The science of how to dye yarn
Have you ever looked at a plain, undyed hank of yarn and seen the possibilities? Take a journey with Angie and discover the science of how to dye yarn in this 4 part series.
I’ve always wanted to learn how to dye yarn. I’m an unrepentant lover of tonal shades inspired by landscapes and cityscapes alike. I wanted to learn how to create the gorgeous greens and brilliant blues that inspired me in my day-to-day life, but I knew I had to start with the science before I could be successful in my venture. Join me on my quest to learn everything there is to know about home-dyeing yarn – and let’s start with science.
First off, let’s talk about different yarn fibers. As many will already know, it’s relatively easy to dye animal fibers at home, but significantly more difficult to dye plant fibers. This has to do with the cellular structure of these fibers, and how they chemically bond with different types of dye.
As you can see, the structure of wool and other animal fibers is very different than a plant fiber. The same scales that cause animal fibers to felt can aid the dyeing process.
There are a few different kind of at-home dyes that can be used on yarns. Acid dyes, like food coloring and Kool-Aid, natural dyes like beetroot and tumeric, and all-purpose dyes, like Rit and tie-dye kits. The yarn takes color differently based on the kind of chemical bond that forms between the fiber and the pigment.
Acid and natural dyes
Natural dyes are in effect the same chemical reaction as an acid dye. An acid dye reacts in an acidic environment to form strong hydrogen bonds with the proteins in the animal fibers. This is the easiest kind of dye to achieve at home for a beginner, with little to no prior knowledge of yarn dyeing.
Different pigments bond differently in different acidic environments. When using Kool-Aid to dye, no additional materials are necessary due to the naturally occurring citric acid in the flavored powder. When using food dye, however, the addition of vinegar is necessary. Because water has a neutral pH, acid dyes will not work without a little bit of chemical help. Vinegar is 3% acetic acid, and assists the hydrogen in bonding to the protein fibers.
When using natural dyes, sometimes a mordant is needed to strengthen the Hydrogen bonds. This can be alum or even Cream of Tartar – the latter of which can be found in most baking aisles.
In addition to Hydrogen bonding, acid dyes also typically contain extra molecules that form a “salt linkage” with the proteins and molecules in the animal fibers. These “salt linkages” are ionic bonds.
The above example demonstrates the chemical bond between Sodium and Chlorine, which makes everyday, run of the mill table salt. Molecules want to have a stable set of electrons, which means eight electrons in the outer shell. As you can see, Sodium has an extra electron floating around. When it meets Chlorine, which only has seven electrons in its outer shell, they bond together and the Chlorine “borrows” the extra electron. Ionic bonds are fairly strong and are responsible for the reliable washfast properties of an acid dye.
These dyes, like Rit and others, are most useful when dyeing fiber blends. All purpose dyes contain both an acid dye, which works on animal fibers, and a direct dye, which works on plant fibers. It is not effective on acrylics. Because it contains two forms of dye, there are two different chemical reactions that take place when it meets a fiber blend. If only one fiber is present, the other chemical reaction is wasted and remains unused. For this reason, it’s not generally recommended to dye plant fibers with all-purpose dyes, because it becomes difficult to tell when all the dye is taken up. (Don’t worry, we’ll chat more about that later.) In addition to that, direct dyes can only form weak hydrogen bonds, and have trouble retaining pigment when washed.
Fiber reactive dye
In order to create reliable, washfast dyes for plant fibers, textile manufacturers had to come up with a different solution to acid dyes and all-purpose dyes. The result was fiber reactive dye – it’s most effective on cellulose fibers like cotton, linen, and bamboo, but also works on protein fibers.
Fiber reactive dyes incorporate more chemistry than most knitters are comfortable with (myself included), but the most important result is that it creates a covalent bond.
The above example is a CO2 molecule, also known as carbon dioxide, which we breathe out. Each Oxygen molecule “shares” an electron pair with the central Carbon molecule. Covalent bonds are very strong and resistant to breaking – that’s why you can wash a cotton t-shirt dozens of times before you see any fading.
If you want to find yourself a fiber reactive dye, your best bet will be a tie-dye kit, which already has the soda ash additive mixed into the powder. This is the best option for dyeing plant based yarns.
Stay tuned for the next 4 installments of how to dye yarn – starting with Kool-Aid next week! Follow us on Bloglovin’ so you don’t miss any of the how to dye yarn tutorials.
Last updated: August 1st, 2017.