Why Do Things Get Darker When Wet?

Have you ever noticed that when you used a tissue paper to clean up water, the color of the tissue paper turned dark when it is wet? Or have you noticed that your shirt turn darker when you are soaked in a rain? In this article, we will explore the science behind this particular situation.

When your shirt is soaked, a layer of water sits on top of the fibers. This re-refracts the light that’s bouncing off the fibres back onto the fibres, instead of a normal single refraction when the material is dry. This allows the material to absorb more light, making it appear darker.

A shirt doesn’t really change color when it is wet

When you zoom into your shirt, you will notice that there are many tiny broken pieces of thread sticking out. Each of these catch and refract light, making the fabric appear a bit lighter. This is also part of the reason why clothes ‘lose color’ in the wash as more threads break, and wear begins to become more noticeable. When you apply water, these non-uniform fibers get pressed down or are completely glossed over. This means the fibers are no longer able to refract and diffuse light to the degree they were doing so beforehand. This makes them appear darker. It hasn’t actually changed colors, it’s simply unable to reflect as much light overall through the water as it could without the water.

The thin film of water acts as a slightly mirrored surface. This cause more complex interactions between incident light and the object. But does this mean that a wet object will get hotter as it absorbs more light?

Well, there’s a gap of latent heat between the increase of temperature of water and its change of state. At this gap, the water will continue absorbing heat. Eventually, it vaporizes but the surface of the object will also be siphoning heat from the water. Hence, it won’t prevent the object from warming up. It’ll actually increase the rate of energy transfer to the object because water is highly conductive.

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