You know the feeling. You’re doing the laundry, maybe you’re feeling a little tired or lazy–so you just kind of throw everything in. Now you’re folding everything and all the stuff that was white is now like… pink or blue or something. Probably a lesson everyone learns the hard way, and only has to learn once. Unless you don’t really care or exclusively wear dark clothes we guess. What makes this happen, though? Why do colors bleed in the wash?
Things lose their dye
Well, duh. Over time fabrics can lose the dye that colored them, which is why your clothes fade over time. Depending on the kind of fabric, your clothes may be more or less prone to bleeding. Generally speaking, synthetic fabrics tend to do better when it comes to holding dye. These fabrics include polyester, rayon, modal, and spandex. Their natural siblings are things like wool or silk. On the flipside, natural dyes tend to stave off both bleeding and fading better than their synthetic counterparts.
If clothes don’t have their dye adhere properly to the fabric for whatever reason, you get crocking. It can happen even without the wash, since crocking is just when dye is literally rubbed off something–and normally it gets rubbed onto something else. Normally this is only a problem if the dye hasn’t stuck itself to the fabric properly (something you get with really dark colors on raw denim more frequently than other combinations).
Bleeding is what happens with water. The water dissolves some of the dye and it can end up on something else. When it’s a problem, it’s because the “something else” was a white sock or something.
To mitigate bleeding, clothing manufacturers typically use dye fixatives or mordants. A mordant binds dyes to fabrics with a coordination complex. Coordination complexes are made of a central atom or ion and the ligands that bond to it. Atoms within the ligands are called donor atoms. This makes a coordination sphere, and normally the central atom in the sphere is some kind of metal. Mordants frequently use chromium(III).
Mordants are applied in pre, meta, and post ways. Pre-mordanting has your fabric treated with the mordant and then the dye. This forms the coordination complex on the fabric. Meta-mordanting just has the mordant with the dye bath and you do it all at once, where post-mordanting is just the opposite of pre-mordanting. The mordant is applied after the fabric is dyed.
What about red?
You might feel that red clothes tend to bleed more. This is because of the red dye that manufacturers commonly use. Red clothes are often dyed using a direct dye, and direct dyes are more susceptible to bleeding. Direct dyes are also more susceptible to reacting with ozone in the air and fading that way. It doesn’t have that much to do with the red pigment itself. Reactive dyes generally bleed less, since they form covalent bonds with the fabric they color.
Anyway, if you’re wondering how to prevent bleeding, using a cold wash will do you more favors in that department. This is because the hot water is more likely to wash the mordant out.
Here’s a laundry-themed word ladder if you finished folding everything and somehow aren’t fed up with all the clothes.