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Why are ice cubes grey in the middle?

  1. Mar 6, 2012 #1
    Do you see how the ice-cube is less transparent in the center in this image?

    http://p.lefux.com/61/20091013/A10470000C/Crystal-LED-Ice-Cube-1-Gallay.jpg [Broken]

    This image doesn't capture exactly what I see in my cup but it gets my point across. Why is an ice cube less transparent in the center? I'm guess it's because the atoms are more tight bonded in the center. But if that's true then

    1. why does that make them less transparent?
    2. why are they more tightly bonded in the first place?

    I put this question in general physics because it doesn't seem to deal with any one area of physics except maybe classical physics.
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Mar 6, 2012 #2

    sophiecentaur

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    Good question.
    The outside freezes much faster than the inside and, the longer the freezing process, the larger the crystals that form. Also, any gas that comes out of the water near the outside will end up as bubbles near the centre, along with ice crystals.
    So we have large crystals and possible bubbles in the middle.
    Light gets internally reflected when it goes through a (nominally) transparent material if there are changes in refractive index. Light will be scattered and take a longer path on its way through this central part. It will be attenuated and images, seen through it will be diffused, giving a grey appearance..
     
  4. Mar 6, 2012 #3
    Thanks for the explanation, I feel more knowledgeable in this forum..:smile::smile::smile: thanks,,,
     
  5. Mar 6, 2012 #4

    sophiecentaur

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    It's just like a 'grey' cloud. Less light gets through.
     
  6. Mar 6, 2012 #5
    good question but even better answer. thanks for the help.
     
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