One of the necessary qualifications of the painter is the knowledge of the colors that will stand the sun and weather. The manufactured chemical colors are generally not very durable, and are therefore not very suitable for outside work. The chrome yellows, chrome greens, and Prussian blues are fugitive, whether used alone or mixed. A combination of two colors of durable nature is often subject to change of tone. Of the more durable colors for external use, the ochres, Indian and Venetian reds, burnt and raw umbers, and burnt and raw siennas may be mentioned. Zinc white, though of less body than white lead, is more delicate and durable, and should always be used in place of white lead at the seashore, where it is especially durable. The action of the salt air injures the lead. The most durable blacks are lamp-black and vegetable black, the most durable yellows are yellow ochre and Naples yellow, both of which have a good body. Chrome yellow is fugitive, and, like other lead salts, it becomes dark in bad air. Of the reds, those to be depended on are the Venetian red. Indian red, light red, and madder lake; carmine lake vermilion, and chrome red are best avoided on the exterior. The only blue that will stand is ultramarine, though it is expensive. Prussian blue, cobalt.

Antwerp blue, and indigo will fade either singly or in combination. The umbels and siennas, burnt and raw, burnt ochres and Vandyke brown, are permanent colors. Raw umber is very durable in both water and oil, and does not injure other pigments when mixed with them. The same may be said of yellow ochre, a natural-colored clay, which does not lose its color when mixed with lime, and hence it is well adapted for distemper painting. Mixed greens are not so durable as those direct from copper, arsenic, etc., which are, however, injurious to health. Emerald green made of verdigris and a solution of arsenious acid, and Scheele's green and Vienna green, arsenites of copper, are very poisonous.