Why do some materials appear darker when they are wet?

The difference between your tiles in the hallway and the paving stones lies in the rudeness of the material. The tiles are certainly quite smooth while the paving stones are rough and porous.

If you look now more closely at the surface, you can see that the rough materials have many small holes and rough edges, while the smooth tiles hardly have such irregularities. It is these holes and bumps, that are filled with the wet and become flattened with this. Thereby, they are changing the entire surface of the material and thus also the properties, how the material reflects light.

The light, which is reflected from the respective surfaces can thus be reflected much more varied, when the surface has as many reflecting areas as possible. As the wetness changes the number of reflecting areas, the rough surfaces appear darker when they are wet.

So, it does not lie in your tiles, however, there are also types of tiles, which are made of a rougher material, and therefore change their color with moisture.
2012-07-06 at 18:21