Owing to the totally absorbent quality of canvas, and the more or less partial transparency of oil colours, it is necessary for finished work to prepare the canvas with some coating, in order to prevent the painting sinking into the canvas; this coating is technically called a ground. Before choosing a ground for your work, it is important to understand what are the qualities most essential for a good ground on which to paint. This may, to a great extent, be learnt from the experience of others. The next thing is to find out what sort of texture is most suitable for your own work, and how to get this texture; and this you can only learn from personal experience and carefully-made experiments. There is no doubt that its being partially absorbent is the first essential for a good ground. If this quality is secured, the oil with which the colours are mixed can penetrate through the ground to the canvas, and oil being a strong cement, it binds all the particles firmly together. With the ordinary fully-primed, smoothly prepared canvas, the oil not only cannot penetrate, but there is no grain or tooth to hold the colour. After a few years the painting cracks and [86] shrinks from the polished surface with which it has never really united, in some cases slipping down in large pieces from its original place. The rapid and utter ruin of many masterpieces, both by Sir Joshua Reynolds and Turner, may, to a great extent, be attributed to their careless use of these "prepared" and non-absorbent canvases. The first house-painter they met could have taught them better. House-painters know well from experience that to make a fresh coat of paint last, the old paint must be sufficiently removed to allow the oil of the new painting to penetrate the wood, and that a necessary amount of texture must be gained by the use of pumice-stone and sand-paper. For rapid sketches nothing can be better than smooth absorbent wood, such as the panels you buy for the French sketching-boxes. This wood being smooth and sufficiently absorbent, the oil dries or rather sinks in directly, thus allowing you to complete your work at once. If you use canvas, choose half-primed canvas. This being prepared with size and whitening only is, to a certain extent, absorbent. Choose a fine but rough texture, so that in passing your finger over it you feel the tooth. This grain gives a hold to the colour. If you get an ordinary fully-prepared smooth canvas or the usual oil-paper, your colours run [87] into one another, rendering it impossible without the greatest care to get much finish in your work at one painting. Even if you do succeed in getting the impression you wish at one painting, on putting your sketch when dry out in the sun you will find the colour peel and crack off. This result is a sure sign that such work will not last. As I have already stated, for pictures and finished work it is necessary for the artist himself to prepare his canvas. There are two methods of preparing grounds -one tempera, the other oil. The following are simple instructions for either process. Artists have many slightly differing methods for preparing their grounds, methods which some are inclined to cherish as important secrets; but the principle of all is identical, and the differences very slight.,,