Dyeing Purple with Lichen — The Orchil Fermentation Vat

Not all lichens produce dye. The orchil-producing species belong to specific genera: Umbilicaria (rock tripes — large, leathery, brown discs on rocks), Lasallia (similar to Umbilicaria), Ochrolechia (crust lichens that turn red when scratched), and Roccella (coastal rock lichens). To test a lichen, place a small fragment on a white plate, add a drop of household ammonia, and wait 10 minutes. If the spot turns pink or red, the lichen contains orchil precursors. Collect sustainably — lichens grow extremely slowly (1-2 mm per year), so take only what you need and leave the majority undisturbed.

Rinse the lichen briefly in cold water to remove dirt, bark, and debris. Do not soak — you do not want to wash away the dye precursors. Chop or tear the lichen into small pieces roughly 1 cm across. Smaller pieces expose more surface area to the ammonia, accelerating the fermentation. For Umbilicaria, tear the leathery discs into strips. For crust lichens, crumble them by hand.

Place the chopped lichen in a wide-mouthed glass jar (1-2 litre capacity). Add enough liquid to just cover the lichen — either stale urine (7+ days old, strongly ammoniacal) or a solution of 1 part household ammonia to 2 parts water. The ammonia provides the alkaline environment needed to convert the lichen's depsides into orcein. Stir to mix, then cover the jar loosely — fermentation gases need to escape. The liquid should be about 2 cm above the lichen.

Place the jar in a warm location (20-30°C) and stir once daily for 3-6 weeks. The colour will evolve: day 1-3, brown-grey; week 1, pink-rose; week 2-3, magenta-red; week 4-6, deep violet-purple. The ammonia smell will be strong — work outdoors or in a well-ventilated space. The daily stirring introduces oxygen, which is needed for the orcein to form (unlike indigo, orchil requires oxidation). When the paste is a deep, rich purple and the liquid is intensely coloured, the fermentation is complete.

Strain the fermented paste through muslin or a fine mesh strainer into the dye pot, squeezing the lichen pulp to extract all the purple liquid. The strained dye liquor should be a deep, rich violet — one of the most beautiful colours in natural dyeing. Add enough warm water to make about 4 litres total (enough to cover 100 g of wool). The spent lichen pulp has given up most of its colour but can be composted.

Orchil dye does not require a mordant — the orcein bonds directly to protein fibres. Pre-wet the wool in warm water, squeeze out excess, and lower it into the dye bath at room temperature. Slowly raise to 70-80°C (slightly lower than other natural dyes — high heat can dull orchil colours) and hold for 45 minutes. Turn the wool gently every 10 minutes. The wool will absorb the purple readily.

Turn off the heat, let the wool cool in the bath for several hours, then rinse in lukewarm water until the runoff is mostly clear. The final colour ranges from soft lavender (low lichen concentration) to deep warm purple (high concentration with long fermentation). Orchil purple has a characteristic warmth — it leans red-violet rather than blue-violet, distinguishing it from logwood and indigo-based purples. Dry in shade — orchil is moderately lightfast but fades faster in direct sunlight than indigo or cochineal.

Orchil was the accessible purple — affordable where Tyrian purple was ruinously expensive. A jar of lichens and urine cost nothing; murex purple required thousands of sea snails. The colours overlapped enough that orchil was regularly used to counterfeit Tyrian purple, and sumptuary laws in some medieval cities specifically banned the practice. Orchil's modern legacy lives on in every chemistry classroom: litmus paper, the universal pH indicator, is made from orcein extracted from Roccella lichens. The same chemistry that dyes wool purple also changes colour in response to acids and bases — a connection between textile craft and laboratory science that spans two millennia.