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I. Charcoal Blacks.

Most of the blacks of this class, besides their incorrup-tibility, have the advantage of a full colour, and workfreely in all the forms in which powdery pigments areapplied provided they have been carefully prepared, bythoroughly burning the subject in a close vessel, and after-wards grinding the coal into a powder of due fineness.

Pieces of charcoal are used also in their entire state, fortracing the outlines of drawings, &c. in which intentionthey have an excellence, that their mark is easily wipedout. For these purposes, either the finer pieces of com-mon charcoal are picked out and cut to a proper shape;or the pencils are formed of wood, and afterwards burntinto charcoal, in a crucible, or other like vessel, coveredand luted. When the process is skilfully managed, thecoal retains exactly the figure of the wood : some havebeen so dextrous as to char an arrow, without alteringthe form even of the feather.

The artists commonly make choice of the smallerbranches of the tree, freed from the bark and the pith;and some particular kinds of wood, as the willow and thevine, they generally prefer to others. To discoverthe foundation of this preference, and how far the coalsof different vegetables differ from one another as colour-ing materials, I made the following experiments.

Small branches of the willow, vine, cherry, apple,pear, peach, plum, fig, birch, oak, elder, alder, yew, sloe,hazel, fir and pine trees, were thoroughly dried, and in-closed in a mass of luting, made of clay beaten up withsand and horse-dung :*• the mass, dried fiowly and gradu-ally heated to prevent its cracking, was kept red hotabout three hours. On carefully breaking it, the pieceswere all found well charred; but it could not be ob-served