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This is a followup question on 'Why shadow of light that goes through colored glass becomes colored?'

The way I understand answer given is: more light from other color spectra than that of color (lets say red) of the material (lets say glass) is being absorbed so more of red gets through and gets reflected (less of other spectra gets through and gets reflected) this is why glass looks transparent red and so does shadow.

Can there be a case where colored transparent material reflects one color but lets through some other (which would make shadow to be of different color than that of glass)?

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  • $\begingroup$ I don't know about the case for glass, but gold is green by transmitted light: you can make gold leaf thin enough that this experiment is fairly easy to do. $\endgroup$
    – user107153
    Sep 13, 2016 at 8:58
  • $\begingroup$ @tfb gold isn't really transparent in a 'normal' sense (like a glass), however I understand point you are making - reflects one absorbs other. Thanks. $\endgroup$ Sep 13, 2016 at 9:01

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Yes There is. These kinds of filters are called interference filters, They reflect one or more parts of the spectrum/transmit the rest parts and they do not absorb light at all. For example consider this interference filter which transmits green light and reflects blue and red parts of visible light:

enter image description here

Red light and blue light is perceived by our brain as pink and so it looks pink, It transmits green light so it will have a "shadow" which is green.

Now consider this filter which lets in red and blue parts of visible light and reflects green part.

enter image description here

Now this filter has a pink "shadow" because it transmits red light and blue light which is perceived by our brain as pink, and it reflects green light so it looks green.

Filters are made out of normal glass, but they have optical coatings on them which are very thin and these coatings are what reflect some frequencies of light and transmit others. These optical coatings are made of metal like aluminium. What part of visible light is reflected is dependent on the metal you use for coating.

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  • $\begingroup$ Hi Kosta, thanks for the answer, do you by any chance know what material these filters are made of? Or they are using cuts in surface to let higher frequencies to go through while lower ones hit the cuts and get reflected Thanks. $\endgroup$ Sep 13, 2016 at 15:40
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    $\begingroup$ They are made out of normal glass but they have optical coatings on them which are very thin and these coatings are which reflect light and transmit others. These optical coatings are made of metal like aluminium. What part of visible light is reflected is dependent on the metal you use for coating. $\endgroup$ Sep 13, 2016 at 15:49
  • $\begingroup$ Moreover, you could also have non-complement reflection and transmission if the glass absorbed some of non-reflected wavelengths (assuming the interference filter is on the light source side). $\endgroup$
    – Ruslan
    Nov 26, 2016 at 18:18
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No. I think it can not because; The color of the glass comes from the fact that the glass absorbs all six colors in white light except for the color you see (the color of the glass). If the glass is blue, it absorbs all colors but not the blue color - the blue keeps traveling to your eyes, or into its "shadow".

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  • $\begingroup$ Hi Vukani, welcome to SE.Physics, as much as I appreciate you answering I expected to get answer like there cannot be material that wouldn't let through light without reflecting it because: ....... Your current answer pretty much repeats what has been said in previous question... Sorry. $\endgroup$ Sep 13, 2016 at 11:24

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