Information as to the dyeing properties of certain lichens is given in most of the books or papers dealing with these plants from the herbals onwards. Hoffmann[1296] devoted a large part of his Commentatio de vario Lichenum usu to the dye-lichens, and, illustrating his work, are a series of small rectangular coloured blocks representing samples of woollen cloth dyed with different lichens. There are seventy-seven of these samples with the colour names used by French dyers.
An important treatise on the subject translated into French was also contributed by Westring[1297]. He desired to draw attention to the tinctorial properties of lichens other than the Roccellae which do not grow in Sweden. The Swedes, he states, already used four to six lichens as dye-plants, but only for one colour. He demonstrated by his improved methods that other colours and of finer tint could be obtained. He describes the best methods both of extraction and of dyeing, and then follows with an account of the different lichens likely to be of service. The treatise was subsequently published at greater length in Swedish[1298] with twenty-four very fine coloured illustrations of the lichens used, and with sample blocks of the colours to be obtained.
b. The Orchil Lichen, Roccella. The value of Roccella as a dye-plant had been lost sight of until it was accidentally rediscovered, early in the fourteenth century, by a Florentine merchant called Federigo. He introduced its use into Florence, and as he retained the industry in his own hands he made a large fortune, and founded the family of the Orcellarii, called later the Rucellarii or Rucellai, hence the botanical name, Roccella. The product was called orseille for which the English name is orchil or archil. Another origin suggested for orchil is the Spanish name of the plant, Orcigilia. There are a number of different species that vary in the amount of dye-product. Most of them grow on rocks by the sea-side in crowded bluish-grey or whitish tufts of strap-shaped or rounded stiff narrow fronds varying in length up to about six inches or more. The main supply of “weeds” came from the Levant until the fifteenth century when supplies were obtained from the Canaries (long considered to produce the best varieties), Cape Verd and the African coasts. The geographical distribution of the Roccellae is very wide: they grow on warm sea-coasts all over the globe, more particularly in Angola, the Cape, Mozambique, Madagascar, in Asia, in Australia, and in Chili and Peru.
Zopf[1299] has proved the existence of two different colouring substances among the Roccellas: in R. fuciformis ([Fig. 57]) and R. fucoides (both British species), in R. Montagnei and R. peruensis the acid present is erythrin; in R. tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In R. tinctoria ([Fig. 133]), according to Ronceray[1300], the acid is located chiefly in the gonidial layer and the soredia but is absent from the cortex and centre. In R. portentosa it is abundant in the cortex and central layer, while scarcely to be detected in the gonidial layer, and it is wanting altogether in the soredia. In R. Montagnei it is chiefly found in the cortex and the gonidial layer, and is absent from the soredia and from the medulla.
c. Purple Dyes: Orchil, Cudbear and Litmus. Orseille or orchil is formed not only from erythrin and lecanoric acid (orseillic acid), but also from erythrinic, gyrophoric, evernic and ramalic acids[1301] and may be obtained from any lichen containing these substances. By the action of ammonia the acids are split up into orcin and carbonic acid. In time, under the influence of ammonia and the oxygen of the air[1302], orcin becomes orcein which is the colouring principle of orchil; the perfecting of the process may take a month. The dye is used for animal fibres such as wool and silk; it has no effect on cotton.
There are several different preparations on the market, chiefly obtained from France and Holland; orchil or orseille in the form of a solution, cudbear (persio of Germany) almost the same, but manufactured into a violet-reddish powder, and litmus (tournesol of France) which is prepared in a slightly different manner. At one time the lichen, broken into small pieces, was soaked in urine; a fermentation process was set up, then lime and potash with an admixture of alum were added. The mass of material when ready was pressed into cubes and dried in the air. Commercial litmus contains three substances, erythrolein, erythrolitmin and azolitmin; the last named, which is the true litmus, is a dark brown amorphous powder soluble in water, and forming a blue solution with alkalies.
Fig. 133. Roccella tintoria Ach. From the Cape of Good Hope.
An aqueous solution of litmus when exactly neutralized by an acid is violet coloured; it becomes red with the smallest trace of free acid, or blue with free alkali. Litmus paper is prepared by steeping specially prepared unsized paper in the dye solution. It is as a ready and sensitive indicator of acidity or alkalinity that litmus is of so much value. According to Zopf[1303] it is also used as a blueing agent in washing and as a colouring of wine. Litmus is chiefly manufactured in Holland. Still another substance somewhat differently prepared from the same lichens is sold as French purple, a more brilliant and durable colour than orchil.