We have a little (maybe not so little anymore) patch of Stinging Nettles (Urtica dioica) that I planted in the back yard years ago. Nettles are one of our favourite spring greens, and this is the time of the year when they’re at their best - tender, nutty and fragrant. (Later in the summer they become gritty and inedible.)
But this year’s crop has been particularly rapid-growing, and since we can’t eat that many, I thought I would try dyeing with them. They’re supposed to produce a green-grey, which is one of my favourite colours. I got advice from several books and websites, but the best all-around source seemed to be Rebecca Desnos. Following her advice, I simmered the plants (leaves, stems and all - even a few roots) very gently for a few hours, never allowing them to come anywhere near a boil. (She suggests that lower temperatures produce better colour.) Then I let them sit overnight and repeated the process again the next day.
Desnos recommends using an aluminum pot for brighter colour, but I don’t have one large enough to be of any use. I do have a large copper cauldron, though, which I thought might be better than stainless steel.
After the nettles had been simmering for five or six hours, I let them cool down again and strain out all the solid material. I used a couple of layers of very fine nylon net to filter out the tiny particles that gathered at the top of the liquid. Then with the plant material safely out of the pot, I brought it to a boil and reduced the volume a bit. Interestingly, when nettles are steamed or boiled for eating, they have a very distinctive and (I think) pleasant smell, but cooked at this lower temperature, they smelled very different. And not especially good. 
While the dye was cooking, I prepared the fabric by pre-treating it with soy milk. This is another Desnos favourite, and is often referred to as “soy milk mordant”, though it’s technically a pre-treatment rather than a mordant. Whatever. Many dyes work best on animal fibres like wool or silk, but plant fibres coated with soy milk take the dye more like wool than cotton. I thought I’d try it, since I was dyeing cotton.
I soaked the washed fabric in a tub of 50/50 water and unsweetened soy milk for a day, then removed the excess liquid in the spin cycle and hung it to dry. I repeated that twice more, to build up a better deposit of soy protein on the fibres.
Then the fabric was put into the hot nettle solution and simmered for a few hours before being allowed to cool and sit overnight. I stirred it regularly throughout, to keep the fabric from settling in any one position. The next day I put it through the spin cycle and hung the fabric to dry for three days before rinsing the dye out. (This is another Desnos suggestion, and she’s right - very little dye came out after letting it rest on the fabric that long.)
The final colour is a very pale green gray, just as promised. (Though in the photo it appears only slightly off-white.) It seemed a bit blotchy when it came out of the dye pot, but in fact it rinsed out with no irregularities in colour at all. I think I have enough to make a summer shirt out of this very light-weight cotton.
(Sorry all the photos are oriented sideways. Nothing I tried seemed to fix it. 
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