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Visible light Absorption Spectra vs Color of mineral

  1. Jul 30, 2010 #1
    I have been wondering how to realize the color of a mineral by having the absorption Spectra...

    The following case is an example;

    amethyst.gif

    The image is the absorption spectra of a Bolivian Amethyst which looks like this;

    [PLAIN]http://www.tequilabay.com/amethyst300lbbolivian.jpg [Broken]



    I have tried interpreting the purplish color just by reading the spectra, but I wasn't successful... So I will be very thankful for your guidance.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jul 30, 2010 #2

    alxm

    User Avatar
    Science Advisor

    Well all the absorption below 400 nm is UV and so you can ignore that part. You have an absorption peak around 500-600 nm, which is in the green-yellow region.
    The complementary color to green-yellow is purple.
     
  4. Jul 30, 2010 #3
    When light fall on an object, it does 3 things : it gets absorbed, transmitted and reflected.

    Assuming the gems are sufficiently thick, we can assume there is no transmission. That leaves absorption and reflection.

    As you see in your graph, the absorption is minimal around 450 nm, which means there is a reflection peak at around 450 nm. Remember the reflection is what we see.

    Then you use this chart :
    http://en.wikipedia.org/wiki/File:Rendered_Spectrum.png
     
  5. Jul 31, 2010 #4
    This is sure helpful but what about the rest of the absorptions throughout the 450 - 700 nm spectrum?

    How to get the exact tone or wavelength of the color in a quantitative way?

    Thanks in advance :)
     
  6. Aug 1, 2010 #5
    I don't see what you want more. The graph describes the "tone" the only quantitative way it can be described. You can't restrict to a single wavelength. The eye absorbs everything within 450 - 700 nm. The "color" that is perceived includes all the absorbed wavelengths of the graph.
     
  7. Aug 1, 2010 #6
    Basically, the perceived color of a surface includes many wavelengths at varying intensities, just like the perceived taste of a pizza includes flavors of many ingredients in varying intensities.
     
  8. Aug 3, 2010 #7
    You combine this graph with one for the light source. Then integrate the result with "tristimulus values" for human vision.
     
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