Why did the hot tub turn my white t-shirt blue?

May 21, 2007 6:45 PM

Why did the hot tub turn my white t-shirt blue?

A few weeks ago I visited a friend who has a hot tub and I forgot to pack my swimsuit. So I wore a white t-shirt and a pair of boxer shorts and a good hot tubbin' time was had.

When we got back inside and I changed clothes, I noticed that my white t-shirt was now blue. I rinsed it and rinsed it, and eventually ran it through the washing machine a couple times, but it still has a blue hue. Will this ever go away?

I recall during my growing years pouring bleach directly onto white fabrics that seemed to initally turn purple. I don't recall if I rinsed them right away to return them to their white state, or if they whitened up on their own. Same effect as the chlorinated hot tub + white t-shirt?

I'm not desperate to get this t-shirt white again, but am surprised that googling didn't reveal the answer right away. So I'm just damn curious. (And I'm filing the question under "science & nature" because I'm interested in the chemistry involved, not fashion.)

posted by iguanapolitico to science & nature (14 comments total)

Some people add blueing to pool water and hot tubs because the local water is naturally yellowish and looks ugly.
posted by Steven C. Den Beste at 6:57 PM on May 21, 2007

More on that.
posted by Steven C. Den Beste at 6:58 PM on May 21, 2007

How do you normally wash your t-shirts? Do you just use bleach or do you use some high tech detergent?
posted by JJ86 at 7:31 PM on May 21, 2007

Blue boxer shorts maybe? The dye could have bled and stained your shirt.
posted by maniactown at 7:38 PM on May 21, 2007

As a kid, swimming pool chlorine would turn my blonde hair green-ish in the summer. Here's why. Maybe what happened to your t-shirt is related?
posted by Brittanie at 7:46 PM on May 21, 2007

The shorts were indeed blue, but this was a very large hot tub. The t-shirt is blue all over, not just near the bottom where you'd expect to see dye running.

As for my detergent, I use bleach every few loads, but otherwise I basically use whatever detergent's on sale. Where are you going with that, jj? :)

At this point I want to blame bluing. Though, from that wikipedia entry I linked to Optical Brighteners, which are used in detergents to make dingy whites look whiter by absorbing uv and emitting visible blue ... but if the t-shirt was already bright white, would the blue look ... blue? :) And, of course, would an optical brightener be used in a hot tub? Or ... did all that chlorine in the hot tub make my shirt bright white, and the optical brightener was left over, in the shirt, from previous washings with detergent?

After all the rinsing and a couple washings it's definitely less blue, but it's as if the shirt emits a blue glow. Kinda freaky.
posted by iguanapolitico at 8:38 PM on May 21, 2007

Bluing is genuine blue dye. Often they use "Prussian Blue", ferric ferrocyanide (which is not toxic). That's a very intense and deep blue if it's concentrated.

Detergents often do include things which absorb UV and emit blue, but that's not what bluing does. It's just blue dye, and a lot of people use it in situations where they're trying to make unpleasant yellows go away.
posted by Steven C. Den Beste at 8:42 PM on May 21, 2007

Is the t-shirt polyester? Some cheap polyester turns bluish-gray when it's washed in hot water.
posted by boots at 8:42 PM on May 21, 2007

If your shirt is cotton and there was bluing in the hot tub, there's nothing you can do. It's dyed; it's gonna stay dyed.
posted by Steven C. Den Beste at 8:44 PM on May 21, 2007

All together now: "It's dyed, Jim."
posted by Steven C. Den Beste at 12:39 AM on May 22, 2007 [1 favorite]

I've never heard of people adding blueing for aesthetic reasons, but there is an alternative sanitizer called Cleanwater Blue that contains copper sulfate.

Ask your friend what he/she puts in the tub. The most common are chlorine and bromine, but I use potassium peroxymonosulfate with ozone.

And the overall hottub experience is better without the boxers or suits usually. (Although circumstances may vary)
posted by MtDewd at 7:27 AM on May 22, 2007

The hot tub is actually owned and maintained by the apartment complex. Therefore it's very big (not just your backyard hot tub for a couple people) and probably very chemically treated. (I remember being hit by the smell of chlorine when we got there, which I love.)

StevenCDB: I didn't mean to imply that the blue dye and the optical brighteners are the same, if that's the way it came across. I was just entertaining the possibilities of each.

Anyway, it was a nice, white cotton shirt, quite thin and it was always slightly sheer. It's barely blue now. When you turn it sideways you can see a lot of blue, but if you look at it straight on it basically looks white. At the beginning of this drama it was very blue. So if it's dye, it's not very good dye. :)
posted by iguanapolitico at 9:26 AM on May 22, 2007

First thing that occurred to me was memories of eating blue ramen while backpacking, as the water was treated with iodine and iodine is supposedly an indicator for starch. I know there are other pool/spa treatments than chlorine, perhaps one of the others has a similar effect? Although this is perhaps unlikely if you were assaulted by a chlorine smell.
posted by RikiTikiTavi at 11:31 AM on May 22, 2007

It's true that iodine and starch mixed together turns blue. But that would wash out.
posted by Steven C. Den Beste at 4:53 PM on May 22, 2007