This is a great one to do with the kids. My two and four year old did most of the work. Waiting for the wool to 'cook' was the hardest part! And they were thrilled with the results.
wind the wool off the ball into a loose skein
peel the skins off some brown onions and place in an alluminium pot
I found that using an alluminium pot was a reasonable substitute for mordent, as I didn't want to use any chemicals with the kids.
wet the wool until it is soaking wet
put wool in pot with onion skins and fill with water until covered
The actual amount of water is not important.
simmer - but do not boil for up to three hours
Do not aggitate the wool or it may become matted.
pull wool out of pot and drain - then hang it up somewhere out of the sun to dry.
The ratio of skins to wool and the amount of time the brew is left to simmer will both impact on the depth of the final colour. We used 6 medium onions to 50g of white wool.
The fact that it changed colour at all was enough for my kids to be delighted!