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I What is this color effect?

  1. Sep 6, 2016 #1
    If I take a standard blue Sharpie pen and write on matte white paper, the ink appears blue as expected, as shown in (a) of the attached photo. If I write with this pen on black plastic, it appears orange (b) in incandescent, fluorescent or daylight illumination and for specular and non-specular viewing angles. How to explain this?

    Another observation - If I use the pen to write on glossy white paper, the ink appears blue for non-specular and pinkish for specular. This is seen in (c) where part of the writing is viewed specularly.

    NiilhQj4lmV1J2-XBdQtWprTqYmM3EiNBBKK2pV38lPfAwnJVp1SFSN782HsCELN9bITY6LurcE1Ew=w1280-h800-no.jpg
     
  2. jcsd
  3. Sep 6, 2016 #2

    Grinkle

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    Thinking about this for the first time, I suppose it has something to do with the light that is reflected by the white surface under the ink. There will be different frequencies reflected off the white surface than the black surface. These different frequencies passing back through the ink will give the ink a different hue to the human eye.

    I don't know what specular means and I am refraining from Google on this question so far.
     
  4. Sep 6, 2016 #3

    A.T.

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  5. Sep 6, 2016 #4

    sophiecentaur

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    I suspect that you are seeing a 'thin film interference' effect which is only seen on a very flat (not matt) surface. This link discusses what I mean. Does it seem familiar to what you have seen?
     
  6. Sep 6, 2016 #5

    A.T.

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    I don't think it's thin film interference, but rather the relation between absorbtion and reflection frequencies described in my link above.
     
  7. Sep 6, 2016 #6
    Then the colors would vary with angle, which they don't (other than the specular/non-specular observation). I quickly browsed through A.T.'s reference and it seems to explain the effect.
     
  8. Sep 6, 2016 #7

    CWatters

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    Does a sharpie pen use pigment ink? In which case the different surfaces probably cause the particles or different types of particles if there is a mixture to be laid down in different ways as it dries.
     
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