Why do some materials appear darker when wet?

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In summary, the conversation discusses the phenomenon of certain materials appearing lighter when wet. The link provided explains that this is due to the increased scattering and reflection of light on wet surfaces, causing more light to be absorbed. The conversation then speculates on why some materials, such as wood and the speaker's trousers, exhibit this property. It is suggested that the mechanism may be similar to the effect of polishing on wood, where a change in surface roughness affects light reflection.
  • #1
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I say 'some materials' because it is not true for all. Usually, clothes appear darker when wetted, but I have one pair of trousers that actually goes ligher when water spashes on them, so it is not 'always'.
 
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If you are very interested you can read this http://www.victoria.ac.nz/scps/staff/pdf/darkerwhenwet.pdf" which mathematically models the reflection of light for wet objects. The general idea is that when an object is wet, light is scattered and reflected more leading to an increased tendency for the reflecting object to absorb light instead.
 
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  • #3
OK, as far as it goes (thanks for the link). So why do some materials look lighter when wet?
 
  • #4
Which materials in specific do you have in mind?
 
  • #5
I don't know what my trousers are made of. It says its a synthetic/natural fibre mix. But are my trousers really the only material known that displays this property?
 
  • #6
I'm guessing this is similar to when white T-Shirts and paper turn translucent when wet. Outside of this transparency I really cannot think of any clothing which becomes lighter when wet. (Although admittedly I haven't paid too close attention to wet clothes :uhh:)
 
  • #7
Some materials (I'm thinking of wood specifically) also get darker when polished as opposed to rough but I have no idea whether or not it's due to the same mechanism.

It MAY be closely related, because the mechanism in wood is that rough wood had a HUGELY larger surface area (due to little troughs and grooves) and thus reflects more light. Polishing reduces the surface area. Maybe wetting "smooths out" the surface area in a similar way.

If that's the case, it is possible that your special pants may be of a slick material that actually gains a surface roughness when moisture raises the fibers, thus it reflects more light.
 

1. Why do some materials appear darker when wet?

When materials get wet, the light that hits them is scattered in different directions. This causes the material to appear darker because less light is being reflected back to our eyes. This phenomenon is known as "wetting transparency".

2. Is it because the water is changing the color of the material?

No, the water itself is not changing the color of the material. The change in appearance is due to the way light interacts with the wet surface. The color of the material remains the same, but the way we perceive it is affected by the wetness.

3. Why does this effect only happen with certain materials?

Some materials have a smoother surface, which allows light to reflect off of it more evenly. When these materials get wet, the light is still able to reflect off of them, making them appear less dark. However, materials with rougher surfaces scatter light more, making them appear darker when wet.

4. Does the thickness of the water layer make a difference in how dark the material appears?

Yes, the thickness of the water layer can affect how dark the material appears when wet. Thicker water layers will absorb more light, making the material appear darker. Thinner water layers may not have as much of an impact on the material's appearance.

5. Is this effect only visible in natural light?

No, this effect is visible in any type of light, including artificial light. However, certain lighting conditions may make the effect more or less noticeable. For example, a bright light source may make the wet material appear less dark, while a dim light source may make it appear darker.

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