The coal tar colours have nearly superseded those from lichens which incrust rocks, walls and stems of aged trees with brilliant colours, which do not however furnish dyes directly; they yield a colourless crystalline substance which combines with alkalies to furnish very beautiful dyes; it is exactly the opposite of rosaniline, which is a base. The Variolaria dealbata yields litmus or orchil, from which the beautiful French purple is made. The Rocella tinctoria and fusiformis give blue and purple, and the pale yellow lichen, Parmelia parcolerina furnishes a bright yellow dye, which a little ammonia changes to a rich red, inclining to purple. Mauve was first made from orchil, but was not permanent. The fine dyes, alizarine blue, Turkey red and garancine, are still much in use. They are derived from madder, the dried roots of the Rubia tinctorum; the madder dyes most extensively employed are alizarine and flower of madder. Mauve and other dyes are derived from guano, the offal of seabirds, which is imported in large quantities for manure. The coal tar colours are manufactured on a highly scientific plan and most extensive scale in Great Britain, to supply the enormous quantity annually consumed in dyeing silk and printing cotton. In general, animal substances such as silk and wool can be permanently dyed at once, because they have a strong affinity or attraction for coloured dyes. If silk is destined to be a moiré, the silk before it is woven undergoes a chemical process in order to introduce fatty matter into it which gives a softness to the silk when woven and renders it fit to receive the moiré by intense pressure.