Plumbago, or Graphite, contains in spite of its name no lead, being simply a species of carbon or charcoal. In most specimens iron is present, varying in quantity from a mere trace up to five per cent, together with silica and alumina. Sometimes manganese and titanic acid are likewise found. It is curious that carbon should occur in two distinct and very dissimilar forms—as diamond, and as graphite; one, white, hard, and transparent; the other, black, soft, and opaque: the artist, therefore, who uses a pigment of plumbago, paints with nothing more or less than a black diamond. The best graphite, the finest and most valuable for pencils, is yielded by the mine of Borrowdale, at the west end of Derwent Lake, in Cumberland, where it was first wrought during the reign of Elizabeth. A kind of irregular vein traverses the ancient slate-beds of that district, furnishing the carbon of an iron-grey colour, metallic lustre, and soft and greasy to the touch. Universally employed in the form of crayons, &c. in sketching, designing, and drawing, until of late years it was not acknowledged as a pigment: yet its powers in this respect claim a place for it. As a water-colour, levigated in gum in the usual manner, it may be effectively used with rapidity and freedom in the shading and finishing of pencil drawings, or as a substitute therein for Indian ink. Even in oil it may be employed occasionally, as it possesses remarkably the property of covering, forms very pure grey, dries quickly, injures no colour chemically, and endures for ever. These qualities render it the most eligible black for adding to white in minute quantity to preserve the neutrality of its tint.

Although plumbago has usurped the name of Black Lead, there is another substance more properly entitled to this appellation, and which may be used in the same way, and with like effects as a pigment. This substance is the sulphide of lead, found native in the beautiful lead ore, or Galena, of Derbyshire. An artificial sulphide can be prepared by dry and wet processes, which is subject to gradual oxidation on exposure to the air, and consequent conversion into grey or white. Neither variety can be compared to graphite for permanence, although the native is preferable to the artificial.

Plumbago, or the so-called Black Lead, is often adulterated to an enormous extent with lamp black.

290. BLUE BLACK,

Charcoal, Liege, or Vine Black, is a well-burnt and levigated charcoal prepared from vine twigs, of weaker body than ivory or lamp black, and consequently better suited to the grays and general mixed tints of landscape painting, in which it is not so likely to look black and sooty as the others may do. Of a cool neutral tint, it has, in common with all carbonaceous blacks, a preserving influence on white when duly mixed therewith; which it owes, chemically, to the bleaching power of carbon, and, chromatically, to the neutralizing and contrasting power of black with white. Compounded slightly with blue black, and washed over with zinc white, white lead may be exposed to any ordinary impure atmosphere with comparative impunity. It would be well for art if carbon had a like power upon the colour of oils, but of this it is deficient; and although chlorine destroys their colour temporarily, they re-acquire it at no very distant period.

Alone, blue black is useful as a cool shade for white draperies; and compounded with cobalt, affords a good gray for louring clouds.

291. BRITISH INK

is a compound black, preferred by some artists to Indian ink, on account of its not being liable to wash streaky, as the latter does: at the same time it is not so perfectly fixed on the paper as Indian ink.

292. INDIAN INK,

sometimes called China or Chinese Ink, is chiefly brought from China in oblong cakes, of a musky scent, ready prepared for painting in water. Varying considerably in body and colour, the best has a shining black fracture, is finely compact, and homogeneous when rubbed with water, in which, when largely diluted, it yields no precipitate. Without the least appearance of particles, its dry surface is covered with a pellicle of a metallic appearance. When dry on the paper, it resists the action of water, yet it will give way at once to that action, when it has been used and dried on marble or ivory, a fact which proves that the alummed paper forms a strong combination with the ink; possibly a compound of the latter on an aluminous base, might even be employed in oil. Different accounts are given of the mode of making this ink, the principal substance or colouring matter of which is a smoke black, having all the properties of our lamp black; the variety of its hues and texture seeming wholly to depend on the degree of burning and levigating it receives. From certain Chinese documents, we learn that the ink of Nan-king is the most esteemed; and among the many sorts imported into this country, we find those of the best quality are prepared with lamp black of the oil of Sesame; with which are combined camphor, and the juice of a plant named Houng hoa to give it brightness of tone. According to an analysis by M. Proust, the better kinds contain about two per cent. of camphor. By some, the pigment known as Sepia has been supposed to enter into their composition.