Bleach doesn't always work?!

July 12, 2007 6:49 PM

I sat in bleach. Why didn't it turn my chair white?

It turned my jeans white with no problem. It dampened the seat in my wife's truck but didn't change the color. Why not?

The bleach: regular sodium hypochlorite laundry bleach
The jeans: blue cotton denim
The upholstery: course weave, blue and grey, something like polyester.

Guess 1: The dyes or pigments in the truck could be inorganic chemicals that aren't affected by bleach (like cobalt blue instead of indigo).

Guess 2: When you dye cotton, it sticks to dye sites on the outside of the fiber, but when you make polyester you can mix the dye in, all the way through the fiber, where bleach can't get to it.

Guess 3: I know nothing about dying or bleaching fabrics, so it could be something else entirely, and the hivemind here could have a completely brilliant alternative explanation.

I don't know how many dye chemists we have here, but thanks in advance for your answers!

posted by rossmik to science & nature (4 comments total)

Guess 2 is right, more or less. Polyester and other synthetic fibers have their color added at the solution stage, before the liquid is spun into fibers. So the color is pretty much inherent at the molecular level. I believe bleach can affect some synthetics, but apparently not this one.
posted by doift at 6:55 PM on July 12, 2007

By the same token, it's very hard to dye synthetics. If you've got something made of cotton sewing with polyester thread, the cotton will take dye but the thread will stay white. It makes for some unpleasant surprises when people try to dye a piece of clothing and end up with white stitching where they didn't expect it to show.
posted by katemonster at 7:24 PM on July 12, 2007

Sewn with. Not sewing. Sewn.
posted by katemonster at 7:48 PM on July 12, 2007

Thanks doift, I didn't know if that was actually possible, or if the dyes would interfere with the polymerization process somehow. And katemonster, that's a fascinating additional detail. Thanks!
posted by rossmik at 4:06 PM on July 13, 2007