These colours are, however, obtained in many instances with best and most permanent effect, not by the intimate combination of pigments upon the palette, but by intermingling them, in the manner of nature, on the canvas, so as to produce the appearance at a proper distance of a uniform colour. Thus composed is the citrine colour of fruit and foliage, on inspecting which we distinctly trace the stipplings of orange and green, or of yellow, red, and green. The truth and beauty resulting from such stipplings in art may be seen in the luscious fruit-pieces of the late W. Hunt, where the bloom on the plum, the down of the peach, &c., are given with wondrous fidelity to nature. In the russet hues of autumn foliage, where purple and orange have broken or superseded the summer green, this interlacing of colour appears; and also in the olive foliage of the rose-tree, formed in the individual leaf by the ramification of purple in green. Besides the durable yellows, reds, and blues, the following orange and green pigments are eligible for mixed citrines. They may likewise, however, be safely and simply compounded by slight additions, to an original brown, of that primary or secondary tone which is requisite to give it the required hue.
| PERMANENT ORANGE. | PERMANENT GREEN. |
|---|---|
| Burnt Roman Ochre. | Oxide of Chromium, opaque. |
| Burnt Sienna. | Oxide of Chromium, transparent. |
| Cadmium Orange. | Veronese Green. |
| Mars Orange. | Viridian. |
| Neutral Orange. | Emerald Green. |
| Scheele's Green. | |
| Terre Verte. |
226. RAW UMBER,
or Umber, is a natural ochre, chiefly composed of oxide of manganese, oxide of iron, silica, and alumina. It is said to have been first brought from ancient Ombria, now Spoleto, in Italy. Found in England, and in most parts of the world, that which comes from Cyprus, under the name of Turkish or Levant umber, is the best. Of a quiet brown-citrine colour, semi-opaque, it dries rapidly, and injures no other good pigment with which it may be mixed. By time it grows darker, a disadvantage which may be obviated by compounding it with colours which pale on exposure. For light shadow tones and delicate grays it is extremely useful, and yields with blue most serviceable neutral greens. To mud walls, tints for stone, wood, gray rocks, baskets, yellow sails, and stormy seas, this citrine is suited. Some artists have painted on grounds primed with umber, but it has penetrated through the lighter parts of the work. Mérimée states that there are several of Poussin's pictures so painted; that fine series, "The Seven Sacraments," being clearly among the number.
227. Cassia Fistula
is a native vegetal pigment, though it is more commonly employed as a medicinal drug. It is brought from the East and West Indies in a sort of cane, in which it is naturally produced. As a pigment it is deep, transparent, of an imperfect citrine colour, inclining to dark green, and diffusible in water without grinding, like gamboge and sap green. Once sparingly used in water as a sort of substitute for bistre, it is not now to be met with on the palette.
228. Citrine Brown.
From boiling, hot, or cold solutions of bichromate of potash and hyposulphite of soda in excess, we have obtained an agreeable citrine-brown colour, varying in hue and tint according to the mode of preparation and proportions of materials employed. It is a hydrated oxide of chromium which, when washed and carefully dried, yields a soft floury powder. Transparent, and affording clear, delicate pale washes, the oxide has not been introduced as a pigment; partly owing to certain physical objections, and partly to a tendency to greenness. This tendency is peculiar to all the brown chrome oxides of whatever hue, whether hydrated or anhydrous; and indeed distinguishes more or less nearly all the compounds of chromium. Green, in fact, is the natural colour of such compounds, the colour which they are constantly struggling to attain; and hence it is that the green oxides of chromium, being clothed in their native hue, are of such strict stability. The inclination to green which the citrine under notice possesses, may be seen by washing the precipitate with boiling water. It has been supposed that hydrated brown oxide of chromium is not a distinct compound of chromium and oxygen, but a feeble union of the green oxide with chromic acid. If this be the case, the citrine cast of the brown oxide is easily explained, as well as the gradual addition to its green by the deoxidation of the chromic acid.
In mixed tints for autumn foliage and the like, the tendency to green of this citrine brown would be comparatively unimportant; but whether the oxide be adapted to the palette or not, we believe the colour might be utilized. In dyeing, for instance, the solutions of bichromate of potash and hyposulphite of soda would be worth a trial, the liquids of course being kept separate, and the brown washed with cold water. Various patterns could be printed with the bichromate on a ground previously treated with hyposulphite.