Having chosen with the greatest care the materials required for painting, we have still to know on what we are going to paint; the question of canvas, panels, etc,. is one of great importance. A picture is composed of three altogether distinct elements:-,1.The support, or the material substance painted on, as wood, canvas, stone, paper, etc.,2.The coating or sizing used to cover the material support.,3.The final painting, formed by successive layers of colour applied over the sizing.,If the painting be done under bad conditions, and contain in itself the germs of its destruction, spoken of above, the picture is irretrievably lost, and that in spite of the good quality of the support, and of the sizing. But admitting the hypothesis that the painting is as perfect as it ought to be, it is also necessary that the two other constituent parts of the picture (i.e. the support and the sizing) should be perfect. The support will first be chosen as substantial as possible, but it can still be preserved from many causes of destruction by covering it behind and on the sides by means of mastic and suitable protective varnish. (see Appendix-"Panels of unpolished wood). If, however, it happens to spoil even when all precaution has been used, a clever picture restorer can still save the painting by transfering it to another canvas or panel, always provided that the sizing sustaining it remains in good condition. [continues to describe the condition of "triqueterous alter screens" where the centre panel is in poor condition due to its attachment to a damp wall, and the side panels remain in good condition. In those conditions, when the sizings are good, the painting is equally preserved on the middle panel and on the side leaves, whilst on the contrary on bad sizings, the painting is spoilt on the rotten panel and preserved on the leaves in good condition. In fact, therefore, the preservation of the painting depends on the quality of the sizing. It is not enough that the sizing should be solid: were it like steel, indestructable as the diamond, we should still require to have it less brittle; for should it scale off, melt, or powder, it would involve the painting with it. It must even be sufficiently supple to lend itself to the peculiarities of the painting, as it contracts when drying, and yet it must be of sufficient resistance to preserve the painting from too sudden movements of the support. It should absorb the excess of oil and varnish which comes to it from the painting, and it should reject all which might penetrate through the support. In short, compelled to obey the slightest caprices of the one and to resist all the attacks of the other, it is required from it, as from all servants, to be equal to the occasion. Notwithstanding the importance of the role which the sizing plays, and perhaps rather on account of this importance, it is often suppressed -first, for painting on paper in water-colours and pastel where it is not necessary, and sometimes even for oil painting when done directly on the support. In this case supports should be chosen having something of the qualities the sizing would have had -i.e., dilating little and shrinking little, of a fine texture, uniformly porous, and containing neither acids, resin, nor any other matter capable of influencing the colour; if found too absorbent it will be well before painting to brush the support over with a little re-touching varnish, or painting varnish, or a mixture of both, according to whether the painting is to be in a dry style, or the colour is to glide smoothly over the surface., ,,