Here are the samples after around 10 days of sitting on a windowsill – and some of those days were actually very sunny! ^_^
fibres without any modifiers
vinegar modified fibres at the top, at the bottom modified with washing soda
while wool faded rapidly, silks, linen and bamboo/ramie have almost retained the original color
sun exposed fibres while wet on the left – the least color loss of all samples
fibres used to exhaust dyebath on the right
As you can see a lot of color is gone. I haven’t seen a natural dye fading so rapidly. While it is rather washfast the lightfastness is very poor. In most of the books, in fact in all I have on nat dyeing authors mention the colours one can get from this lichen as well as the fact that it is a substantive dye, yet no one talks about fastness, except one, which I came across only two days ago. It is a book by Rita J. Adrosko, Natural Dyes and Home Dyeing from 1971. She mentions another dyestuff, Orchil and cites an American dyer who wrote in 1869: “It is seldom used by itself for dyeing, but usually to help or top other colors; when used alone it gives colors which are very loose in air, fading almost visibly in sunglight…” I feel the same applies to Xanthoria Parietina. So the mystery is solved. It’s been interesting to try this lichen but there are certainly easier ways – how to ge a good grey color :)!