Why do clothes darken when wet?

Clothes and fabrics become darker when wet because less light is reflected from the matter towards the user.

Have you ever had water spilled on your lap right before a big meeting? Or have you ever felt your armpits start to sweat in the middle of a date that was going well?

In both of these cases and many more, you’ll find fabrics and clothes tend to darken when they’re wet. It would be nice if humidity didn’t discolor our clothes to such a noticeable extent, but it’s an inevitable part of life. The question is, why do things get so dark when wet?

Why do clothes darken when wet?
Clothing is made up of many layers of microfibers, creating a lot of surface for light to reflect.

Before learning about the nuance change of material colors in the presence of moisture , we need to know how we perceive color. When light from the sun enters the Earth’s atmosphere and illuminates a field of grass, we see that the grass is green because the light energy is only partially absorbed.

The grass will absorb the blue, red, yellow, and orange light wavelengths in the electromagnetic spectrum, and it will reflect the green light wavelengths (560-520nm). Thus, the light that bounces off the grass enters our eyes, where it contacts the cone cells in the retina, and is interpreted as green grass.

Everything we see follows the same mechanism; the wide range of colors we perceive in the world, from the colors of plants to the colors of the clothes and products we buy, all depend entirely on how light is absorbed or reflected by those objects.

Besides, textures and material composition can affect the way we see colors. For example, a piece of clothing is made up of many layers of microfibers, creating lots of surfaces for light to reflect off.

Even though a material may be partially transparent, many layers of fabric and numerous individual fibers still reflect color towards the viewer. For example, a white t-shirt is composed of fibers that are almost transparent, but in large quantities and densely packed, they create a bright white color. The interaction of fabric, light, and air creates a uniform color for the human eye.

In addition, the fabric may look smooth, but all the fibers that make up a cloth create a rough surface on a microscopic level. Rough surfaces often look brighter than smooth ones, because the light hitting it has more angle to bounce back , creating more reflections, and making objects appear brighter. Smooth surfaces like metal or glass often reflect light in a single direction based on the angle of the light entering it.

Why do clothes darken when wet?
A wet cloth will be darker than a dry one, but it is also likely to become more “shiny”.

Now that you understand how light interacts with a dry surface, continue to study how things change when a matter or surface gets wet. The key point here is that, when an object gets wet, the water on its surface acts as a second reflective surface.

Take a bright red t-shirt as an example. When light hits a dry t-shirt, all wavelengths of light will be absorbed, except red wavelengths (700-635nm) which will bounce back to our eyes. If the t-shirt is wet, when light hits the fabric, it will penetrate the water above. The water has now filled in all the gaps between the fibers that were previously filled with air. As a result, the path of light that bounces back to our eyes will be bent by the water. This condition is known as “complete internal reflection” , where light is reabsorbed by water instead of bouncing back to the human eye.

If the number of photons from the fabric bouncing back to your eye becomes less, the matter will appear to have a “darker” color. The amount of light reflected back by matter remains the same, but only a fraction of it reaches your eye. As mentioned above, a smooth surface will reflect light in a different way than a rough surface . Adding water to a rough surface of the fabric will essentially make the surface smoother. Depending on your viewing angle relative to the wet surface and the light hitting it, you may see a small, bright reflected light. A wet cloth will be darker than a dry one, but it is also likely to become more “shiny”.

As the fabric dries, air will gradually return to the gaps between the fibers, allowing light to bounce back and reflect more freely, rather than being absorbed or re-reflected by water on the material.

The interaction of light with the physical world and the structure of our eyes is really interesting research, revolving around such factors as viewing angle, optics, light, and perception versus reality. . As far as the color of the fabric is concerned under dry and wet conditions, the material actually does not change color when wet, but its reflectivity has been changed, making the appearance of the material appear dark. before the eyes of the observer.