CHAPTER V. (XIX.)
Of Painting on the Wall, how it is done, and why it is called Working in Fresco.
§ 81. The Fresco process.
Of all the methods that painters employ, painting on the wall is the most masterly and beautiful, because it consists in doing in a single day that which, in the other methods, may be retouched day after day, over the work already done. Fresco was much used among the ancients,[[196]] and the older masters among the moderns have continued to employ it. It is worked on the plaster while it is fresh and must not be left till the day’s portion is finished. The reason is that if there be any delay in painting, the plaster forms a certain slight crust whether from heat or cold or currents of air or frost whereby the whole work is stained and grows mouldy. To prevent this the wall that is to be painted must be kept continually moist; and the colours employed thereon must all be of earths and not metallic and the white of calcined travertine.[[197]] There is needed also a hand that is dexterous, resolute and rapid, but most of all a sound and perfect judgement; because while the wall is wet the colours show up in one fashion, and afterwards when dry they are no longer the same. Therefore in these works done in fresco it is necessary that the judgement of the painter should play a more important part than his drawing, and that he should have for his guide the very greatest experience, it being supremely difficult to bring fresco work to perfection. Many of our artists excel in the other kinds of work, that is, in oil or in tempera, but in this do not succeed, fresco being truly the most manly, most certain, most resolute and durable of all the other methods, and as time goes on it continually acquires infinitely more beauty and harmony than do the others. Exposed to the air fresco throws off all impurities, water does not penetrate it, and it resists anything that would injure it. But beware of having to retouch it with colours that contain size prepared from parchment, or the yolk of egg, or gum or tragacanth, as many painters do, for besides preventing the wall from showing up the work in all clearness, the colours become clouded by that retouching and in a short time turn black. Therefore let those who desire to work on the wall work boldly in fresco and not retouch in the dry, because, besides being a very poor thing in itself, it renders the life of the pictures short, as has been said in another place.