Why does an object appear darker when wet?.

[Kuiper83]

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!

 

[Antiphon]

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.

 

[DaveC426913]

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.

 

[Antiphon]

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.

Theres 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.

 

[Andy Resnick]

This question appears periodically here:

https://www.physicsforums.com/showthread.php?t=335919&highlight=darker+wet

 

[mortezat667]

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.