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 an 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Naples yellow is a salt of lead and antimony, supposed to have been originally made from a natural volcanic product at Naples.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.
Fig. 19. Round Badger Blender.
All the hues and tints, from the palest lemon cadmium to the orange red, are due to one compound only of cadmium, namely the sulphide, which contains 112 parts by weight of cadmium to 32 parts of sulphur. As commonly prepared cadmium yellow is of an orange hue; when this compound separates slowly from a solution, or is made in any way to take a dense or aggregated form, it becomes of a decided reddish orange. The orange-yellow variety, when very finely ground, becomes less red and more inclined to yellow. Some of the palest cadmium yellows contain white pigments or flour of sulphur, added to reduce their depth of color. Yellow cadmium is prepared in several ways. A slightly acid solution of any cadmium salt is prepared and through it is passed a current of sulphuretted hydrogen gas. The product thus obtained has a pure chrome yellow shade. A lemon yellow shade may be obtained by dissolving 1 pound of cadmium sulphate in 4 gallons of water and adding 1 1/4 gallons of the ordinary yellow ammonium sulphide.
Cobalt yellow is a compound of the nitrates of cobalt and potassium. It is prepared by precipitating cobalt nitrate with sodium carbonate, dissolving the precipitate in acetic acid and adding a strong solution of potassium nitrate. On allowing the mixture to stand for some time the color is gradually precipitated, and is collected, washed and dried, when it is ready for use.
Cobalt yellow is a pure yellow color, and is almost transparent whether used in water or oil painting.
Orange ochre also called Spanish ochre is a very bright yellow ochre, burnt, by which operation it acquires warmth, color, transparency and depth.
Mars orange is an artificial ochre similar to the above. It is made by taking equal weights of ferrous sulphate and alum, and adding a solution of carbonate of soda, thereby precipitating the iron and alumina. The precipitate, which forms a yellow pigment, the so-called Mars yellow, is collected, washed well with water, dried and converted into orange, by slightly calcining.
Oxford ochre is a native of the neighborhood of Oxford, England; it is semi-opaque, of a warm yellow color, and of a soft argillaceous texture, absorbent of water and oil, in both of which it may be used with safety, according to the general character of yellow ochres, of which it is one of the best.
Stone ochre has been confounded with the preceding, which it frequently resembles, as does also Roman ochre. True stone ochres are found in balls or globular masses of various sizes in the solid body of stones lying near the surface of rocks among the quarries in Gloucestershire, England, and elsewhere. These balls are of a smooth compact texture, in general free from grit, and of a powdery fracture; they vary exceedingly in color, from yellow to brown murrey and gray, but do not differ in other respects from the preceding, and may be safely used in oil or water in the several modes of painting. Varieties of ochreous colors are produced by burning and compounding with lighter, brighter and darker colors, but often very injuriously and adversely to a certainty of operation, effect and durability.
Raw sienna is a ferruginous, or impregnated with iron, native pigment, and appears to be an iron ore which may be considered as a crude, natural yellow lake, firm in substance, of a glossy fracture, and very absorbent. It is in many respects a valuable pigment, of rather an impure yellow color, but has more body and transparency than the ochres, and being little liable to change by the action of either light, time, or impure air, it may be safely used, according to its powers, either in oil or water, and in all the modes of practice. By burning, it becomes more transparent and drying, and changes color to a red brown. Raw sienna is a valuable color in graining.
There are several pigments called yellow lake, varying in color and appearance according to the coloring substances used, and modes of preparation; they are usually in the form of drops, and their colors are in general of a bright yellow, very transparent, and not liable to change in an impure atmosphere, qualities which would render them very valuable pigments were they not soon discolored and even destroyed by the opposite influences of oxygen and light, both in water and oil, in which latter vehicle, like other lakes in general, they are bad dryers, and do not stand the action of white lead or metallic colors. If used, therefore, it should be as simple as possible.