General Question

robmandu's avatar

Why do black things, when bleached, turn orange?

Asked by robmandu (21280points) August 25th, 2008

Dyes, chemical reactions, etc… just curious. You’d think (hope) it’d go to gray. Actually… how would one attempt to guarantee that bleaching a black garment would yield gray, not orange?

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11 Answers

wildflower's avatar

This is a guess based on my very limited knowledge of colour theory….

It may have something to do with getting better results with dark colours if there is a strong presence of red. I know this is the case with hair (yes I learned the hard way), you shouldn’t attempt to add a dark colour on top of very light/bleached hair without giving it a red base first (results may be green-ish or blue-ish, depending on the composition of the black you’re using).
Same thing with textile dyes – I guess. For best results, pre-treat with red so as to deepen the dark/black “colour” (black technically isn’t a colour in itself, but that’s another discussion)

Even without pre-treating, it may be that the predominant colour in the black composition is red/orange and those are therefore the most stubborn when removing the colour.

Sueanne_Tremendous's avatar

First off, you say “when bleached”. I assume you mean chlorine bleach. There are other bleaches (oxygen, for one) that are color safe. If you used chlorine the answer is simply that you didn’t use enough chlorine, or you didn’t use a strong enough concentration to remove the black color completely. Most household chlorine has a concentration level of around 5%. You want to use something around 10–12% to get good bleaching. Even with strong bleach you will need multiple times doing it to get to the color level you expect—and then, it probably won’t be uniform. Good luck.

A couple of other things. Chlorine works best at 150F or higher and likes a pH range above 10 but less than 12. In this range you can get color removal with minimum fabric damage. Also, make sure you rinse the fabric well be fore drying. if chlorine is not exhausted in the wash it will become active from the heat in the dryer and can rapidly degrade the fabric.

AstroChuck's avatar

Because there is no such thing as black dye. It’s just very dark shades of colors, whether it be green or brown or red. I would guess the orange would come from a very dark red dye.

robmandu's avatar

huh… according to Wikipedia, Sulfur Black 1 is the largest selling dye by volume.

AstroChuck's avatar

rob- Black can only be obtained with the absence of light. There can be no reflection. They call it black dye because that’s how it appears to our imperfect human eyes. That is why bleaching “black” fabric brings out color.

robmandu's avatar

Yah, I get that. Your point is that it appears black because it’s just a really, really dark shade of some color.

However, when I read something like “there is no such thing as black dye,” I tend to want to find out more for myself. So far, I keep coming across info related to dyes that are indeed called black.

So, how ‘bout helpin’ a brutha out? Got a link or other reference? I’m actually interested in large part because you said it. ;-)

wildflower's avatar

This would be a decent starting point

gailcalled's avatar

I made a quilt using some black cotton fabric. Then closed up the summer home where it was resting on a bed. 9 months later, when we reopened the house, the black areas exposed to sunlight had faded to a drab light brown..

gailcalled's avatar

edit: Quilt and not summer home was resting on bed.”

susanc's avatar

Because bleaching can be very destructive to fabric, how about redyeing the now-orange
garment with the color-wheel-opposite color, which would be a lightish blue?
Getting more and more orange out will not give you grey, just shrimp followed by pale-peach followed, ultimately, if the garment isn’t in shreds, white..

robmandu's avatar

Well, you see, I didn’t bleach a black thing accidentally. That was someone else. I’m just curious is all, having seen it before.

Thanks just the same.

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