In nearly all the methods of painting known to the ancients, water was employed as the vehicle, either alone or mixed with some glutinous substance serving to bind the colors together. Paintings in distemper, frescoes, and miniatures are all varieties of water-color paintings; but the term is now applied almost exclusively to painting on paper with colors diluted with water. The best Italian, Dutch, and Flemish painters often executed their cartoons and finished sketches with water colors; but these were mere studies, and pictures in water colors on paper, intended for exhibition as completed works of art, are much more modern. They were at first executed exclusively with solid opaque colors, and the use of transparent colors first became general toward the end of the last century. The name of "stained drawings" was at first given to paintings in this latter style; and the drawing was in general made out in light and shadow with India ink or some neutral tint, and washes of transparent colors were then applied to the different parts.

The plan now generally pursued is to paint in every object at once in its proper colors, without the use of a preparatory monotinted ground, trusting to subsequent modifications, commonly made with transparent, though sometimes with opaque colors, to remove the first crude effects. The superior facility of painting in this manner, as well as of rapidly sketching evanescent atmospheric appearances, has greatly tended to popularize the art. The number of water-color painters is now very large, especially in England, the United States, and France; and in Great Britain there are special societies of painters in water colors. - The practical details of the art vary so much with different artists, that scarcely any general rules can be laid down. Some prefer a paper with a fine grain, and others with an exceedingly rough one. The paper most generally used is that known as imperial, which comprises a great variety of textures and thicknesses. Graduated tinted papers are also employed, having preparatory hues for different hours of the day or for the production of other effects. If the surface of the paper is at all greasy, so that the colors do not adhere well, it should be sponged over, or the colors may be mixed with water to which a little ox gall has been added.

A peculiar texture is sometimes imparted to parts of the paper by rubbing, sponging, etc, and some of the finest landscape effects are thus produced. The colors employed, except gamboge and sap colors, do not differ from those used in oil painting (see Paints), and are either made into hard cakes with gum, or used "moist," or prepared with honey or some saccharine material. Moist colors are generally also made into cakes, though they are sometimes brought to a semi-fluid consistence and enclosed in thin leaden tubes, from which they may be squeezed out in small quantities as needed. Colors so prepared are chiefly used for large works or when a considerable body of color must be laid on in a short time. The mixing of Chinese white with the pigments so as to render them opaque (a practice strongly advocated by Ruskin) constitutes body-color painting, as opposed to transparent-color painting. The principal colors are ultramarine, indigo, Antwerp and cobalt blues, gamboge, ochre, Indian and chrome yellows, Indian red, vermilion, lake, carmine, burnt ochre, and brown pink reds. Out of these primary colors all the others may be compounded; but sap green and several browns, as raw and burnt sienna, Vandyke brown, umber, sepia, etc, may also be used.

They are generally mixed with water alone, but gum and other substances are sometimes added to give depth to the shadows and brilliancy to the lights. Brown sable brushes are generally used.