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.

Heather yellow is warm and wonderful

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