Orcein is a purple pigment that can be isolated from a range of lichens, here I’m collecting ochrolechia tartarea ( I think), they can be very hard to identify!The lichen needs to be soaked in ammonia for 4 months, this was probably done in large vats and the pigment used for a range of purposes, the quantity needed for manuscript illumination is tiny.After about 10 weeks a colour change should be occurring, if not you’ve got the wrong lichen!On week 16 a bright purple liquid can be poured off, it can be used directly on parchment as in the Book of Kells for the red wine coloured areas or mixed with gypsum to produce a bright purple. By adding acid the colour can be made more pink and alkalis deepen the violet tones, the range of tones in the Lindisfarne Gospels suggest that this technique was understood by Aedfrith at least. The ‘R’s here have been coloured with orcein and gypsum, the ‘A’ and ‘B’ with vinegar added to the mix
