|Common names of dyes:||Orchil, archil, orseille (French) and cudbear; generic terms used for red/purple/violet dyes obtained by treatment of certain lichen species with ammonia.|
|Raw material source:||Collection of wild growing material from trees and rocks.|
|Common names of lichen sources:||
|Botanical sources:||(a) Orchil/cudbear types: Rocella tinctoria, Ochrolechia tartarea (syn. Lecanora tartarea), Evarina prunastri (Stag's horn), plus some species of Parmelia, Umbilicaria and Lasallia. (b) Non-orchil types include certain species of Parmelia, Hypogymnia, Lobaria, Peltigaria, Sticta and Xanthoria.|
|Distribution:||Worldwide; certain orchil types common in coastal sub-tropics and tropics.|
|World production and international trade:||Unknown.|
|Availability of reliable published information:||Poor.|
Lichens are a unique group of plant organisms in which there is a symbiotic association between an alga and a fungus. They are very slow growing, occur on rocks and trees and are remarkable in their geographical distribution which spans the tropics to the Arctic tundra. Approximately 15,000 different types of lichens have been recognized, of which the majority occur in habitats which are too austere for other plants.
Man has employed certain types of lichens from ancient times for purposes which include food, animal fodder, medicinal preparations, perfumery and as dyestuffs.
With wool and silk, the lichen dyes can be employed without a mordant and produce subtle, muted colours which range from yellow, brown, red, purple to violet. Certain species, known as the orchils, provide purple to red-violet dyes on treatment with ammonia. This same group is employed also to produce the acid-base indicator, litmus.
The chemistry of the lichen pigments is complex, involving a diversity of oxygen ring compounds which are generically, if inaccurately, termed the "lichen acids". Orchil type dyes and litmus contain a mixture of derivatives of the natural depside pigments, produced by the action of the ammoniacal liquor. The process involves conversion of depsides to orcinol and then to orcein; the latter being a mixture of oxy- and amino-phenoxazon or phenoxazin.
The purple orchils have been the most important group of lichen dyes in historical trade and during the classical Greek and Roman period production was probably based on Rocella tinctoria which is native to the Mediterranean area. During the seventeenth century, a growth in usage of orchils developed with the discovery of the ammonia treatment process. Shortages of supplies developed in the Mediterranean and new sources were developed first in the Canary Islands and on Cape Verde. During the nineteenth century, India and Ceylon (Sri Lanka) assumed importance with processing mainly being done in the United Kingdom. Later, supplementation of supplies developed in Northern Europe and in the USA.
During the twentieth century, usage of lichen dyes of all types has declined in the face of competition from lower cost and progressively improving synthetic dyestuffs. However, lichen dyes resisted supplantation for a much longer period than most other natural dyestuffs, especially in materials such as Scottish and Irish tweeds.
In recent years, there has been a revival in usage in lichen dyes of
local origin in the manufacture of specialist, craft textiles in Europe
and North America where the subtlety of the colour is much appreciated.
Nevertheless, no prospects are foreseen for any significant global improvement
in the low level of international trade.
This is a simple operation of collecting the appropriate species for particular applications, followed by drying and storage until required for processing.
The basic method for non-orchil dye preparation is to gently boil the lichen in soft water for several hours. Depending upon the lichen type and the desired colour, the pH may be altered by addition of vinegar or washing soda.
This process involves a slow aerobic fermentation of the lichen in aqueous ammonia over a period of a couple of weeks.
A mixture of the most common orchil type lichens (Rocella, Lecanora/Ochrolechia
species) are employed for litmus production. The process is a variation
on the orchil dye method and involves addition of potash and lime to the
aqueous ammonia medium.
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BOLTON, E. (1960). Lichens for Vegetable Dyeing. Newton Centre, Mass., USA: Charles T. Branford Co.
CASSELMAN, K.L. (1986). Colour magic from lichen dyebaths. Shuttle, Spindle and Dyepot, 17(2), 74-78. (West Hartford, Conn., USA: Handweavers Guild of America).
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HALE, M.E. (1983). The Biology of Lichens. London: Edward Arnold.
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