Just to keep this thread alive and as a further example of just how confusing the subject of dyes can be, have a look at this.
MacAlistair tartan - Wilsons' Colours
MacAlistair tartan - Old (Ancient or Vegetable Dye) Colours
Same sett but in different shades, apparently....
But look what a year in direct sunlight does.
Even with modern chemical dyes some shades fade more than others. It's interesting that the dark blue has retained its depth the best, something one sees with traditional natural dyes too. The red on the other hand has faded quite a lot whereas a traditional naturally dyed cochineal red is pretty light fast too if fixed with a tin mordant.
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