I have long last concluded my first test of using rhubarb leaves as mordant instead of chemical ones. (even though they are in fact toxic, they are natural. Or, as MotherOwl points out below, even though they are natural, they are in fact toxic!)
And I have to say, it’s not really worth the effort. Not only does it not help the wool take up the dye any more than an unmordanted skein, in fact sometimes I could hardly see the difference. It also doesn’t add to lightfastness, both of which are the whole point of mordanting in the first place.
I tried both wool and cotton and none had better results than the other for me.
Top to bottom and left to right: Alum + rhubarb simmer not boil, boiled rhubarb + iron, boiled rhubarb, rhubarb + madder, rhubarb + weld, rhubarb + french marigold.
The alum mordanted, rhubarb dyed skein was also a handsome yellow in itself for sure, although it has faded a bit in just a month even without light. Without mordant they are a varying shade of beige depending on how hard you heat the dyebath. The madder is also quite alright, although not any kind of red exactly.
It did have one redeeming feature though: I really liked the shade I got from overdyeing with woad. From historical textiles we can see that some yellows fade away, leaving a once green section of fabric blue, but I’m not really expecting anything I make to live for 600 years. I’ll be forgotten and the line will die out when I do. It’s a patchy dye job because the vat had too little water and too much yarn, so I believe the darkest strands are the “truest” had it been done properly.
Check also under comments in my first post for additional info.
Ikke den helt store gevinst efter min mening, hvilket vi også debatterede under foregående indlæg. Garnet bliver ikke lysægte eller optager farve i samme grad som med alun, de gule farver kan knap nok ses ovenpå selve rabarberfarven som bliver mørk beige hvis man koger den. Det brunlige garn på billedet er krap, og den er vel ok, den grønne er overfarvet med vaid, og blev ret god, bortset fra jeg havde for lidt vand i gryden, så den er lidt skjoldet.