Science of Craft: 002 We're Dyeing (Cotton) All the Time

So I was on Pinterest the other day and ran into the same old shortcuts that I've seen since the beginning of Pinterest. I don't know what is so damn intimidating about dyeing that people are always looking for ways to customize clothing and fabric with anything but the very thing that will give you quality, permanent, and predictable results. I know "the establishment" isn't really popular right now, but dyeing the tried-and-true established way is actually pretty easy. Just go to Dharma Trading. Their instructions are easy, and every time I've had a question, they've been happy, like, really happy to help.

Now if you are interested in the seemingly not-easy part of dyeing, read on. I'll be discussing why all fabric coloring techniques are not alike, and why using Procion MX dyes are a superior choice for cotton, using what little I know about chemistry.

Dyeing Cotton

Remember my post on the chemical structure of cotton? You should take a look at it before proceeding. Anyhow, behold the star of the show below. This is cellulose, which is a popular fiber used in clothing.

A cellulose unit

The Hydroxyl Group

Try to find all six OH groups on the cellulose diagram above. These are called the hydroxyl groups and they are where the awesome stuff happens.

A generic hydroxyl group where the green thing could represent just about anything, even the rest of a cellulose molecule.

The hydroxyl group is where the dye molecule is going to attach. As you can see in the cellulose structure, there are a lot of places where this can happen. Six places in just one unit in fact. That's why cotton dyes so well, provided you use the right kind of dye and follow the instructions.

When I say, "the right kind of dye" what I'm talking about is fiber reactive dye. Not food coloring, not Kool-aid, not permanent markers, not paint, and for the love of all that is good in the world, not Rit-freakin' dye. Below is one example of the right kind of dye:

Orange 4

       
This is Orange 4, known as Procion MX 6 Deep Orange over at Dharma's. This is one of the colors I'm going to be using soon, and has one of the more constant structures, so that makes it a nice example.

Let's take a tour of this molecule. The complex part that I drew in orange is the chromophore. This is the actual color part. It absorbs and reflects certain wavelengths of light such that you see it as orange... Deep Orange. The part I drew in pink is the reactive group which will be binding strongly to the cellulose molecule. The grey part is the bridging group and it connects the chromophore to the reactive group. So there's three parts; the chromophore, the reactive group, and the bridge that connects them.

Now we just need to bind that reactive group of the dye to the hydroxyl group of the cotton. As-is, the hydroxyl group isn't really ready for a relationship. It needs to ditch the hydrogen before it can bond to the chlorine from the reactive group. The cellulose isn't into doing that at regular temperatures so you need an aqueous, basic environment to give it a little encouragement. What is commonly used is soda ash, which is often referred to as a dye "fixer." No, you can't just substitute the old box of baking soda that's freshening up your stinky fridge. Baking soda has the same structure as soda ash, less one sodium ion. That tiny detail makes all the difference in providing an effective solution for dyeing, so don't half-ass it. Get the right stuff. Anyway, once you place the cotton in a solution with soda ash, those hydrogens should pop off the oxygens, and be replaced with the chlorine from the reactive group. Like so:

One molecule of Orange 4 bonded to cellulose

That's a nice covalent bond right there folks. Just look at it. Covalent bonds are very strong bonds, making the dye a permanent part of the item you are dyeing. It won't fade, wear out, rub off on other items, bleed in the laundry or any of that. This is why fiber reactive dyes are so superior.

Plus, if you ask me, the whole thing was pretty damn simple. You have your cotton, your dye, and a chemical that helps the dye bind to the cotton. You don't have to iron it, steam it, or add vinegar to make it stick. In all my years in the craft industry, I have heard every weird "trick" for adding color to fabric and I seriously don't know what compels people to try these things other than that Rit, food coloring, vinegar, and irons are things that can either be easily acquired at the grocery store or are already available in the home, and that somehow creates the illusion of cost-effectiveness. Or maybe it's just cute to say you colored your shirt using Kool-aid and a microwave. Anyway, these things just do not bind to your fabric in the same way that fiber reactive dyes do, that is, if they bind at all.

Now, what about paint? It's a legit practice. Screen printers usually use paint to make your graphic T-shirts after all, plus, there are plenty of paints made specifically for fabric. As an 80s baby, I have a special love for puffy paint. However, there are huge differences between dyes and paints. Paint, whether it's for fabrics or some other application, is made of a pigment or colorant that is unable to bond with the fabric fiber the way dyes do. So, the pigment has to be mixed with a glue that will bond the color permanently to the fabric.

The thing I don't like about fabric paint is that it alters the hand or feeling of your fabric, often making it stiff or rough. Fabric paints, especially ones with a lot of white in it, don't wear incredibly well either, often cracking or flaking off. Dye-na-flow paints don't have this problem, and I used them a lot during my silk scarf period, but I wonder why the hell I didn't just use dye then.

Anyhow, if you're ready to dye, I'd steer you towards Dharma Trading's Tub Dyeing Instructions, as these are more or less the instructions I'll be following. I documented my process here.

If you're interested in learning more about the chemistry of dyeing, I'd suggest Paula Burch's site. I have learned a lot from her writing which has improved my results.