Joan Moshimer, an American icon of rug hooking, once provided the following directions for onion skin dyeing.
"Gather together an assortment of colored flannels, new or used, in all sorts of odd sized pieces. The colors can be red, rose, orange, tan, greens, blues, grays, lavenders and some small checks and tweeds if you have them. Darker colors will result if you start with a lot of dark colored wools. Generally, for the best results, use medium and light colored wools. Soak wool for a few minutes in warm water with a little detergent in it, then arrange the wool in layers in a medium size enamel pan, putting between each layer a handful of the onion skins and about one tablespoon of uniodized salt. Let these layers build up to within a few inches of the top of pan then cover with boiling water. Let it all simmer for about 30 minutes, then rinse well and dry. The colors that emerge will be like no others you have evern seen, soft and subtly blended with a golden glow from the onion skins. The more onion skins you use, the more pronounced will be the 'glow'."