Some of the best blacks and neutrals of the painter are those formed with colours of sufficient power and transparency upon the palette. Prussian blue and burnt lake afford a powerful though not very durable black; and compound blacks in which transparent pigments are employed will generally go deeper and harmonize better with other colours than any original black pigment alone. Hence lakes and deep blues, added to the common blacks, greatly increase their clearness and intensity: in mixture and glazing of the fine blacks of some old pictures, ultramarine has evidently been used. In this view, black altogether compounded of blue with red and yellow, each deep and transparent, and duly subordinated according to its powers, will give the most powerful and transparent blacks; although, like most other blacks, they dry badly in oil. Of course, as with all compound colours, it depends entirely on the pigments employed whether these mixed blacks are permanent or not: a compound black can very well pass through the stages of black to grey, gray, or dirty white, if each link in the chain of combination be not as strong as its fellows. * * * * * 296. _Black Chalk_ is an indurated clay, of the texture of white chalk, and chiefly used for cutting into crayons. Fine specimens have been found near Bantry in Ireland, and in Wales, but the Italian has the most reputation. Crayons for sketching and drawing are also artificially prepared, which are deeper in colour and free from grit. Wood charcoal is likewise cut into crayons, that of soft woods, such as lime, poplar, &c., being best adapted for the purpose. 297. _Black Ochre_, Earth Black, or Prussian Black, is a native earth, combined with iron and alluvial clay. It is found in most countries, and should be washed and exposed to the atmosphere before being employed. Sea-coal, and other black mineral substances, have been and may be used as substitutes for the more perfect blacks, when the latter are not procurable, which now seldom or never happens. 298. _Bone Black_, obtained by charring, is similar to that of ivory, except that it is a little warmer in tone, having a reddish or orange tinge, and is a worse drier in oil. Like ivory black, it is very transparent. Immense quantities of bone black are consumed with sulphuric acid in the manufacture of shoe blacking. 299. _Coffee Black_,