It was known to the ancient Greeks and Romans. But unlike other ancient dyes (indigo, Tyrian purple &c) the origin and chemical composition of the dye are less exact. 

These pages describe the history and chemistry of the dyes and give some of the classical recipes with extensive bibliographic references.

• archil
• orchil
• orcein
• litmus
• cudbear
• persio
• La Parelle
• La pourpre Français

The methods used to process the lichen to give purple dye are very similar: react it with ammonia (urine in former days) and air for a period of weeks.