Many of the pigments which change color by the action of impure air, and are, therefore, useless in water-color painting, may, nevertheless, be safely used in oil painting; for this reason: In water color the powder colors are mixed with only just enough of some binding cement (called a vehicle), such as gum, size, sugar, etc., to prevent their being easily rubbed off the paper, and are, therefore, freely exposed to the action of the atmosphere, or of the colors with which they may be mixed; but in oil colors the powder colors are ground up in oil, so prepared as to oxidise rapidly in the air into a kind of impermeable leathery resin, which, completely enveloping each particle of color, effectually protects it, not only from the action of impure air, but also of neighboring particles of different colors. And it thus happens that pigments may be used in oils with tolerable safety which in water color might turn black in a few days. Indeed, the white which we invariably use in oils - flake white - is certainly one of the most unstable of colors in water colors; and nearly the same may be said of the chrome yellow, Naples yellow, emerald green, etc. The colors named below will be found a useful set:

Flake White, Ultramarine, Prussian Blue, Yellow Ochre, Carmine (in Powder)* Indian Red,

Lamp Black* Cappagh Brown, Raw Sienna, Cadmium Yellow* Rose Madder* Emerald Green*

Cobalt Blue, Madder Brown* Burnt Sienna, Pale Cadmium Yellow* Indian Yellow*

The colors marked with an asterisk do not dry quickly, except when mixed with much flake-white. To these it is necessary to add a very little drier - a mixture of sugar of lead and boiled oil.

Brushes. - After the colors, the brushes are the most important part of the artist's materials. Flat hog's-hair brushes are the most useful for general purposes. These should have polished handles, and the hairs should not straggle at the point, but keep together, so as to form a straight, thin edge. The small sizes are most convenient when made very short and very thin in the hair, it being difficult to make the long-haired ones keep together at the point. For fine touches, sable brushes are the most convenient, some flat and some round; the former thin and short-haired, the latter coming to a fine point.

Badger's-hair softeners are used, as their name implies, to soften broad tints in skies, etc., but require the greatest caution in their use, or they will certainly produce a disagreeable "wool-liness," or smudginess. They are made with the hair radiating, or spreading out, towards the point, and are used by dabbing or jobbing them lightly over the work, and should always be used clean and dry.

The brushes should always be cleaned as soon as they are done with for the day. The easiest way is to rinse them in a little spirits of turpentine, and, after drying them on a rag, wash them out clean by rubbing them in the palm of the hand with thick soap and water, and then rinsing them in clean water, and allowing them to dry with the hair in its proper position. It happens sometimes that, leaving off in a hurry, one has no time to wash out the brushes carefully. In that case they may be laid by for a few days, dirty as they are, with their ends under water. The paint will keep under water without drying.

Canvas. - This is the best material for painting upon. It is sold ready stretched on frames, and is kept of all sizes at the artists' color warehouses.

Prepared Paper is perhaps the most convenient material for the beginner, occupying so very little space when the picture is dry. It must be fastened, when in use, to a board by means of drawing-pins. It is also kept bound up into blocks, like those used for water-color sketching, and this is, perhaps, the most convenient form in which to buy it, though not the cheapest.

Millboards seem to me to possess no advantage over paper, and are very heavy, and liable to break at the corners.

Panels are heavy and rather bulky, but are peculiarly well adapted for works requiring high finish.

Palettes are usually made of mahogany or satin wood. The latter are the best, the colors being better seen on the lighter colored wood. The rectangular shape is the most convenient, and packs best into the lid of a color-box. A wooden palette should have plenty of raw linseed oil rubbed into it before being used, and be allowed to dry. This will prevent the colors sinking into the wood and staining.

A Dipper is a small tin cup made to fix by sliding on to the palette, to contain oil, turpentine, varnish, or any other vehicle used.

The Rest Stick is used to rest the right hand upon, while painting those parts of the picture that require great steadiness and care. It should be as stiff and as light as possible, and is held in the same hand as the palette.

Palette-knives are necessary implements for mixing and manipulating the colors on the palette. It is convenient to have two of different stiffness.

Easels are inconvenient usually in proportion to their cheapness. They should be tolerably firm and heavy, and should allow the picture to be raised easily and quickly.

Vehicle is the diluent used to temper and thin the colors for the purpose of bringing them to a proper state. Linseed oil, rendered drying by boiling with certain metallic oxides, is the vehicle generally used. Drying oil should dry quite free from stickiness in two or three days, in ordinary weather. Copal varnish is also an excellent vehicle, but dries so rapidly that it will not do where the colors require considerable manipulation with the brush - as in skies and broad tints generally. Colors used with varnish will require frequent thinning with spirit of turpen-tine. Megilp is a most pleasant vehicle to use; so pleasant, indeed, that one is apt to use far too much of it. It is made by mixing strong mastic varnish with drying oil.

The beginner should bear in mind that all oils and varnishes have a strong tendency to turn dark brown with age, and should therefore learn to use as little as possible; indeed, the colors, as generally sold, are ground with sufficient oil for use with a hog's-hair brush; and it is only where greater freedom is required, and when using sable brushes, that an addition of vehicle is of use. It is absolutely necessary, however, in the process called "glazing," which is where a transparent color is rubbed thinly over parts of the picture, the general tone or color of which it is desirable to modify. And in this case, too, as little vehicle as possible should be employed.