Why does salt need to be added to clothes dye?

I recently bought some dye to recolour some old clothing (more specifically a pair of handwraps and some hankies which have been stained by excessive use and being exposed to a leaky pen respectivly). The instructions state that I need to also add 500g of salt, regardless of how many packs of dye I use.

What is the purpose of the salt? While I’m asking, is there a way I can forgo it, since it would mean going out of my way to buy some?

It helps the material absorb or attract the dye.

By creating an ionic solution, salt will help the chemical reactions that bond the dye to the fabric work more efficiently.

It is the same reason that adding a little salt to food makes it taste more intensely like itself, while adding too much salt just makes it taste salty.

I came back to add it’s a ionic attraction which I skipped the first time. It’s already mentioned so carry on.

Stand back everyone. We’re using SCIENCE!

You want your clothes to taste good, don’t you?

So I’m still going to have to go out and get myself 500g of salt? grumble

Come to think of it, why doesn’t clothes dye come with the salt as part of its composition?

Well, the instructions say to add 500g no matter how much dye you’re preparing, which means that the 500g is the standard amount. If they put salt in every dye packet, what happens if you’re preparing a big vat of the stuff to dye 15 pairs of jeans or something? You’ve easily got 2 or 3 times the salt you need, and it goes from being an ionic helper to being a crusty mess. Better to have the dyer add just 500g and avoid that possibility.

Because each packet would be bigger and weigh more than a pound, and the manufacturere would have to pay for warehousing and shipping that much more stuff. To say nothing of being ready prey to the whims of the international salt cartel.

Oh, yes, and the grocery stores where dyes are sold might not take kindly to the vastly increased shelf space needed to stock such bulky dye packets.

Do you know the mechanism on how an ionic soltution helps the dye bond to the fabric better? Right now it isn’t making much sense to me…its a bit nebulus

It doesn’t bond better. Direct dyes, like the salt-moderated component of Rit, aren’t colorfast with or without salt. What the salt does is to get more of the dye molecules onto cellulose fibers, which is why Rit says, “For best color results when dyeing fabrics containing cotton, rayon, ramie, or linen, add 1 cup salt…” (Rayon, though “synthetic,” is actually cellulose). Salt is not necessary in a small container of concentrated dye, only when the dye is dilute, as in a washing machine. Dye molecules are constantly jumping on and off the fibers and associating and disassociating with water molecules. Salt ties up the water molecules so that the dye spends more time with the fibers, and ultimately more dye ends up in the fabric. This is, by the way, the same mechanism that allows salt to thicken shampoos, which is why some manufacturers make a big deal about their “salt-free” formulas.

this guy postulates it helps to overcome ionic repulsion between the fabric and dye which could well be right

Sorry Charlie.

Anyway, why don’t you need more salt with a bigger pot (and more dye)?

Quite simple, actually. It just … LOOK! A Monkey!!!