Canvas is now what may be called the universal subjectile for pictures in oil. There is a fashion in these things, as in others, and you will hear an ignorant person invariably express contempt for a modern picture done on wood; so that, even for the size we have mentioned just above [cabinet size,see under panels], cloth has greatly the preference; with what reason, it is not for us, in 'this' volume to consider. Canvas is sold at so much the square foot; that which is twilled, or ticking as it is otherwise called, costing fifty per-cent more than the plain. It is kept, ready-primed, in rolls of various width, at the colormen's, who need but a few hours notice to cut it and distend it on the frame to any proportion that may be desired. There are however certain sizes which have obtained for many years among artists, especially for portrait-painting, and these are always kept on hand at the shops, ready-mounted on the frames, or stretchers. Certain names are sometimes given to indicate certain of these sizes, and as the student may sometimes meet with them in books, or hear them mentioned, it is right he should know them. The Kit-kat (the original of which cant name may be found in a note to one of Taylor's books) is 28 or 29 by 36 inches; Three-quarters, -25 by 30; Half-length, -40 by 50; Bishops' Half-length, -44 or 45 by 56; Bishops' Whole-length, -58 by 94. ,The use of a simple frame, without the means of distending the canvas that is nailed to it, when it shall have become lax, is enitrely out of date: what the French call Châssis à clefs, i.e., frames with keys, are now unversally adopted for the smallest as for the largest canvas. These frames consist of four uniform pieces of deal, whose width and thickness vary according to the size of the cloth, put together with tenons and mortices precisely as the frame of a schoolboy's slate, only that they are not fastened by pegs or otherwise; the canvas alone, which is tacked to the frame, keeping them together. Two wooden wedges (the keys above mentioned) are inserted into each corner, so as to be between the tenon and mortice of each side; and by gentle blows with a hammer on these wedges the parts of the frame divaricate, and the cloth in consequence stretches. In striking these wedges, you will observe to go all around the frame, blow for blow, or rather tap for tap (for it must be done lightly), giving to each wedge one stroke in succession, till your canvas is sufficiently distended. If you were to drive home, or finish hammering, the wedges of one side, before touching the others, you would spoil the square of your picturecloth; and this irregularity you would often, in the course of your sketch, find embarrassing.,It is advisable to purchase your canvas many months before using it; a year indeed is none too long. Keeping it then where it will be exposed to the air, and the light, and even to the sun if not too warm, the priming of the cloth has a chance to become 'perfectly' dry, and thus the 'oil', wherewith it was prepared, is less likely to add its pernicious effects to those of the oil which you yourself are obliged to use. Before using it, rub it over with pumicestone (putting your left hand behind the cloth, so as to prevent injuring it), and wash it off with water, to which may be added a portion of alcohol. The fineness of the cloth should be proportioned to the size and subject of the picture. You cannot have too smooth a surface for a small cabinet picture which will be examined close at hand; whereas in one of the large dimensions this is less necessary, and a canvas somewhat coarser is even preferable because it holds the paint better. The great essential is that the cloth be as free as possible from knots. If these be covered, make no objection to the thinness of the priming. ,As to the tint given to this preparation, it is better that it should be light. Of the three kinds which are usually found in the shops, light gray, pink, and the faintest flesh-color, this last is the best. A color like that of old ivory is perhaps as good a tint as one could have for the priming of a canvas whereon a head or heads are to be painted.,Ticking or twilled canvas is also used for picturecloths, as we have intimated; but more rarely. From its peculiar fabric, it has some advantages, and where a double cloth is desired, it would be excellent for the under one or lining, on account of its strength. ,A double canvas promises of course much greater durability, in itself, and greater protection for the colors against the atmosphere. The mode of preparing it is the same as what is called the lining of a picture, of which, in its proper place, we shall have to speak, for the benefit of the amateur. (see Part VII., Chapter iv.) ,Perhaps the chief reason, certainly one of the most important reasons, for the preference given to canvas over the old wood panel, has been the ease with which a picture may be transported from place to place. If the reader will recollect the size of Mr. Wier's great picture of the Embarkation lately exhibited in this city, he will see that it could not have been admitted through the doors of the exhibition room, except by taking it off the frame. In doing this, and rolling up a picture, the painted side is to be kept outward, because in the case of paint craking, it will join again when the canvas is spread; whereas, the contrary way, the paint is crowded and crushed together, and, if it does not scale off, it will open in cracks as soon as stretched. The same precaution is of course necessary in the rolling up of a canvas that is merely primed.