A blue pigment, which reddens when dipped into acids.
A purple dye obtained from certain lichens; known also as turnsole.
A blue stain from lichens, turned red by acids.
The coloring matter obtained from the species of Rocella, Variolaria, Leconora, and similar lichens. It is used chiefly as a test for acids and alkalis, being colored red by the former and restored to its original color by the latter.
n. [German] A purple dye obtained from a lichen, and firom a kind of spruge common in the south of Europe— it turns blue with alkalies and red with acids.