain why a high enamel surface is shiny while a matte surface isn’t. No metals involved here, AFAIK.
Near as I can tell from these answers, a metal’s luster is not related to the actual lust inherent in the metal itself. So, there’s no scientific link between jewelry and romance.
The perception of color isn’t just that a particular wavelength is “red” because we see it as red, the fact is that many distinctly different wavelengths can be perceived as red and this fact was clearly demonstrated by Edwin Land in his “Mondrian” experiments that were part of his work in color constancy. Your brain decides what color something is based on both information from the retina and on how it relates to the total visual field.
The fact that color optical illusions exist is proof that color is a decision.
The oxides of carbon don’t typically remain on the surface they form on, and the oxide layer on chromium is shorter than a wavelength of light.
The question is what change in atomic structure of metal gives the shiny-whiney look. Seems it’s not a change in this structure that provides the look, rather it’s due to more “macro” conditions, like being flat and not rough, not having a thick layer of rust or not actually having light available to reflect.
Take 40 grit sandpaper to enamel for long enough, it won’t be whiney-shiny anymore. But that’s not a change to the atomic structure of the enamel, it still has “loose” electrons in it’s outer orbitals.
Yes.
Colour can be objective… Just capture the rainbow on a chart, and then compare the test colour to the chart, in the same lighting conditions.
If you think that colour is purely subjective, All I can say is that, “Good luck at traffic lights” .
Diamonds sparkle because they reflect… Thats the interface between air and the dense material…
Mica is shiny and yet has no metal in it,but I think it is reasonable dense.
One thing about the electron structure is that it allows the substance to become DENSE…
Also the number of free electrons means the electrons can be at many energy levels… and move to many energy levels. Bound electrons have specific energies and hence specific frequencies… so that you can say that bound electrons give specific colour… (lustre is not a colour, black is not a colour… ) … So it will get confusing… the lustre of metals may be because of the lack of colour giving electrons… those that have the specific frequency…
If an object reflects only or mostly red wavelengths, isn’t that the quintessence of what it means to be red?
Not as such, as far as minerals go - it’s in the normal range for common rock-forming minerals, much less dense than metallic minerals.
Mica is “shiny” (it’s not the same “shiny” as metallic lustre, it’s mostly “pearly” or “silky” lustre, depending) because it has many thin layers (same kind of lustre as mother-of-pearl, but not quite the same because of differences in the layer structures) not because it is dense or because it has free electrons (it is, in fact, a very good insulator)