In March 2024, I joined a natural yarn dyeing course. It was more chemistry class than craft session — and I loved every minute of it.
I have been a yarn connoisseur for some time. My stash would suggest I am physically incapable of passing a good skein without acquiring it. But until March 2024, all the yarn I owned had been dyed by someone else. I had admired hand-dyed skeins from afar, wondered about the processes behind the colours, and occasionally browsed natural dyeing books without quite committing to actually getting my hands (literally) into a dye pot.
Then I signed up for a natural yarn dyeing course. And I discovered that dyeing yarn is, at its core, a chemistry class. A deeply enjoyable, occasionally smelly, thoroughly absorbing chemistry class.
What We Dyed
The class centred on dyeing seven sets of 20g balls of superwash merino yarn, each with a different natural dye plant or extract. The roster included: madder, weld, logwood (extract), woad, onion skins, walnut husks, and Saxon Blue. We worked primarily with alum as the mordant, with iron and copper as modifiers where appropriate.
Seven dyes sounds like a lot to cover in one session, but natural dyeing has a wonderful rhythm to it — once the dye baths are prepared and the mordanted yarn is in the pot, there is a waiting time that lends itself to conversation, observation and note-taking. Each bath produces its colour slowly, and the transformation of the yarn from its creamy white to a range of earthy, botanical tones is genuinely satisfying to watch.
The Star: Madder
Madder (Rubia tinctorum) is one of the oldest dyes in the world, and it produces a warm, earthy red that immediately conjures autumn leaves and terracotta pots. With alum, our yarn came out a beautiful brick-red. The chemistry instructor explained that the same madder root can give orange, red, burgundy or even purple depending on the mordant used — a fact that I found extraordinary, and which I have since seen confirmed in my own experiments with iron-modified madder.
The Surprise: Weld
Weld (Reseda luteola) is the dye plant I knew least about going in, and it produced one of my favourite results: a bright, almost luminous golden yellow. Celtic and classical dyers used it frequently in combination with indigo to create green — and our instructor demonstrated this by overdyeing a weld-dyed sample in woad, producing a beautiful sage green that I am still thinking about.
The iron-modified weld, however, was the one that really caught my eye. By adding a small amount of iron mordant to the weld bath, the golden yellow shifts dramatically into a deep, saturated green. The chemistry is direct: iron “saddens” the yellow tone while shifting its hue, and the result is the deep weld green that I later used as the background for my weld embroidery sample.
The One I’m Most Careful With: Iron
Iron was the mordant I found most enjoyable to work with — but also the one that required the most discipline. Its transformative effect on colours is remarkable: it deepens and shifts virtually every dye it encounters. But it is also abrasive to fibres over time, and the run-off is harmful to waterways. Our instructor was clear: iron has a dedicated pot, separate from everything else, and the bath water is never poured straight down the sink.
I came home from the course with wet yarn that dried overnight into the colours you see in the photograph opposite. I still have all of it, wound into beautiful little skeins. I am almost too fond of them to actually use them — which is, I suspect, a hazard of making something by hand.
What the Skeins Look Like Now
From top left: Weld, Iron-modified Walnut, Logwood Extract, Saxon Blue. From bottom left: Iron-modified Weld, Onion Skins, Iron-modified Onion Skins. Each one represents a distinct combination of plant, mordant and process — and each is a colour that exists nowhere else in quite this combination.
The logwood extract gave a deep purple-grey that I find difficult to describe and have not yet used. The Saxon Blue (a historic blue dye made by dissolving indigo in sulphuric acid) produced a clear, cold blue quite different from the warmer woad blues. The walnut husks produced a deep, warm brown that is earthy and beautiful but requires careful handling, as walnut can also act as a mordant in its own right and can affect subsequent dye baths.
Would I Do It Again?
Without question. Natural dyeing is one of those crafts that sits at the intersection of science, history and creativity in a way that few others do. Understanding the chemistry of mordants deepened my appreciation of every hand-dyed skein in my stash, and gave me an entirely new way of thinking about colour — not as something applied to yarn, but as something that emerges from a conversation between plant, fibre and chemistry.
If you have not tried a natural dyeing workshop, I would thoroughly recommend it. Just wear clothes you don’t mind staining, own a set of dedicated pots, and resign yourself to the fact that you will come home with yarn you cannot bear to use.
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