Curly Dock Mordant

Dock or sorrel are useful plants for mordanting – this was a fact that I’d gotten from reading and made a mental note of. I couldn’t remember where I read it, so I decided to just go ahead and try it. I picked curly (or curled) dock (Rumex crispus) in the roadside around July-August. Curly dock is a tall plant with a reddish seedhead.

The seeds of curly dock.

Curly dock can be distinguished from other related species from the fact that its seeds are enclosed by three petals that have a growth on the outside that looks like a seed but is not.

Enclosed seeds of curly dock.

I used about 100 g of stalks with flowers for a test skein of about 12 g of wool. I boiled the curled dock the first day and let it cool off. The next day, I heated the yarn in the sorrel bath to just under boiling, then let the yarn cool off in the sorrel bath (for a couple of days in the end, because I had other fish to fry). After the sorrel mordanting in the dark red sorrel soup, the yarn was coral red.

The concoction of curly dock, and yarn treated with it.

Finally to the dyeing part of the experiment. I dyed my sorrel mordanted yarn plus two other 12-g test skeins (one unmordanted and one mordanted with 10% alum, my standard mordant) with madder. The dye bath was 40 g of madder root in rainwater, and you can see the result below. As expected, the alum mordanted wool is an intense madder red, but the unmordanted and sorrel mordanted wools are the exact same shade of orange (and a nice orange I think). But I’m going to call this a failure, since the sorrel mordant didn’t make a difference from no mordant.

Alum treatment gives the usual madder red – no mordant or treatment with curly dock both give orange.

So what went wrong? In the end, I realized that I read about sorrel mordant in India Flint’s “Eco Colour”, the exact information she gives is:

“Dry and grind the roots and mix with water to make a tannin-rich soaking solution. The leaves of this genus are also rich in oxalic acid. Even the dried seeds have mordant qualities.”

This doesn’t completely solve my mystery, though. The roots contain tannin, which only works as a mordant on plant fibers, not wool. But I used the flower stands with leaves, which (like rhubarb leaves) contain oxalic acid, which should work as a mordant on wool. Maybe the amount was just too low? I have to try tris again next year.

An Experiment in Cold Mordanting

Recently, I have wondered how much it is really necessary to heat wool when you mordant it. To the usual 80-90C? Or would 60C be enough? (Yes I wondered about that because I ruined some yarn, and I think I overheated it!)

So I turned to the knowledgeable people on Ravelry’s natural dyeing forum for help, and was told that you can cold mordant. No heating, just steep the wool in the usual alun solution without heating it. And for how long? Sea green and sapphire writes that it is enough to leave it overnight in a cold solution, and that “dyeing results are not compromised in any way by leaving out the heat”.

So it had to be tried! I took:

  • One 10 g test skein of wool, mordanted in my usual way: prepare a solution containing 10% alun. That means if you have 100 g of wool, put 10 g of alun in the pot. Dissolve the alun, add clean and completely wet wool, and heat it to about 90C for an hour. Then, I always just let it cool off in the solution until the next day
  • One 10 g test skein of wool, mordanted by leaving it in a cold 10% solution of alun for 24 hours.

Both skeins then went into the same dye bath in order to compare them directly. The dye bath consisted of 40 g of dried heather from last fall, I had wanted to try that for the longest time, to see if heather yellow is warm or cold. And the result:


I am not able to tell the skeins apart, so the conclusion is that cold mordanting us just as good as hot. I think this is great news, because it really saves electricity!

The heater’s yellow is a wonderful warm tone, so I will definitely collect more this fall. Next time I dye with heather, though, it should be boiled and the dye bath strained before the wool goes in. The heather twigs are very difficult to remove – they are like small hooks inserted in the yarn.


Mordant 10% alun hot or cold

Water Tap

Yarn Supersoft 575 m/100 g

Yarn:Dyestuff ratio dry 1:2

Conclusion Heating is not necessary for alun mordanting! 

Heather yellow is warm and wonderful

Possible improvements Remove heather twigs before adding yarn

De to nøgler garn ovenover er begge bejset med alun, men det ene uden nogen form for opvarmning. Det ser ud til at virke fuldstændig ens – en god nyhed, for det betyder en stor energibesparelse under naturfarvning. Nøglerne er farved med lyng fra sidste sensommer.