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While frying some chicken I was wondering why the fat becomes transparent when melting. As far as I know, transparency is caused by the fact that the substance can't absorb photons of visible light (due to band gap or other excitation mechanisms)

Is this the reason for liquid/solid fat as well? How does the fat lose excitation possibilities when molten?

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  • $\begingroup$ Due to the change in refractive index $\endgroup$
    – QuIcKmAtHs
    Dec 29, 2017 at 13:25
  • $\begingroup$ Can you elaborate on that? Does solid fat have a refractive Index? An imaginary one? Why Does the Index change? $\endgroup$
    – Jasper
    Dec 29, 2017 at 13:44
  • $\begingroup$ The opaque-ness of an object is due to its ratio of scattered and absorbed light. Solid oil has a high refractive index. Very very high. Liquid oil, on the other hand, is commonly used in ancient times to apply on papers to make it more transparent, and possibly were used as windows. reddit.com/r/askscience/comments/ztktx/… $\endgroup$
    – QuIcKmAtHs
    Dec 29, 2017 at 13:48
  • $\begingroup$ I am commenting right now as I think it is too short for an answer. However, should it be upvoted by you or gain sufficient upvotes, I can post it as an answer $\endgroup$
    – QuIcKmAtHs
    Dec 29, 2017 at 13:49

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The same phenomenon occurs with ice/ water, butter, Coconut Oil etc.

Let's look at butter.

While it is a liquid, it is yellow in color. This means that it is reflecting and transmitting only yellow light. When it turns into solid, it still appears yellow, but in this case, it does not transmit any light, it just reflects it.

This is because when the butter is solidified, certain small crystals ( Crystallites ) are formed which absorb all colors except yellow ( as expected ) and they reflect all the yellow light back ( because their refractive index becomes very high as explained by XcoderX in the comments ).

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  • $\begingroup$ Can the new absorption features of the crystallites be explained by new excitation possibilities, i.e. the photon energy is distributed over the whole crystallite? $\endgroup$
    – Jasper
    Dec 30, 2017 at 18:37
  • $\begingroup$ I don't think that there should be a change in the excitation energy of the atom, well because butter atoms remain butter atoms whether you cool butter or heat it! There is a change in the refractive index of the substance not due to the change in the properties of the constituent atoms, but due to the new arrangement of the atoms. $\endgroup$ Dec 31, 2017 at 15:43

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