Why do things turn dark when wet?

Question

Why do things turn dark when wet?

In: Chemistry

Answer 1

The smooth liquid coating causes the surface to go from rough (microscopically) to smooth (due to the surface tension of the liquid), which changes the way light reflects off the object.

With a rough matte object, incoming light diffuses, or bounces out equally in all directions. But with a shiny object, the reflected light all bounces out in a single, focused direction (assuming you have a single bright light source).

So if an object gets wet, and goes from matte to shiny, the distribution of the light leaving the object becomes less uniform; more of it is now heading in a particular direction (the reflection vector from the main light source), and less of it is now heading in all the other directions. If less light is heading in most directions, then from those directions, the object will appear darker.