Or _Quercitron Yellow_, is what its name implies. It is dark in substance, in grains of a glossy fracture, perfectly transparent, and when ground is of a beautiful yellow colour. In painting it follows, and adds richness and depth to, gamboge in water, and goes well into varnish; but any lead used in rendering oils siccative, browns it, and for the same reason it is useless in tints. 37. LEMON YELLOW, Or chromate of baryta, is exceedingly difficult to make well. Upon the mode of manufacture depend not only the beauty of the colour but its stability. If properly and carefully prepared, it is of a vivid lemon tint, deep or pale, very clear, very pure and permanent. It also washes well, and is entirely free from the slightest tinge of orange. This may be pronounced the only chromate which possesses durability, not being liable to change by damp or foul air, by the action of light or the steel palette-knife, or by mixture with white lead and other pigments, either in water or oil, in both of which it works pleasantly. Lemon yellow is chiefly adapted to points of high light, and has a peculiarly happy effect when glazed over greens in both modes of painting. In water it exceeds gamboge in brightness, and compounded therewith improves its beauty. This mixture also goes readily into oil; indeed it is the best and easiest way of rendering gamboge diffusible as an oil colour--simple emulsion of the gamboge in a little water, and trituration of the lemon yellow therewith, being all that is requisite for the purpose. Lemon yellow has not much power, and is semi-opaque. In distance, its light wash is used with great effect for cool sunny greens, for which a minute quantity of emerald green may be added to it. Being uninjured by lime, the colour is eligible in fresco and crayons. 38. MARS YELLOW, _Jaune de Mars_, _Jaune de Fer_, _Iron Yellow_, &c., is an artificially prepared iron ochre, of the nature of sienna earth. In its general qualities it resembles the ochres, with the same eligibilities and exceptions, but is more transparent, as well as purer, clearer, richer, and brighter. Like them it is quite permanent. The colours of iron exist in endless variety in nature, and are capable of the same variation by art, from sienna yellow, through orange and red, to a species of purple, brown, and black, among which are useful and valuable distinctions. They were formerly introduced by the author, and have been received under the names of Mars yellow, Mars orange, Mars red, Mars violet, and Mars brown. All of them are brighter and purer than native ochres, and equally stable. When carefully prepared, these pigments dry well in proportion to their depth, are marked by a subdued richness rather than brilliancy, and have the general habits of sienna earths and ochres. Their faint washes possess the desirable quality of transparent clearness.