Actually wool is difficult to dye black with natural dyes! The best bet is to start with logwood.
From a workshop I led some time ago ( 2006) I have some examples of logwood that are violet, very dark brown and the elusive black depending on which additive was used on the mordanted wool that was dyed with logwood. It must have worked once and the samples in my Dyeing Folder are still fast.
So now to repeat this and try and get enough for a decent sized skein.
So this is stage three, 10% powdered logwood was used for the dye bath and after dyeing the yarn was left overnight to cool in the dye bath.
Reference in 'the Dyers Assistant' James Haigh 1800 has a recipe with logwood, but he appears to use elder, sumach and soda, along with much copperas after the initial mordanting. My previous sample just used copperas as the additive to get black. Fingers crossed it will work 10 years on too. Soda tends to rot wool so best to avoid this if possible.
The finished skeins - black. They really are black - difficult to get a black in the image, apologies I am just using my ipad for the photos!
Some of these are off to Lucy for the History Wardrobe (www.historywardrobe.com) and many thanks Lucy for the historical information & motivation to dye with logwood again.