Yes, I know it's midsummer and I haven't written a thing about what I've been dyeing. My latest dyeing mania is a somewhat lengthier process than usual - but it's Amazing. Fermentation Dyeing.
There is not as much information as I'd wish about plant fermentation dyeing, but from what I gather the method was salvaged from history by Anne Rieger in the south of France. The process begins by fermenting plant matter in water for a week or more, releasing the gas and stirring the contents daily. After straining, the dye is separated into two vats. Lemon juice is used to lower the pH of one vat to 4, while wood ash water raises the pH of the other to 11. Protein fibers are steeped in the acidic bath, dried out of the sun, and then submerged in the basic bath. And just like that, you have lightfast color with no heat and no mordants. The colors are beautiful, and the wool samples I've dyed have the most wonderfully soft hand. Cellulose fibers also seem to take the color when given a longer steeping period, but not as strongly. Some inspiration can be found at Riihivilla and Shades of Lynx, and check out the samples I've been working up below.
above, from left: basic dahlia, acidic dahlia; basic cherry leaf, acidic cherry leaf
above, clockwise from upper left: acidic elderberry, acidic dahlia, basic dahlia, basic elderberry
cherry leaf and twig