Went out to take a look at some massive colonies of Xanthoparmelia growing on a rock face. 5% potassium hydroxide test results in a nice deep yellow, almost green stain on the upper cortex. The medula is also K+, turning a deep blood red/orange. I blotted the soaked lichen on some paper and got this beautiful golden-rod ink. This ink was produced from less than a cm² of lichen and a couple drops of KOH. I would love to experiment more given the abundance of this lichen and the small amount of material needed to produce the ink. This photo was taken 24hrs after staining the paper but I’d need to further test the colour fastness.

Edit: I am conscious of ethical harvesting practices for lichens, I normally only harvest for identification purposes and even then I try to only collect samples detached from the substrate.