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.