Why do certain white cloths become translucent when wet?

[Engywook]

Inspired by the thread about why wet stuff seems darker than dry stuff…

Exhibit A: Men’s white cotton undershirt, dry. A poor transmitter of light.

Exhibit B: Men’s white cotton undershirt, wet. A better transmitter of light, such that when worn by…

you get the picture. Why, though?

[voltaire]

I’m not gonna touch the part about how light acts when it travels through water, but it defintely has a lot to do with how the wet Tshirt clings to the body more than the dry one.

I don’t think a wet Tshirt held away from the body (like a dry one would be) is any more translucent than a dry one.

Mmmmmmm, clingy wet Tshirts!

[Duke_of_Rat]

Well, it wouldn’t be very fun going to a dry tee shirt contest…or if a wet tee shirt was the same opacity as a dry tee shirt it would sure cut back on the entertainment factor.

Some things are just the way they are, and we are not to question why.

[Popup]

Come on, Duke of Rat, that’s the wrong attitude. We’re here to fight ignorance, not wallow in it. On to Wet T-shirts:

Now, this is a very interresting questions, that brings us close to the very essence of life. Boobs. No, sorry, I meant physics. There is a very good explanation for this, and CalMecham answered it brilliantly a couple of years ago, in the thread Wet T-Shirts (sheesh, people can’t search nowadays.)
Anyway, what he said was:

The secret to it all is index matching. Both the cotton fibers that make up a white T-shirt (assuming it’s uncolored) and the air are pretty transparent. The T-shirt appears white because you get reflection and scattering at each cotton/air interface. You can minimize this effect if you were to wet the cotton down with some liquid that has the same index of refraction as the cotton fibers. (The index of refraction is an optical constant that specifies how light is refracted upon entering the material. I(t also tells you the speed of light in that material). Even if the liquid doesn’t EXACTLY match the index of the cotton, it can still make the reflections smaller, rendering the shirt, if not completely transparent, at least translucent and (if in contact with what’s underneath) see-through.

That’s what happens with a wet T-shirt. The water, having an index of refraction of 1.333, is still somewhat lower than that of cotton (which is somewhere in the 1.4s, I think), but it’s enough to make the shirt see-through. But you don’t see perfectly – only the things that are in contact. Of course, because the shirt is wet, more is in contact. That’s the appeal of a wet T-shirt contest.

If you use oil on paper, the match is even better, but it can’t be perfect – in the first place, cotton fibers are birefringent, having different indices of refraction along different directions. In the second place, they put sizing in the paper to control the absorption of ink. They might have printing in either paper or T-shirts, and both may have fluorescent dyes added to make it appear “whiter”. All of this keeps either paper or a T-shirt from becoming completely transparent. Actually, even if these problems weren’t there, the paper or T-shirt wouldn’t become completely transparent, because it’s extremely hard to match refractive indices of liquids and solids over the entire visible spectrum. This leads to something called the Christianson effect, but I’m not going to get into that now.

[naita]

I’d also guess that the fibers in the wet shirt are less ‘fluffy’, hence more space inbetween them.

[Duke_of_Rat]

Sorry, Popup. I see the error of my ways now. I was transfixed by the wonderment of the wet tee shirt, much like the twinkling of the stars or the smell of the sea breeze, preferring to marvel in the beauty it held rather than to dissect the glory of it all into harsh, glaring, clinical terms.

I promise to do better next time.

[3.885AM]

White silk works best, but only for a short while. the underlying colors and textures come through more clearly, but it dries far to quickly.

[mangeorge]

What? No links? Examples of what you’re talking about would be helpful.
Peace,
mangeorge

[Spiff]

Anyone else here hoping that Cecil will answer this one in print?

The potential for Cecil’s trademark double ententres, bad puns, and wry writing style are astronomical.

I don’t see how he could not take this bait …