[neilep (OP)]

Why Do Wet Clothes Look Darker Once Wet ?







whajafink ?




Sheepy
 xxxx

[Eternal Student]

Hi.

   I don't know and am not an expert,  however I don't think that all clothes do look darker when wet.   Anyone who's worn the wrong pair of shorts into a swimming pool will know that some clothes can go very see-through rather than darker.

    I suspect a lot of it depends on the diffraction and refraction of light in the space between the clothes fibres because that is very likely to change when you swap the medium in those spaces from air to water.

    Consider a butterfly from the genus "Morpho",  it appears to have blue wings.   However, they only appear that way in air.   Most of the colour is just a consequence of diffraction and refraction occurring in small spaces or pockets in the wings where there are also thin fibrous structures called "lamellae".   You get very dramatic shifts in colour when you put the wings into different liquids because the spaces or pockets between these fibres will then have a very different refractive index.

   Here's a video from YouTube that shows how those wings will change colour in different liquids, if you have 5 minutes to spare and would like to see some pictures.

   I suspect clothes with their fine fibres and space between those fibres is essentially exhibiting the same effects.   So maybe clothes that did go darker in water might actually turn lighter or take on a whole new shade and tone when immersed in liquid nitrogen.   I hope that makes some sense.

Best Wishes.

[neilep (OP)]

Hi.

   I don't know and am not an expert,  however I don't think that all clothes do look darker when wet.   Anyone who's worn the wrong pair of shorts into a swimming pool will know that some clothes can go very see-through rather than darker.

    I suspect a lot of it depends on the diffraction and refraction of light in the space between the clothes fibres because that is very likely to change when you swap the medium in those spaces from air to water.

    Consider a butterfly from the genus "Morpho",  it appears to have blue wings.   However, they only appear that way in air.   Most of the colour is just a consequence of diffraction and refraction occurring in small spaces or pockets in the wings where there are also thin fibrous structures called "lamellae".   You get very dramatic shifts in colour when you put the wings into different liquids because the spaces or pockets between these fibres will then have a very different refractive index.

   Here's a video from YouTube that shows how those wings will change colour in different liquids, if you have 5 minutes to spare and would like to see some pictures.

   I suspect clothes with their fine fibres and space between those fibres is essentially exhibiting the same effects.   So maybe clothes that did go darker in water might actually turn lighter or take on a whole new shade and tone when immersed in liquid nitrogen.   I hope that makes some sense.

Best Wishes.

Thank Ewe ES,

 I found the analogy to the Morpho butterfly's wings really helpful. Your hypothesis about the role of diffraction and refraction is fascinating. Thanks for sharing your insights and the video !

[Petrochemicals]

Pretty much everything that I can think of when it has absorbed water goes darker when wet, soil, sand, masonry, wood

[neilep (OP)]

Pretty much everything that I can think of when it has absorbed water goes darker when wet, soil, sand, masonry, wood

That's a fascinating observation! Most materials do indeed appear darker when they're wet, don't they? I think it's because the water fills in the tiny pores and spaces on the surface of the material, reducing the amount of light that's scattered and giving the appearance of a darker colour. It's a clever point you've made, and it's true for a wide range of materials, from soil and sand to masonry and wood.

[Petrochemicals]

My guess was going to be wet materials are cooler as the water naturally wishes to be a gas, thus absorbing energy from the light, given unlimited energy all water desires to be gaseous in atmospheric earth conditions,  it is only humidity that stops it all evaporating away.

[Bored chemist]

Very few clothes get their colour from diffraction effects- essentially only iridescent ones.

The real reason why most clothes look darker is essentially that same as the reason that white swimwear is a risky option.
Water acts as an index matching fluid and reduces the amount of reflection at the surface of the cloth fibres. That lets the light penetrate further and so it gets more opportunity to interact with the dyes.

https://en.wikipedia.org/wiki/Index-matching_material

[Petrochemicals]

From T'internet.


"Furthermore, the weave of the fibers creates many layers of reflecting surfaces. Therefore, the portion of the light that successfully makes it through the first fiber without being reflected can still be reflected by the lower layers "

 "It's the scattering and absorption of light that make the object appear darker. It's a physics phenomenon called total internal reflection "

"Being wet means that there's a water film covering the material, mediating the change in refractive index, resulting in reduced reflection "

"Water fills in the microscopic gaps and irregularities on the material's surface, reducing the amount of light that is scattered or reflected back to the observer,  "

But really I think the real answer is this Neil,

" Clothes and fabrics appear darker when they're wet because less light is reflected back at the observer from the material"

[Bored chemist]

For those of you who were wondering what Petro's tag line
"For reasons of repetitive antagonism, this user is currently not responding to messages from;
BoredChemist"
means, I kept pointing out that he was wrong.

The colour change isn't due to total internal reflection.
That happens to light inside a "dense" medium - like the fibre- trying to get out rather than light outside the fibre trying to get in (where it will encounter they dye)

[neilep (OP)]

Thank you all for your continued responses👍👍👍👍