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Thread: Reflections from black surfaces

  1. #1 Reflections from black surfaces 
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    Hello,
    At school we were taught that black surfaces appear black because they do not reflect any light, they absorb all light that falls on them. I have a black polished splash back behind my cooker in which I can see a complete reflection of the room and all the colours in the room. Is there a simple explanation?
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  2. #2  
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    Quote Originally Posted by jonny View Post
    Hello,
    At school we were taught that black surfaces appear black because they do not reflect any light, they absorb all light that falls on them. I have a black polished splash back behind my cooker in which I can see a complete reflection of the room and all the colours in the room. Is there a simple explanation?
    You get reflection from the layer of gloss that sits on TOP of your black screen.
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  3. #3  
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    Thanks for the reply Andrew. This is what I thought but I went to look at other materials (which were showing reflection) such as a black plastic kettle and microwave outer casing. Presumably the material is the same all the way through and has been polished on the surface. So where is the layer of gloss? I ask myself. Yes it is glossy but is the same material as a matt surface. I am still a little perplexed.
    Jonny.
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    Senior Member Strange's Avatar
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    Quote Originally Posted by jonny View Post
    Hello,
    At school we were taught that black surfaces appear black because they do not reflect any light, they absorb all light that falls on them.
    An important point is that they do not absorb all light (*). They may absorb most light but some will be reflected. If the surface is smooth then you will get specular (mirror-like) reflection otherwise you will get a diffuse reflection (just like any other colour material). Diffuse vs specular reflection depends largely on the surface (which is why you can polish dull silver to be shiny, for example).


    (*) A near-perfect black pigment, like Vantablack, will have no reflection and so you will not be able to see any 3D contours - a perfect black sphere will look like a disk.
    https://en.wikipedia.org/wiki/Vantablack
    You can do everything right, strictly according to procedure, on the ocean and it'll still kill you, but if you're a good navigator at least you'll know where you were when you died.
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    You can do everything right, strictly according to procedure, on the ocean and it'll still kill you, but if you're a good navigator at least you'll know where you were when you died.
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  6. #6  
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    Quote Originally Posted by jonny View Post
    is the same material as a matt surface.
    No, it isn't. Polishing re-orients all the elements of the surface in the SAME direction, creating a mirror. In a matte surface, the elements are oriented at random, so, while there MAY BE SOME reflection, it is very minimal. Look up "specular reflection" and "diffuse reflection". Dang! "Strange" ninjad" me!
    One last thing : only IDEAL black body is fully absorbant, REAL black objects do have some reflection.
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  7. #7 Thank you 
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    Quote Originally Posted by AndrewC View Post
    No, it isn't. Polishing re-orients all the elements of the surface in the SAME direction, creating a mirror. In a matte surface, the elements are oriented at random, so, while there MAY BE SOME reflection, it is very minimal. Look up "specular reflection" and "diffuse reflection". Dang! "Strange" ninjad" me!
    One last thing : only IDEAL black body is fully absorbant, REAL black objects do have some reflection.
    Thanks for the links Strange. Vantablack and Claude glass are very interesting and explain a lot. I am happy to accept that the black surfaces around us are not perfect. Oh! and thanks for the reminder about specular and diffuse reflection which I knew about but it was buried somewhere in my ancient brain.
    Andrew, it can't be bad to be "ninjad"by someone who has the same train of thought as yourself. Thanks again.
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  8. #8  
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    Quote Originally Posted by jonny View Post
    Andrew, it can't be bad to be "ninjad"by someone who has the same train of thought as yourself. Thanks again.
    Yep, :-)
    BTW, this was a good thread, jonny
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