Much diversity of opinion has existed respecting the colour of the surface of the prepared canvas. It is a subject of considerable importance, for it is impossible to paint a richly-coloured picture, with life and warmth, upon a dull unsuitable ground. A landscape, if carefully handled, can be brought on and finished in a more brilliant manner on a white ground than on any other. It has however been objected to a purely white ground, that it is liable to impart a cold chalky effect; but it must be . remembered that what is at first white in oil, becomes in a short time of a yellowish hue, and its coldness of tone is thereby lowered. The white, or pale cream-coloured, and pale warm drab-coloured grounds, seem to surpass all others. The reason is that they throw a light, and consequently a transparency, through the work; and, as all colours in oil painting have a tendency to sink into the ground on which they are laid, and to become darker, this tendency can be counteracted only by having grounds of considerable lightness and brilliancy.

Cold grey grounds have been used in landscape painting; but they impart a heaviness of colouring much to be avoided. Some artists have painted on grounds of a dull red or leather-coloured tint, and much richness may be gained by such; but after a time the colours of any portion that may have been thinly painted sink into this strong ground, and the effect produced is heavy and disagreeable. Upon the whole, a white ground is to be preferred, as soon as the learner has acquired some experience of the subsequent effect of his colours; but as the inexperienced find much difficulty in preventing the coldness and poverty of expression which it is likely to cause under their hands, it will be advisable for the beginner to take the usual light stone drab that is generally given to canvas; for it furnishes him with a middle tint or tone to start from, which, when visible in shadows and middle tints, has not the raw chalki-ness shown under similar circumstances on an unskilfully or imperfectly covered white ground.

Vehicles are used to temper and thin the colours, for the purpose of bringing them to a proper working state. All oils or varnishes act more or less to the eventual prejudice of the colour with which they are combined for application. What is desired in oil painting is a vehicle which, while it has an agreeable working quality, shall neither change nor be degraded by time, nor interfere with the. purity of the tints as they appear at the moment they are first laid on - a vehicle, that shall neither perish nor crack as it becomes old.