Dye Plants II: The Atlantic Purple Wonder Archil lichen Roccella tinctoria

Rocella tinctoria
Rocella tinctoria
Detail on Archil lichen (Roccella tinctoria)
Detail on Archil lichen (Roccella tinctoria)
A closer look on the lichen Rocella fuciformis
A closer look on the lichen Rocella fuciformis

The Ancient Red from Archil Lichen

Orchella weed or archil lichen is a grayish green lichenized fungus Roccella tinctoria. Archil lichen is an ancient source of a natural red-violet dye known to man. Its use in dyeing is very old and possibly dates back to the Mesopotamian civilization. According to Theophrastus, Greek philosopher and naturalist (371-287 BC.), the red dye extracted from the archil lichen, Roccella tinctoria, was more beautiful than the purple, the most valuable colour and often synonym of high social status for whoever wore it. This "dye plant" is in reality a fungus living in a long lasting symbiotic relationship with a, a green alga. The composite organism is known as lichen where the fungus, the dominant partner, is called the mycobiont and the photosynthetic partner is called the photobiont or phycobiont. Lichens are very diverse in form and nature as the fungus can “marry” one or even three different species of algae simultaneously. Technically lichens are named after the fungus.

The hair-like and branched archil lichen Roccella tinctoria, of thefamily Roccellaceae, is common to rocks, boulders and cliffs on the sea sore mostly and on trees along sea-coasts. From early on it was reported in the first Atlantic voyages of the fifteen century. From that time and until the 1850s it was collected in rocks and boulders in the Atlantic archipelagos, particularly in the Azores, Madeira, Canary Islands and Cape Verde, and in some coastal areas of Brazil. Its economic exploitation was of such importance that its production in the Azores islands was exclusively under the Portuguese Crown monopoly. Severe penalties were thus destined for those who smuggled it. In fact, in the early history of the Azores, the dye extracted from archil lichen, Roccella tinctoria, and from other Roccella species, most notably Roccella fecifornzis, was one of the most important export products of the islands and was thus a very important source of income for Azorean families, reaching its apogee in the sixteenth century. In fact, in some cases it was even the reason for the establishment of settlements in remote places in some islands as its Portuguese popular name urzela is the basis for naming many places still existing today in the Atlantic islands, like the parish of Urzelina in the island of São Jorge, in Azores. Urzela is also use to name other species of lichens of the genus Roccella from which other similar dyers are extracted. Also, the English terms archil and orchella come from the Middle English orchell that derives from the French orseille which in turn as its origin in the Portuguese urzela.

Urzelina, in Azorean island of São Jorge
Urzelina, in Azorean island of São Jorge
Millstone used to grinde archil lichen in Azores.
Millstone used to grinde archil lichen in Azores. | Source
Rocella fuciformis, another species of Rocella lichens widely used as a source of natural dyes.
Rocella fuciformis, another species of Rocella lichens widely used as a source of natural dyes. | Source

In Cape Verde, where the archil lichen Roccella tinctoria grows in altitude mostly its collection was also an important activity that lasted until the nineteenth century, enabling human livelihood in times of severe famine caused by drought that often occurred. However, due to its natural habitat, collecting Roccella tinctoria was often a very painful and risky activity that required climbing cliffs and escarpments of difficult access. Therefore, serious injuries and even death were not uncommon in the many falls that occurred. Due to its high value, the geographic range of Roccella tinctoria was greatly enlarged since its economic exploitation initiated by the Portuguese in the Atlantic archipelagos in fifteen century began. Today, Roccella tinctoria can be found in the Canary Islands, Madeira, Morocco and West African coast down to South Africa, Brazil and the west coast of South America, and in the Malabar Coast of India. The methods and techniques for producing the red dye from Roccella tinctoria were very well kept secret by Flemish weavers for many decades. Archil lichen was thus imported as raw material from the Atlantic archipelagos (Azores, Madeira, Canaries and Cape Verde) and coastal areas of Brazil and Southwest Africa, keeping trade routs that started in early fifteenth century and remained active until the 1850s when the importance of natural dyes succumbed to their chemical synthesis.

The Azores

Cells stained with orcein.
Cells stained with orcein.
The popular litmus paper for measuring pH.
The popular litmus paper for measuring pH.

Extraction and Dyeing Processes

The reddish-brown dye orcein was prepared by placing archil lichens for two days in solutions of ammonia (traditionally urine was used as a source of ammonia), mixed with potassium carbonate, calcium hydroxide, or calcium sulfate (in the form of potash, lime, and gypsum) and left to ferment for six weeks. In the process, lecanoric acid is obtained which is then converted, after oxidation, to orcein. Orcein can also be obtained from other species of lichens from genera Rocella, Lecanora, Umbflicaria, Parntelia, but in practice the two most valuable sources were Rocella tinctoria and Rocella fecifornzis commonly known as orchella weeds.

Orcein was used to dye wool and silk directly in shades of red, brown and blue to violet. Red was obtained by treating orcein with tin salts, used as mordant, while violet was obtained from treatment with alum. Its popularity was such that it was used as a cheap substitute of purple in ancient Rome and remained of great value for dyeing textiles until its replacement by synthetic dyes. Today, orcein and litmus blue (its blue form) continue to have wide application that goes far beyond its traditional use in the textile industry. It is used in microscopy, as a contrast stain, and is also more commonly known as a pH indicator used for example in the indicator paper, the litmus test. It can also be used as food dye, however orcein is toxic and therefore its use is banned in the European Union. However, it is used in the USA to colour the skin of oranges.

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