So, there are a lot of dyes out there in the world, made by a lot of different companies.

The most common kinds you will run into are as follows:

Acid Dyes

Direct Dyes

There are subclasses of most of these, and some crossovers. I’ll also briefly touch on a group called “Disperse Dyes.”

Ok. So, the difference between each of these classes of dye is in the way they interact with the fiber you’re dyeing. That is, they have a different chemistry. No, not scary! Get back here! I’m going to explain things logically and slowly, and if you have questions, feel free to ask them. I’ll try not to overwhelm you with jargon without explanation.

I’m going to go through them from one end of the chemical spectrum to the other, starting with my favorites, acid dyes.

Acid Dyes:

First, what does this group include? Some of the things you’re probably familiar with…

Kool Aid
Most food dyes, especially reds

and some you’re likely less familiar with…

Jacquard Acid Dyes
Prochem Washfast Dyes
Greener Shades Dyes

And more! But they all work via a similar chemical mechanism.

I’ve posted about acid dyes before, but I’ll duplicate some of it here.

First, the “acid” in “acid dyes” refers not to the dyes themselves, but to the environment they bind in. For kool aid, the acid is already present in the mix (in the form of citric acid crystals), for other dyes, it’s added as vinegar (which is acetic acid) or sometimes citric acid.

Safety Sidenote: Both acetic and citric acid are food acids, that is, they’re not terribly toxic and won’t kill you. However, when dealing with concentrated citric acid, or any hot bath with acid in it, be careful. Inhaling large amounts of vinegar steam can irritate your throat and lungs and eyes. Submerging your hands in these acids for any length of time can cause irritation and some skin peeling. Better safe than sorry.

Now, some acid dye chemistry!

Acid dyes work via a combination of interactions with the fiber. I’ll explain each one.

Primary: Ionic bonding
Secondary: van der Waals, Hydrogen bonding

Ionic bonding is a bonding between different charges on two molecules. Imagine acid dyes like little magnets. Remember how if you put two magnets together, you have to put the S and N ends together, or they’re push instead of pull together? Some molecules work the same way.

van der Waals interactions are like mini ionic interactions. Instead of a whole magnetic pole interaction, it’s a tiny fraction of one. But they add up.

Hydrogen bond interactions are weaker than ionic and stronger than van der Waals interactions, but use the same idea but specifically involving hydrogen.

Acid dyes are “anionic” meaning they have one full negative charge, think of it as one “south” magnet end.

Acid dyes can therefor bind to fibers which are “cationic” meaning they have one full positive charge, or one “north” magnet end.

An acid dye binds, like a magnet, when its “south” end binds to a fiber’s “north.”

There are many different ways to build an acid dye to get this “south” magnet effect. Some are strong, and some are weak. Here are a few examples.

You’ll notice that in all of these examples, an SO3 group (or two) is present. This is the “south pole” for these dyes. The rings are what gives it color.

Acid Orange, many reds and oranges are shaped like this.

Acid Green, many if not most greens are shaped like this. Some purples and blues as well.

Acid Blue, this overall elongated structure is what a lot of the “leveling” dyes use.

A “leveling” dye, is a dye which naturally makes for a more even color coating. The way this is done is by making a dye molecule with weaker binding potential (a weaker south pole) so that molecules can bind and unbind to move about the fiber evenly. This is convenient, but the trade-off is that the dyes can come off the fiber even when you don’t want them to. This is annoying if you want to wash your fiber in warm or hot water.

Another concern that many have with acid dyes is that to get the deeper and intense colors, especially blues, many of them are made with metal ions…

For example, here’s ProChem’s black dye, acid black. It’s a “true black” or “primary black” meaning that it’s not blended. But the intensity of color comes from that “Cr” in the middle of the molecule, which is a Chromium atom. Chromium is a heavy metal, which makes this a dye you don’t want to pour into your groundwater.

(You’ll notice this dye, as well, uses the “sulfonate” SO3 group as its ion, but also has a “nitro” NO2 group as well)

As a rule, companies try to limit the amounts of these heavy metals they need to use, and some companies like Greener Shades try to eliminate them altogether. However, some colors are hard to get without the use of metals.

