Why do clothes darken when wet?

Clothes and fabrics become darker when wet because there is less light reflected from the material toward the user.

Have you ever had water on your thighs before a big meeting? Or have you ever felt your armpits begin to sweat in the middle of a good date?

In both cases and many more, you'll find that fabrics and clothing tend to darken when they're wet. How good it would be if moisture did not discolor our clothing to such a noticeable level, but it was an inevitable part of life. The question is, why do things become darker when wet?

The way we see colors

Clothes are made up of many layers of small fibers, creating lots of surfaces for light to be reflected.

Before we learn about the changing shades of physical colors in the presence of moisture , we need to know how we perceive colors. When light from the sun enters the atmosphere of the Earth and illuminates a meadow, we find that the grass is green because the light energy is only partially absorbed.

The grass will absorb blue, red, yellow, and orange light wavelengths in the electromagnetic spectrum, and it will reflect the wavelengths of green light (560-520nm). So the light bouncing off of the grass gets into our eyes, where it comes in contact with the cones in the retina, and is interpreted as green grass.

Everything we see follows the same mechanism; The range of colors we see in the world, from the color of trees to the colors of the clothes and products we buy, all depends 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 small fibers, creating lots of surfaces for light to be reflected.

Even though a material may be partially transparent, many layers of individual fibers and countless separate threads still reflect the color towards the viewer. For example, a white T-shirt is made up of almost transparent fabrics, but in large quantities and dense density, they create a bright white color. The interaction of cloth, light, and air creates a uniform color for the eye of the viewer.

In addition, the fabric may look smooth, but all the fibers that make up a cloth create a rugged surface at the microscopic level.Rough surfaces often look brighter than smooth surfaces, because the light that comes in will have more angles to bounce off , create more reflections, and make us see lighter objects. Smooth surfaces like metal or glass often reflect the light in a single direction based on the angle of light coming in.

When the fabric is wet

A wet cloth will be darker than a dry cloth, but it is also likely to become more "glossy".

Now that you understand how light interacts with a dry surface, continue to study how things change when a material or surface gets wet. The bottom line here is that, when a material is wet, the surface layer of water acts as a second reflective surface.

Take a bright red T-shirt as an example. When light shines on a dry T-shirt, all wavelengths of light will be absorbed, except for the red wavelengths (700-635nm) that will bounce back our eyes. If the T-shirt gets wet, when light shines on the fabric, it will penetrate the top layer of water. The water now fills every gap between the fibers that were once filled with air. As a result, the path of light that bounces off our eyes will be bent by the water. This condition is called "complete internal reflection" , or light, instead of being reflected back into the eye of the viewer, reabsorbed by water.

If the amount of photons from the cloth bounces back to your eyes becomes less, the material will look like "darker". The amount of light reflected by matter remains the same, but only a fraction of that reaches your eyes. As mentioned above, a smooth surface will reflect light in a different way than a rough surface . Adding water to the fabric's rough surface will basically make the surface smoother. Depending on your viewing angle relative to the wet surface and the light coming in, you may see a small, reflected stream of light. A wet cloth will be darker than a dry cloth, but it is also likely to become more "glossy".

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

Conclusion

The interaction of light with the physical world and the structure of our eyes is really an interesting study, focusing on factors such as perspective, optics, light, and perception compared to reality. . In the case of the color of fabrics under dry and wet conditions, the material does not actually change color when wet, but its reflective ability has been altered, making the appearance of the material look dark. than before the eyes of the observer.

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