Tried the cabbage recipe again, wanted to see what different mordants would do. Shredded a full purple cabbage and boiled for about 20 min in 2l of water. I think it could take more cooking, there was still color left in the cabbage. Drained the liquid, divided into 4 jars, to try iron, vinegar, alum and baking soda. Final result:
Here are the eggs after about an hour in the dyes:
So, I recommend alum. Vinegar and soda didn’t work very well for me, however, I used tap water, and it’s full of chlorine here, which might affect the dyes, can’t really be called a pure experiment. Use demineralized or distilled water if you want to make your experiment really “scientific”, and let me know how it goes.
The iron was OK, gave a decent gray after an hour and almost black after a night, but I wouldn’t use cabbage for that, unless you don’t have other options and don’t mind the cabbage smell.