colour. It requires no other preparation than that of being washed over, before it is used.—See Indigo.
8. Purple. The only simple colour or this kind at present, is colcothar of vitriol, or crocus martis. A beautiful purple lake may be prepared from logwood, by means of a solution of tin. As this mode of preparing colours is but little known, we shall give a few hints respecting it, under the subjoined head of Colouring Matter.
9. Brown. The chief Brown colours are bistre, and brown Pink.
Bistre is prepared from the most glossy, and perfectly burnt soot, pulverized, passed through a fine sieve; then baked in a little gum-water, and formed into cakes. This is a very useful colour in water, being exceedingly fine and durable, and not apt to spoil any other colours with which it is mixed. The brown-pink is said to consist of chalk, tinged with the colouring matter of fustic, heightened by fixed alkaline salts. It is, consequently, very perishable, and seldom used.—See also Chafer, vol. i. p. 486.
Colouring Matter is contained in almost every flower and root of vegetables, and may be extracted by a very simple process. The Dutch prepare pigments of the most beautiful shades, for instance, a very fine azure blue, from the blossoms of the corn blue-bottle, Centaurea Cyanus, L.—a delicate red, from the fresh leaves of roses, especially the small French rose;—an excellent violet from the flowers of that name, &c. in the following manner: Take the roots, leaves, or flowers of whatever quantity is desired, bruise them nearly to a pulp, put them into a glazed earthen vessel, pour a sufficient quantity of filtred water over them, and add a table spoonful of a strong solution of pure pot-ash to every pint of the former. Boil the whole over a moderate fire, till the liquor is evidently saturated with the colour afforded by the vegetable; then decant the fluid part, either through blotting paper, or cloth, and gradually drop into it a solution of alum, when the colouring matter will subside at the bottom. This powder should again be washed in several fresh waters, till they pass away perfectly tasteless: at length, it must be once more filtred through paper, and the remaining substance perfectly dried. From this preparation are afterwards manufactured the finest pigments, or water-colours, of the shops, by triturating them on marble stones, with the addition of a little clarified gum-water, and then forming them into cones, cakes, &c.
Having already, under the different heads of plants, mentioned the various purposes to which they may be usefully applied, in the arts of colouring, dyeing, tanning, &c. it would be superfluous to enumerate them on this occasion—a task we are necessarily oblige to defer, on account of the great variety of vegetables which will occur in the sequel of the alphabet. To enable, however, those readers who are engaged in any particular art, or trade, to take a comprehensive view of every useful fact connected with their respective pursuits, we take this opportunity of informing them, that we intend to give a copious and universal Index of Reference, at the conclusion of our labours. By the assistance of such an index, they will be enabled
