4. Design refers to the expression of a proposed picture in simple contour, or outlines. It is applied in making the first rough sketch of the picture, whether in miniature or in its full size, as well as in the more accurate expression of the form of the figures, in its final finish. The artist, in making his design, is guided in drawing his lines by the rules of perspective, according to which he is able to foreshorten objects, and thereby diminish the space which they occupy, without giving them the appearance of diminished magnitude.
5. Perspective has been defined the art of delineating the outlines of objects on any given surface, as they would appear to the eye, if that surface were transparent, and the objects themselves were seen through it, from a fixed position. For example; when we look through a window at a mass of buildings, and observe that part of the glass to which each object, line, or point appears opposite, we find that their apparent position is very different from their real. A delineation of these objects on the glass, as they appear, would be termed a representation in perspective.
6. Correct perspective is the foundation of scientific painting; and, next in importance to this, is a proper distribution of light and shade. This branch of the art is called chiaro obscuro, or, when abridged, chiaro-scuro. The term is Italian in its origin, and its literal meaning is clear and obscure. To the skilful management of light and shade, we are indebted for the strength and liveliness of pictures, and their relief, or the elevation which certain parts appear to assume above the plane upon which the objects are represented.
7. By the aid of perspective and chiaro-scuro, very good representations in one color are attained. Drawings in India-ink and crayons, as well as pictures taken from engraved plates and wood-cuts, are specimens of such productions. But a nearer approach to the appearance of nature, is made by the employment of colors analogous to those which are found to exist in the objects to be represented.
8. To produce various hues in painting, the artist employs coloring substances, which, either alone or by mixture, are analogous to them all; and, in their use, he is careful to apply them in such a manner, that the true colors remain distinct from the lights and shades necessary to produce the objects in relief. Artificial colors are divided into warm and cold. The former are those in which red and yellow predominate; the latter are blue, gray, and others allied to them.
9. Before coloring substances can be applied in painting, they must be reduced to extreme fineness, and be mixed with some tenacious fluid, to cause them to adhere to the surface on which they are to be spread. The fluid employed for this purpose, and the mode of applying the colors, have given rise to the different kinds of painting, of which the following are the principal: crayon, water-color, distemper, fresco, and oil-painting.
10. The most simple mode of applying the colors is by means of crayons. They are made of black lead, a species of chalk, or of a mixture of coloring matter with gum, size, or clay. For painting in water-colors, the substances employed in communicating the tints are combined with gum, and formed into cakes or lozenges. When about to be used, they are dissolved in water, on glass or a glazed surface. The application in painting, is made by means of a camel's-hair pencil.
11. Painting in distemper is used for the execution of works on a large scale, such as stage scenery, and the walls of apartments. The coloring substances are mixed with water, rendered tenacious by size or solutions of glue, or by skimmed milk, increased in tenacity by a small quantity of thyme. Linseed or poppy oil often serves as a vehicle for the colors, in this kind of painting.
12. Paintings in fresco are executed on walls of plaster. The coloring matter mixed with water, being applied to the plaster while the latter is in a fresh state, sinks in, and incorporates itself with it, so as to become very durable. During the execution of the work, the plaster is applied to the wall in successive portions, no more being added at a time, than can be conveniently painted before it becomes dry. Works of this kind must be executed with great rapidity; and, on this account, patterns, called cartoons, are previously drawn on large paper, to guide the artist in his operations.
13. Oil painting derives its name from the mixture of the colors in oil. The oils used for this purpose are extracted from vegetables; and, on account of the rapidity with which they dry, are denominated drying oils. For most purposes, this mode of painting is decidedly superior to all others. It admits of a higher finish, as it allows the artist to retouch his works with greater precision. The colors also blend together more agreeably, and produce a more delicate effect. Oil paintings are executed on canvas, wood, or copper.