Editing Lichen (section)

=== Dyes ===
Many lichens produce secondary compounds, including [[Biological pigment|pigments]] that reduce harmful amounts of sunlight and powerful toxins that deter [[herbivore]]s or kill bacteria. These compounds are very useful for lichen identification, and have had economic importance as [[dye]]s such as [[cudbear]] or primitive [[antibiotics]].

A [[pH indicator]] (which can indicate acidic or basic substances) called [[litmus]] is a dye extracted from the lichen ''[[Roccella tinctoria]]'' ("dyer's weed")<ref>{{Cite web|title=A Modern Herbal {{!}} Litmus|url=https://www.botanical.com/botanical/mgmh/l/litmus35.html#med|access-date=2021-10-24|website=botanical.com}}</ref> by boiling.  It gives its name to the well-known [[Litmus test (chemistry)|litmus test]].

[[Traditional dyes of the Scottish Highlands]] for [[Harris tweed]] and other traditional cloths were made from lichens, including the orange ''[[Xanthoria parietina]]'' ("common orange lichen") and the grey foliaceous ''[[Parmelia saxatilis]]'' common on rocks and known colloquially as "crottle".

There are reports dating almost 2,000 years old of lichens being used to make purple and red dyes.<ref name=Casselman1999/> Of great historical and commercial significance are lichens belonging to the family ''[[Roccellaceae]]'', commonly called orchella weed or orchil. [[Orcein]] and other lichen dyes have largely been replaced by [[Dye#Natural and synthetic|synthetic versions]].