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Looking at reflectance spectrum of silver, given e.g. here, we can say that more than about $95\%$ of light is reflected by silver. Similarly for white notebook paper, the spectrum is given here, and looks like the paper reflects about $60\%$ of light.

I guess if you put a piece of silver on a paper, you'll see that silver indeed looks darker than paper. My thought is that it's because silver's reflection is specular while paper's one is diffuse, which makes you see something like "average illuminance" color of paper while only color of more or less directly reflected objects in silver surface.

But then it seems somewhat counter-intuitive that if one roughens the surface of silver, it'll be even whiter than paper's surface. Is it actually true? Are there any photos doing such a comparison? Or is my explanation incorrect, and the reason for gray color of silver is another?

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  • $\begingroup$ Good question. I must admit that I've used roughened (shot blasted) metal surfaces in the past, and I recall them looking greyer than paper. Though I suspect shot blasting leaves the metal surface rougher than paper i.e. the size of the scattering surfaces is greater. $\endgroup$ – John Rennie Jul 9 '15 at 7:11
  • $\begingroup$ Could the title usefully be changed to Why does roughened silver look gray while paper white? to make it clear what you are asking? $\endgroup$ – John Rennie Jul 9 '15 at 7:12
  • $\begingroup$ Related: Why are most metals gray/silver? $\endgroup$ – ACuriousMind Jul 9 '15 at 9:54
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The issue may be one of purity at the surface of reflection. Silver oxide is black. The presence of black silver oxide on the surface together with un-oxidized silver may be leading to an overall gray appearance.

The way to test this hypothesis is to prepare a pure sample of silver in an inert atmosphere, and another sample in an oxygen atmosphere, both with the same surface roughness. Then make observations over a period of time.

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