Orcein is a naturally occuring pigment that can be found in several British lichen species. It was one of only 2 sources of purple in ancient times and has been proven to be the pigment used in the Book of Kells.
This is Ochrolechia Tartarea, its fairly common on the Black Isle and I only need a small amount, about half a small jam jar full. This lichen appears to occur in two forms together, one covered with small discs, the other without, it's only the stuff without discs that I've got to work.
All you need is patience and ammonia, A solution of half ammonia and half water to just cover the lichen, put the lid on and shake vigorously for 10 minutes. Then let it ferment for 16 weeks shaking every few days and the liquid is ready to use as ink with no further preparation or binder. It looks exactly like the Kells purple on vellum.