So, in short…

Acid dyes are anionic (south pole) dyes, which use heat and an acidic environment to form ionic bonds with fiber.

Direct Dyes:

Dyes in this category are…

Cushings Direct Dyes
Jacquard iDye Direct Dyes
ProChem’s Diazol Direct Dyes, now sold by Aljo Mfg.
Any “universal” dye like RIT will have a Direct Dye as one of the two components

Direct dyes also use a combination of forces to bind to fiber…

Primary: van der Waals
Secondary: Hydrogen bonding

You can see already, that in some ways they’re similar to acid dyes, but their primary binding mode utilizes a much weaker interaction. Still, they bind similarly to similar fibers.

Direct dyes tend to be very large in order to have more “subtantivity.” This means having more surface area to contact the fiber and engage in more of these small van der Waals interactions.

Many if not most of the direct dyes will function as acid dyes as well. Look at this Direct Red dye and you’ll see why…

See that SO3 group? Yep, acid dyeing group. The problem with these dyes is that being as long as they are, and generally more balanced along their length, they again are easier to dislodge. You’ll notice it looks almost identical to the “leveling” category of dyes, that’s because… the classes overlap! More on what this means when I get to fiber chemistry in the next Dyeing 101 post.

You’ll also notice there’s more H’s hanging off, hydrogens that can be used in hydrogen bonds to stick this dye to fiber that doesn’t have that “north pole” that the acid binding group (the SO3) needs.

Since these dyes rely generally on weaker interactions, they are less washfast and lightfast than most acid and reactive dyes. Being big and floppy, they also tend to be duller in color (though this trait is not uniform). The advantage of them is that they don’t require fiber with positive “north pole” groups.

So, direct dyes in brief…

Use some ionic, but mostly hydrogen bonding and van der Waals forces to bind to fiber. Less wash and lightfast than reactive or acid dyes, but better leveling and don’t require cationic “north pole” groups to bind.

Reactive dyes:

Dyes in this category…

Procion MX
Dylon Cold
Lanaset/Sabraset
Cibacron F
Prochem Sabracron F
Remazol
Vinyl Sulfone

Reactive dyes us primarily a singular mode of binding, though most can use another as well.

Primary: Covalent bonds
Secondary: As acid dyes

Covalent bonds are what you think of when you think of molecules. “Actual” bonds. The kind that hold the H-O-H of water together. Those little lines in all these diagrams are covalent bonds.

Covalent bonds are the strongest bonds, as such reactive dyes are the toughest when it comes to being washfast.

I wish there was a better picture of this, but here’s a common reactive dye molecule…

The first thing you might notice is those SO3 groups. That’s what makes this able to function as an acid dye if you add vinegar.

But here’s the important part of the molecule, over there on the left…

Funny looking bit, isn’t it? Chlorines (note that when on the dye, one chlorine is replaces with the dye)? Negative charges? Those chlorines would really like to rip a hydrogen off of your fiber and float off happily as HCl (Hydrochloric acid), but that would leave that ring behind it bare! But wait, whatever is behind the H the Cl ripped off is ALSO bare, usually an O or an N (Oxygen or Nitrogen) so the two bare things can interact and form a new covalent bond, yay!

That means when the process is done, you have a dye molecule that is actually PART of your fiber molecule, pretty cool? And depending how those interaction groups are designed, they can react with all SORTS of things. Neat. The highly basic environment most reactive dyeing is performed in is to make this process easier, similar in reverse to why acid dyes are done in an acidic environment.

So, an overview of reactive dyes…

Covalently bonded to oxygens and nitrogens on the fiber, making them ultimately washfast. Lightfasteness varies with the structure of the dye molecule.

Disperse Dyes:

Disperse dyes are horrible and gross. They’re what you have to use to dye polyester and acrylic and similar plastics. Ok, that’s not all true. There are ways to dye polyester without having to use the noxious chemicals and super heat, Jacquard has dyes for it. But they’re still not pleasant dyes. I’m not going to talk about the chemistry of these.

