Why does an object appear darker when wet?.

  • Context: High School 
  • Thread starter Thread starter Kuiper83
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Discussion Overview

The discussion centers on the phenomenon of why objects appear darker when wet, exploring potential explanations related to light reflection, refraction, and absorption. Participants consider various factors including surface roughness and molecular interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the refractive index of water is responsible for the darker appearance of wet objects.
  • Another participant suggests that the roughness of a dry surface scatters light, while a wet surface reflects light more directly, reducing scattering.
  • A later reply challenges the initial explanation of surface roughness, indicating that increased refraction may play a more significant role than reflection.
  • It is noted that wetting a polished surface does not result in a darker appearance, suggesting that surface texture may not be the sole factor.
  • One participant introduces the idea that molecular interactions between water and the object may create new absorption frequencies, contributing to the darker appearance when wet.

Areas of Agreement / Disagreement

Participants express differing views on the primary reasons for the darker appearance of wet objects, with no consensus reached on the most significant factors involved.

Contextual Notes

Some assumptions about the interaction of light with surfaces and materials are not fully explored, and the discussion includes varying interpretations of the roles of reflection, refraction, and absorption.

Kuiper83
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My Question is just that of the title of the thread;namely, why does something get darker when wet? Does it have to do with the refractive index of water? Or is it something else altogether? Thanks for you help!
 
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The rough dry surface (say a road) scatters light all over because of the roughness. When it's wet the water is a much smoother surface and only reflects light in a much more straight way like a mirror. Your headlights won't scatter back toward you as easily. Same with a piece of rubber or wood.
 
Antiphon said:
The rough dry surface (say a road) scatters light all over because of the roughness. When it's wet the water is a much smoother surface and only reflects light in a much straiter way like a mirror.

That was the answer I started to give (surface roughness). But I checked by Googling. Overwhelmingly, it seems that may not be the answer at all. It seems to be much more about water resulting in a higher amount of refraction rather than reflection.
 
DaveC426913 said:
That was the answer I started to give (surface roughness). But I checked by Googling. Overwhelmingly, it seems that may not be the answer at all. It seems to be much more about water resulting in a higher amount of refraction rather than reflection.

there's some truth to it; water can act a little like an antireflective coating but this is not the main effect. To see this, wet a polished surface like a tumbled stone. It won't get darker. Marble countertop if you have it in the kitchen and it's polished is easy to try.
 
Absorption Frequencies!

I think there is an other reason for this phenomenon. When an object seems blue, it means that the frequencies of oscilations between molecules of that object are different from blue spectrum of light frequency and all other colors absorb except blue. If an object become wet, the forces between water molecules and that object, make new forces and these new forces make new frequencies. So there is more frequencies to absorb by that object and that object will appear darker.
 

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