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A White object reflects all the visible colored light but so does a flat silver object (mirror) so what makes them look so different?

This has been answered here but that shouldn't be true because white objects can be highly polished too. Also if we make a silver object irregular/rough it doesn't turn white

EDIT:

enter image description here enter image description here

(1st img) The metal surface doesn't particularly look white (as the answer claims in the above link). (2nd img) The white surface does reflects impressions of windows here but it look nothing like a mirror (in terms of showing the natural vibrant colors of the object in front of it as a mirror does). Why the difference in nature if they do almost the same thing (i.e. reflect all the colored light. Or are we missing something?

44yu5h
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  • Could you provide some examples of polished white surfaces which are not reflective, and rough silver surfaces that do not turn white? That might make it clearer whether you are talking about reflectivity or color. – Codename 47 Apr 26 '23 at 13:20
  • @Codename47 Thanks for replying. I've added the images. I'm talking of the appearance in general. Why does the mirror looks so natural but not a white surface if they do something very similar (reflect light) – 44yu5h Apr 26 '23 at 13:50
  • @SolomonSlow Yes i partly agree but if you look at the other side of the coin.. howsoever the texture of the metal is it doesn't look like white (it poorly reflects the reflection of objects in front of it) – 44yu5h Apr 26 '23 at 14:32
  • Oops! Deleted my previous comment. Thought maybe it wasn't really pertinent to your question. Sorry. – Solomon Slow Apr 26 '23 at 14:33
  • @StevanV.Saban Thanks for replying. I don't think that's what happens. Because as it is stated "white reflects all the visible light" and so does a polished metal. Except if there is some other component of light we are missing? – 44yu5h Apr 26 '23 at 14:52
  • I checked the spectral reflectance curves for white paints and you are correct so I'm deleting my answer. – Stevan V. Saban Apr 26 '23 at 15:23
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    As an apology I offer this: https://engineering.mit.edu/engage/ask-an-engineer/why-doesnt-a-plain-white-piece-of-paper-reflect-light-but-a-mirror-does/#:~:text=White%20surfaces%20are%20composed%20of,combination%20as%20the%20color%20white. – Stevan V. Saban Apr 26 '23 at 15:32

1 Answers1

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The answer in your link is correct. But you are too.

The mirror like reflection is called specular. There are degrees of smoothness. A smoother surface will have a larger specular component to its reflection. You can see this if you polish a metal surface with finer and finer grits of sandpaper. You get a mirror with 600 grit.

The two white tiles above are both smooth, but one is smoother.

A metal surface often turn grey. This is because it absorbs some of the light, more or less equally at all wavelengths. The specular reflection keeps the color of the incoming light but is dimmer. The non-specular reflection is also dimmer. If you dim a white light, it looks grey and then fades to black.

So why don't both components look grey. They would under the right circumstances. The specular component is brighter than the non-specular component, and so looks whiter. A lot of color perception happens in your eye and can work in unexpected ways. See What is Gray, from a physics POV?.

Some metals, such as copper and gold, do not absorb uniformly across the visible spectrum. They make excellent mirrors at longer wavelengths. But they do color the reflected light by absorbing shorter wavelengths.

mmesser314
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  • (+1) That's a pretty convincing theory. But I will wait for some more answers because i think it's more deeper than this. – 44yu5h Apr 26 '23 at 14:53
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    @44yu5h Regarding the two tiles - the reflective one on the right could also have a thin coating of a mostly transparent reflective material (think clear paint (like a car clear coat), or a thin glossy film) that creates a faint mirror-like reflection, while the rest of the light that passes through gets diffusely reflected from the undersurface. The metal surface in your image has directionality to it's roughness - that is, it's anisotropic, which is why you get these bright and dark bands (it stretches the reflected image perpendicular to the streaks). – Filip Milovanović Apr 29 '23 at 12:41
  • @44yu5h BTW, the answer you linked to in your question doesn't explain as much why an object is white, but rather why an object that is white (or any other color, for that matter) doesn't appear mirror-like. It's because of diffuse reflection (light being scattered in all directions) - this could be caused by microscopic irregularities of the surface itself, or by other mechanisms like subsurface scattering, or a combination of both: see this Wikipedia article. – Filip Milovanović Apr 29 '23 at 12:53
  • @FilipMilovanović YES! you are exactly right. The mirror like appearance could be because of the transparent coating. It is in fact the case is almost every white thing. I couldn't find anything white which reflects except for enamel of teeth and opal stone (not completely reflective yet perceptible enough) So I'm confused.. does it matter if it is an element or molecule or as you stated anisotropic (opal stone)? I want to believe that it is what you and others are saying but something in me says there's more – 44yu5h Apr 29 '23 at 13:21
  • @FilipMilovanović Yes your argument about the diffused light is correct but I'm countering it with the fact that silver things don't turn white when their surface get rough. What if there's another component of light we are missing? Because as mysterious as light is.. surety is far – 44yu5h Apr 29 '23 at 13:24
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    Thin film coatings can definitely affect reflectivity. They are used for mirror coatings, antireflection coatings, and much more. But to make a mirror, you have to have a smooth substrate, and the thickness of the coating has to be carefully controlled. For more information, see Dielectric Coatings – mmesser314 Apr 29 '23 at 14:03
  • @44yu5h Objects that aren't already reflecting all visible spectrum frequencies about equally aren't going to turn white as the surface becomes rougher. They'll loose their mirror like reflection, as the reflected image will become more and more blurry, until you can't tell there's a "reflection" anymore. Sliver might turn white-ish if you were able to make very tiny random (not streak-like) imperfections on the surface (much finer than the finest sandpaper). Imagine those white & gray bands being circular instead, and blending together as they become blurrier. 1/2 – Filip Milovanović Apr 29 '23 at 14:47
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    @44yu5h But you're right that in general there's more to it when it comes to how this diffuse scattering in all directions comes about - most of the time (depending on the material) it happens because of internal structure beneath the surface (subsurface scattering). Read the "Mechanism" section in the Wikipedia article I liked to, it discusses exactly what you want to know. 2/2 – Filip Milovanović Apr 29 '23 at 14:47
  • @FilipMilovanović Sure! Thanks! I will be looking deeper into this in future. I will hit you up if I find anything relevant :) – 44yu5h Apr 29 '23 at 15:29