Brief overview for those who want the differences quick:

Acid Dyes: Anionic (negative), bind to cationic (positive) fibers. Can’t bind nonionic fibers. Fairly washfast, pretty lightfast.

Direct Dyes: Often anionic (negative) binds to nonionic fibers, and if anionic then it can bind cationic fibers as an acid dye. Not very washfast or lightfast. Many can be used as weak acid dyes. A component in “universal” dyes like RIT

Reactive Dyes: Covalent interactors, often with anionic (negative) bits as well. Given the right environment can bind covalently to nonionic fiber, and possibly to cationic fiber. Many can also function as acid dyes on cationic fiber.

Now, I’m sure by now you’re waiting for me to tell you WHAT fibers are cationic, and what fibers are nonionic. You might be wondering if there’s anionic fibers too. We’ll get to that, but not in this post. That’s in the next post. Cellulose, protein, animal, plant, extruded?

::waves:: As I said above, feel free to ask questions, clarify, or even argue with my chemistry.

Answers to Questions:

To Velma: By wandering around the web a lot. Here’s what I can tell you about ProChem’s stuff…

Sun Yellow, Basic Red, Bright Blue Red, Turqoise, Bright Blue, and National Blue are all non-metallic. Carbon Black (Acid Black 52) is the chromium containing one. Here’s a link which has some minimal information. As a rule, if you Google either the systematic name or the Color Index name, you can find the structures of things. So for example… Acid Yellow 17 Sigma can be a good place to find these.

To Krissy: Usually, that’s how those fibers are dyed, from what I understand. They’re colored in the vat, before extrusion.

Kellie: Feel free to link away. And anyone who comes here from there can also feel free to ask questions or make comments.

Diane: An ionic bond is like a magnet. It can only occur between two things which are magnetizable (or in the case of ionic bonds, things which have charge). So, like you can’t stick a magnet to plastic, you can’t stick an ionic compound to a non-ionic one.

David: The next big post in this series will cover the basic difference between fibers, animal, plant, and others.

~The Gnome

Well here it is, finally. I was dyeing again (also fnally) last night, and was thinking about this again. This post is a little more chemistry heavy than the last one. Feel free to ask questions if things are unclear.

So, fiber reactive dyes are slightly different than acid dyes. Acid dyes work by loose associations with fiber. So while they are “fast” (don’t tend to wash out) they’re not actually “bound” in the chemical sense. That is, if you drew a picture, there are no hard dark lines between the chemical structure of the dye and that of the fiber, just dotted ones.

Fiber reactive dyes take those loose associations one step further to make actual chemical (covalent) bonds with the fiber. One reason for this is that plant fibers are slightly basic, while animal fibers are slightly acidic. That means that an acid dye (which requires an acidic environment to stick) will never stick to the basic plant fibers.

Here’s an example of a reactive dye. As usual, you can ignore most of it because the really big parts are just to make it have color. The important part is that SO3 part in the top right. That’s our “reactive” group.

This particular dye has a masking group on the reactive part (The Na – sodium – to the right, plus one of the O’s) which prevents the dye from reacting with water (that SO2 sulfur dioxide group LOVES to react with things) until you either boil it or add a very basic compound like soda ash to knock the sodium off. Then the C-SO2 can bond with an C-O-H on the fiber and make C-S-O-C which is muuuuch more stable.

I suppose I should note here that this is not a typical reactive dye, structurally. Most reactive dyes are unmasked and use a slightly different reactive group.

This is a Procion Yellow dye. In this, the loops behind the chlorine (Cl) are the reactive groups. The chlorine comes off, and the ring reacts with the cellulose to make an “ether” bond, C-O-C (the corners of the rings are C, carbons). The chlorine (unlike the NaO above) is more than happy to fall off as soon as you add water, so it’s called a “leaving group” instead of being a masking group that has to be knocked off.

