Why Does Wet Paper Allow More Light to Pass Through?

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Wet paper allows more light to pass through than dry paper primarily due to the water smoothing the surface and reducing irregularities, which decreases reflection. This phenomenon is linked to diffuse reflection, where light bounces off microscopic surface features, leading to scattering. When the paper is wet, the refractive index changes, resulting in lower scattering due to the reduced difference between the refractive indices of paper and water. Additionally, using an organic solvent with a matching refractive index can make paper nearly transparent. Overall, the combination of smoother surfaces and altered refractive indices enhances light transmission through wet paper.
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Why does a wet piece of paper let through more light than a dry one?
 
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Most of the change in transparency of paper [and tee shirts] to allow more light thru when wet is probably because the water reduces the surface irregularities by holding them together, flatter, reducing reflection...it makes the surface 'smoother'.


Diffuse reflection - Generally, when light strikes the surface of a (non-metallic and non-glassy) solid material, it bounces off in all directions due to multiple reflections by the microscopic irregularities inside the material ... and by its surface, if it is rough.

More here:
http://en.wikipedia.org/wiki/Translucent#Light_scattering_in_solids
 
Yes. In fact, if you wet it with an organic solvent whose index matches that of the paper, it will become transparent and allow you to read the letter inside an envelope without opening it.
 
vin300 said:
Why does a wet piece of paper let through more light than a dry one?

Because there is reduced scattering, due to the change in relative refractive indices of paper/air vs. paper water. Lower Δn, less scattering.
 
Thanks.That helped.
 

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