Ar'chil

Ar'chil, or ORCHIL (Fr. orseille; Span. archilla; Ital. orcello), is a colouring substance obtained from various species of lichens. The archil is not originally present in the lichens, but is developed during a process of putrefaction and fermentation. The lichens, collected from rocks near the sea, are cleaned, ground into a paste with water, placed in tanks, and ammoniacal liquids—such as purified gas liquor or stale urine—added; when, by the combined influence of the ammonia, air, water, and the constituents of the lichens, a violet-coloured matter is generated, which appears for a time to dissolve in the water, but finally falls to the bottom of the vat in the condition of a moist powder or paste. The latter is then mixed with some substance like chalk or stucco, to give it consistency. Archil is soluble in water and in alcohol, to either of which it imparts a violet colour with a good deal of a crimson hue. It contains orcein, which can be obtained as an amorphous red powder, and to which it owes its tinctorial power. It is much employed in the dyeing of silks; but though a brilliant lilac hue is imparted to the fabric, the colour is not a permanent one, being easily acted upon by the rays of the sun. Hence the cloth is first dyed lilac by another colouring matter, and is then passed through an archil dye, which imparts its brilliant hue. Archil is seldom employed to dye cottons, but it is often used, along with indigo, in the dyeing of woollen cloth. Cudbear (q.v.) and Litmus (q.v.) are analogous to archil, and are obtained from the same lichens. The lichens which yield the best archil in largest quantity are Roccella tinctoria and fuciformis. The former is called the Archil plant; it grows very sparingly on the south coast of England, but is obtained in large amount from the Canaries and Cape de Verd Islands, and from the Levant. It is of a substance between cartilaginous and leathery, roundish, pretty erect, branching in a dichotomous manner, of a grayish-brown colour, with powdery warts (soredia)—the apothecia (see LICHENS), orbicular, flat, horny, almost black. That from the Canary Isles is generally regarded as the best. It seldom exceeds the thickness of a pin, and is about an inch and a half in length. R. fuciformis now yields perhaps more of the Archil or Orchella weed of commerce than R. tinctoria. It differs from R. tinctoria chiefly in being not rounded, but flat, and in having the apothecia very distinctly bordered. It grows in similar situations, and is also a native of Britain, but is abundant only in warmer climates, as on the coasts of Africa, Madagascar, &c.