Dyes like Procion MX don’t have that masking group, so you can’t put water in them until you’re ready to use them, ’cause that reactive group will react with you water! Then it can’t react with your fiber anymore, and much sadness abounds. However, not having the group means that you don’t have to get the masking group off at all, which means almost all your dye will react with something, even if it’s the water. So, if you’re fast, the non-masked dyes are “more reactive” (more of it will react with your fiber) than the masked dyes.

If you actually want to do fiber reactive dyeing, Knitty has a good article.

~The Gnome

Which, of course, left you saying, “Well that’s great, but now what?”

Ah, now what? Now we discuss solutions.

The “easy” thing to do, would be to replace the water. Because water doesn’t get along with our yellow (and to a lesser extent, the red), because magnets like magnets, and our yellow… well it isn’t a magnet.

So, what would be easiest would be to make the solution the dye is dissolved in also be a not-magnet, balanced, hydrophobic (water hating) molecule. Unfortunately, hydrophobic solvents are generally highly caustic and thus not available. Things like… phenol and formaldehyde and benzene (Benzene is just those rings I showed you yesterday).

Ew. Even if your average dyer could get those chemicals, you wouldn’t really want your yarn/fiber soaked in gas, or flesh dissolving goop. Neither would these chemicals play nice with your green and blue dyes, which are hydrophillic magnet molecules.

So, we can’t replace the solvent (what the dye is dissolved in), and we can’t change the dye itself (since then it wouldn’t be yellow anymore). What can we change?

The answer is, anything that doesn’t affect the dyeing chemistry itself. Which means we can add quite a bit of stuff to our dyepot without screwing up the dye.

The most straightforward things to add are things which will interact with both hydrophillic magnet molecules and non-magnet hydrophobic molecules. So, molecules which have a balanced end and an unbalanced end.

These fall into two classes: Detergents and Humectants

Detergents. Detergents are molecules which have a hydrophillic “head” and a hydrophobic “tail.” Your laundry “detergent” is a detergent (in the chemical sense). And the way it works is by forming little groups around your hydrophobic dirt particles, tails (non-magnet ends) pointed in at the dirt, and heads (magnet ends) pointed out at the water. This lets you wash the dirt off with water.

“Soaps” are a specific kind of detergent scientifically called “surfactants” or “surface active detergents” because they have a higher than normal ability to wrap all the way around those little hydrophobic dirt particles, even if that means pulling them off a surface (you, your clothes, etc).

So, you might be able to add some detergent to your dye bath to help the yellow go into solution. The problem is that most commonly available detergents are soaps, which means they are really good at sequestering things (wrapping all around and not letting it touch anything) which can inhibit your dye’s ability to, well… dye. So, go ahead and add a little detergent (the naturally less foamy your detergent the more likely that it will help) but it may or may not solve the problem.

Humectants. These are similar in overall structure to your detergents. They have a hydrophillic and a hydrophobic end, just like detergents. The difference is that their hydrophillic end is REALLY hydrophillic. They don’t just get along with water, they actually hold onto it. The other difference is that your humectants are less able to gang up and “wrap around” hydrophobic molecules, so they won’t stop your dye from interacting with things. Basically, they can make believe that your hydrophobic molecule actually likes water. This is why they’re often called “wetting agents.” (Humectant, from the same root as “humid”)

These are overall a better choice than the detergents, and are fairly readily available. Glycerol and urea are the two most common ones. Urea is generally cheaper, but smells funny and in very large amounts can screw with things. Glycerol is a little gunkier to deal with but doesn’t interact with just about anything (beyond the aforementioned humectant property).

Salts. If you have especially soft water (lacking in calcium and magnesium) then a small addition of salt can help to increase the disorder in your solution, but it’s not likely to help a great deal unless your water is REALLY soft (if you scrub forever in the shower and that detergent never comes off you, same reason).

The short answer:
So, if you’re having trouble with crashing or goopification, try adding a little detergent. If that doesn’t work, try adding urea or glycerol.

Or, use the tried and true method of increasing your free energy and system entropy… put it back on the stove or in the microwave, and heat it up again!

And yes, for those of you wondering, I will post about non-science stuff. Maybe even tomorrow. I might even talk about… knitting! Or you know, that spinning stuff I do!

~The Gnome