A vehicle is any liquid which is mixed with the color to make it fluent. The vehicle may be ground with the pigment or mixed with it on the palette, or both. Oil colors are of course ground in oil as a vehicle; but it is often necessary or convenient to add to them, in working, such a vehicle as will thin them, or make them dry better. Those which thin or render more fluent the paint are oils and spirits; those which make them dry more quickly are "dryers" or "siccatives."

All vehicles must of necessity have an effect on the permanency of the pigments. Bad vehicles tend to deteriorate them; good ones preserve them.

Oils.—The most commonly used oils are linseed and poppy oil. They are neither of them quick dryers, and are usually mixed with sugar of lead, manganese, etc., to hasten the drying. These have a tendency to affect the colors; but if one will have recourse to none but the pure oils, he must be patient with the drying of his picture. For this reason it would be well to use vehicles with the colors on the palette as little as possible—and that is against thin and smooth painting.

Oil has the tendency to turn dark with time, thus turning the color dark also. The only way to reduce this tendency is to clarify the oil by long exposure to the sunlight. The early German painters used oil so clarified, and their pictures are the best preserved as to color of any that we have. But the drying is even slower with purified oil than with the ordinary oil.

It would be best, then, to use oil as little as may be in painting, and if you need a dryer, use it only as you actually need it in bad drying colors, and then very little of it.

The essences of turpentine and of petroleum may be used to thin the paint, and are preferable to oil, because they have less darkening tendency. They do not, however, bind the color so well, and the paint should not be put on too thinly with them. Usually there is enough oil ground with the pigment as it comes in the tubes to overcome any probability of the paint scaling or rubbing when thinned with turpentine, but in the slow-drying, transparent colors there will be a liability to crack. Moderation in the use of any and all vehicles is the best means of avoiding difficulty. Use vehicles only when you need them, not habitually, and then only as much as there is real need of. If you use oil, use the lighter oils, and expect some darkening in time. Prefer turpentine to oil, and expect your color to dry rather "dead," or without gloss, by its use. If you intend to varnish, this is all right. If you do not intend to varnish the picture, keep the color as near the pure tones as you can. The grayer the color, the more the "dead" or "flat" drying will make it look colorless.

Varnishes.—When the picture is done, after it is dry, varnishes are used to bring out the freshness of color, and to preserve the surface from outside influences of all sorts. A picture must be well dried before it is varnished, or it is likely to crack; six months is not too long to be safe. If you are in a hurry to varnish, use a temporary or retouching varnish.

The best varnish is necessary for use on pictures. Never use any except a varnish especially made for the purpose by a reliable colorman. Those made by Winsor and Newton may all be depended upon. Pay a good price for it, and don't use too much.

Mastic varnish is that which is most favorably known. Be sure you get a good and pure quality.

Varnishes are made from various gums or resins dissolved in a solvent such as alcohol, turpentine, or oil, as the case may be. The lighter gums are the best for pictures, because they do not affect the color of the picture. Much care should be used in putting on the varnish—that it is even and as thinly distributed as will serve the purpose. It should not be flowed on, but carefully worked out with a clean brush, and then kept from dirt and dust until dry.

The finer varnishes in oil or turpentine are best for ordinary use. Those in alcohol do not hold their freshness so well.

Varnishes are sometimes used as siccatives, and to mix with colors which are liable to affect other colors, or to lack consistency. Usually, however, they are not needed.