VANDYKE BROWN.--What the original brown used so much by the great Van Dyke was no one can tell. The pigments now sold under the name of Vandyke brown are of varying composition, some being simply mixtures of red oxide of iron and lamp black, others are natural earthy substances after the character of Cologne earth, and others again are artificial products of the partial carbonisation of vegetable matters, such as cork waste. As it is uncertain what was the composition of the original Vandyke brown, no standard of chemical purity can be established. Probably the most general sources of Vandyke brown are red oxide and lamp black, and the quality of such a pigment will chiefly depend on securing a good black, as any traces of unburned oily matter will make the paint difficult to dry. Almost any variety of shade can be produced by adjusting the proportions of lamp black and red oxide, with sometimes the addition of a little ochre. The pigment made in this manner forms the staple brown paint for industrial application, mixing well with oil, and being of a durable character, but it does not mix so well with water. Vandyke browns of the Cologne earth type, from earthy lignites and peaty matter, are much used in and around the localities where they are produced, and entail nothing more than grinding and levigation to fit them for the market. They are in general best adapted to water-colour painting. Warm and slightly reddish tints of Vandyke brown are obtained by the partial carbonisation of ligneous material, in other words by subjecting cork and bark waste to moderate calcination in closed retorts. These mix equally well in water or oil. All varieties of Vandyke brown are stable pigments, without any disturbing influence when used in admixture with other colours, and quite proof against any change on exposure to air and light. Next to the umbers they are the most generally useful browns. CHAPTER V. GREENS. Green pigments form an important and numerous class, but many of those which possess the most brilliant and durable qualities contain highly poisonous ingredients, and some of the most beautiful are not permanent. All things considered they are perhaps the least satisfactory group of colouring matters. The following list comprises all worth notice.