Cobalt blue is an oxide of cobalt made by roasting cobalt ore. It makes a beautiful color, and works well in water or oil.
Smalt, Saxon blue and Royal blue are colored by oxides of cobalt.
There are a few other blues, such as Celestial or Brunswick blue, damp blue and verditer, that are chemical compounds, compounds of alum, copper, lime, and other substances; but they are so seldom used in this country that it is unnecessary to describe them in detail.
Yellows.—Chrome yellows are chromates of lead, produced by mixing dilute solutions of acetate or nitrate of lead and bichromate of potash. This makes a medium tint known as “middle chrome.” The addition of sulphate of lead makes this paler, when it is known as “lemon chrome,” whereas the addition of caustic lime makes it “orange chrome” of a darker color. The chromes mix well with oil and with white lead either in oil or water. They stand the sun well, but like other lead salts, become dark in bad air. Chrome yellow is frequently adulterated with gypsum.
Naples yellow is a salt of lead and antimony, supposed to have been originally made from a natural volcanic product at Naples. It is not so brilliant as chrome, but has the same characteristics. King’s yellow is made from arsenic, and is therefore a dangerous color to handle, or use for internal work. It is not durable, and it injures several other colors when mixed with them. Chinese yellow, arsenic yellow, and yellow orpiment are other names for this yellow.
Yellow ochre is a natural clay colored by oxide of iron, and found abundantly in many parts of the world. It is not very brilliant, but is well suited for distemper work, as it is not affected by light or air. It does not lose its color when mixed with lime washes as many other colors do. There are several varieties of ochres, all having the same characteristics differing only in color which varies from a golden to a dark brown.
Terra De Sienna, or raw Sienna, is a clay, stained with oxides of iron and manganese, and of a dull yellow color. It is durable both in oil and water, and is useful in all work, especially in graining.
Browns.—Browns generally owe their color to oxide of iron. Raw umber is a clay similar to ochre colored by oxide of iron. The best comes from Turkey; it is very durable both in water and in oil; does not injure other colors when mixed with them.
Burnt Umber is the last mentioned material burnt to give it a darker color. It is useful as a drier, and in mixing with white lead to make a stone color.
Vandyke Brown.—This color is an earthy dark brown mineral; it is durable both in oil and water, and is frequently employed in graining.