ORANGE, VIOLET, and BROWN are the remaining color groups combined from the primaries. These, unlike original green pigments, are easily mixed and thus are not needed in the palette as independent colors. This is particularly true of orange and violet. There is, however, an orange in the cadmium range. Pure violet, as made by mixing alizarin red and ultramarine blue, does not exist as a pigment. Ultramarine and cobalt violets should be mentioned for work on lime grounds; the latter, cobaltous oxide arsenate, is one of the few really poisonous substances in the palette. Their intensity or tinting strength is not very high.
There are, on the other hand, several valuable original browns derived from natural earth colors which can be made darker and redder and at the same time more dense by burning.
BURNT SIENNA is the most important brown pigment. The purest form of iron oxide is the coloring agent; its reddish
color is very difficult to copy in a mixture.
Raw Sienna, the hydrous iron oxide of Sienna earth in its natural state, is much less important as a color. Although it has covering power, it remains a transparent color which is unpleasantly obtrusive when laid thick and is hardly ever to be used unmixed. Over underpainting in other colors, however, it is a brilliant and light glaze. Direct mixtures are possible with most pigments for subtle, dull nuances.
UMBER is the darkest original brown pigment. The best natural kind, Cyprian umber, acquires a very dark, reddish tone when burnt. The active agent in this is the iron particles in the earth, which
owes its characteristic color mainly to compounds of manganese.
Umber, both burnt and raw, is the classical shadow color. Burnt umber certainly has a shady character in some respects! It is heavy in tone and opaque, and in spite of its high tinting strength it tends to make "holes" in the picture and, like almost all dark pigments, it delays the drying time of oil binders. Nevertheless burnt umber is vuluable for darkening all colors, much better in effect than black, and it makes a good rich black when mixed with Prussian blue. Without umber Rembrandt would ha;dly have succeed.ed in painting his mysterious shadows.
CAPUT MORTUUM derives its strange name from the color of the skulls in the
Roman catacombs, though in fact it -has little in common with them coloristically,
and nothing at all as material. It is a synthetic compound of manganese which can be produced in a great variety of nuances, based on two varieties, one a deep red-brown and one violet-brown. Being already very unclear colors and lacking in intensity, they are not good mixers. The violet variety gives the shadow tone of newly ploughed earth or, when used as a half-glaze, the color of young swelling buds in springtime, that mauve haze that seems to hover in birch trees or shrubs before the buds have burst. It is a useful addition to a modest palette.
All brown pigments are easy to handle technically. Even the slow drying effect of burnt umber can be helped by a small addition of cobalt or lead pigments.
Brown pigments show most clearly the convenience of having a series of consistent, mixed tones on the palette. Although it is easy to mix these unclear colors from strong brilliant ones, it saves a great deal of time to have the original pigments for them, and it helps the visualization of color effects to have the mixed tones ready at hand. Thus, it is rational neither from the point of view of time, nor of technique - nor financially - to have too few basic colors. It is best to make use of all the available pigments which are valuable for color and are technically uncomplicated; they are not so very numerous.
You should be warned against fancy trade names, however, and, once again, be advised ag,ainst the ready-mixed paints offered for sale.