In fresco painting, the mason, or the plasterer, works with the painter. A surface as large as the artist expects to use during a few hours is covered with fresh stucco by the mason, and thoroughly smoothed with a small trowel. Stucco, as used in Italy, is a mixture of slaked lime and white marble dust, or very fine sand which has been thoroughly sifted. If stained to resemble coloured or veined marbles, and immediately ironed till it is dry with hot smooth irons, the surface of the mass is hardened and polished to such a degree that it is almost impossible to distinguish it from real marble without breaking into it. Waxing gives it a still higher polish. But if water-colours are used for painting a picture upon it, and if the colours are laid on while the stucco is still damp, they unite with the lime, and slowly dry to a surface which is durable, but neither so hard nor so polished as that produced when the stucco is ironed. The principal conditions are that the stucco must be moist, the wall behind it absolutely dry and the colours very thin and flowing. Should the artist not cover all that has been prepared for his day's work, the remainder has to be broken out again and laid on fresh the next day. It is now admitted that the wall-paintings of the ancients were executed in this way. As it was impossible for the artist at any time to have the whole surface of the freshly stuccoed wall at his disposal in order to draw his picture before painting it, he either drew the design in red upon the rough dry plaster, and then had the stucco laid over it in bits, or else he made a cartoon drawing of the work in its full size. The outlines were then generally pricked out with a stout pin, and the cartoon cut up into pieces of convenient dimensions, so that the painter could lay them against the fresh stucco and rub the design through, or pounce it, as we should say, with charcoal dust, like a stencil. He then coloured it as quickly as he could. If he made a mistake, or was not pleased with the effect, there was no remedy except the radical one of breaking off the stucco, laying it on fresh, and beginning over again. It was clearly impossible to paint over the same surface again and again as can be done in oil painting.