Fresco - Painting Procedure

The main points in the painting procedure can be summarized as follows:

1. The section of plaster intonaco must be given a little time to set [about twenty minutes to one half hour] before it can be painted upon.

2. The cartoon drawing is transferred to the intonaco by pouncing, or incising.

3. The first washes of color, ground only in distilled water, can be set in, as in watercolor. They can be thinned with water to the lightest wash, letting the white intonaco show through to make the color luminous and transparent.

4. If several thin washes of the same color are laid one over the other, the color effect becomes darker, more opaque, and intense. The moisture of the color wash must be allowed to sink into the plaster before the area is repainted.

5. Painters who wish to obtain light colors through mixtures with opaque white, rather than through transparent washes, can mix the colors with lime putty or bianco sangiovanni. Both of these whites tend to be transparent when wet and become intensely white when they dry. Thus as in gouache and distemper painting, artists must allow for a lightening of tone when they mix their colors with these whites. Some painters make up such mixtures in advance and test each of them on an absorbent scrap of white wood or on a test brick painted with lime putty to see what color it will have when dry. Then they keep in a jar enough of the color mixture to cover the area for which it is intended. Other painters simply mix the colors on the palette as they progress, much in the same way as they do in gouache or distemper. Titanium dioxide mixed with lime putty registers its final value more quickly than does lime putty alone and is preferred by some artists.

By adding lime putty to the colors, one adds not only a white but also an increased amount of lime binder, making, in effect, a colored mortar. Such colors may be applied to the intonaco as impasto strokes and will hold their relief well. Heavy impasto application of pigments, ground only in water, will powder off.

6. It is possible to glaze over layers of color containing lime white by going quickly and lightly over them with transparent washes of colors ground only in water. Care must be taken to apply such glazes before the underpainting sets hard and forms a lime crust; otherwise, they may not hold. Conversely, whenever possible it is safer practice to set accents of opaque colors, mixed with lime putty, over transparent washes. These remarks also hold true for painting over mixtures containing Pozzuoli red.

7. Colors such as umber, cobalt violet, and black, which set badly in lime, should be put in while the plaster is still fairly fresh to give them as much time as possible to settle well into the wall. [p. 184]

8. Lime water may be substituted for ordinary water as a thinner for the fresco colors. It is prepared by mixing 4 parts water with 1 part of lime putty. The mixture is allowed to stand until the water separates from the lime. It is then poured off and once more allowed to stand until it is completely clear. Such lime water forms a lime crust and acts as a binder as well as a thinner. Colors mixed with it will dry whiter since the lime water, like the lime putty, acts to some extent as a white pigment.

9. In general, color application should be vigorous and decisive. More quickly in fresco than in other techniques, areas that are worked too long, with no clear purpose in mind, become tormented and muddy in appearance. It is especially important not to stir up the intonaco by aimless reworking with the brush, because the lime will mix with the color and cause streaks.

10. Before it sets, the surface of the picture may be polished by means of a trowel, a metal roller, or a smooth cylindric glass bottle. This gives a greater depth to some of the dark colors. Care must be taken not to do this while the intonaco is so wet as to allow the lime to move and cause streaks.

11. As the intonaco ground becomes drier, the wall begins to suck the color from the brush. This is a sign that carbonation of the plaster is beginning. The intonaco dries, combines with carbon dioxide, and begins to form the lime crust that locks the pigments into the wall surface. Pigment applied over this crust will powder off, and so at that point all painting must cease on the particular section of the intonaco. The drying can be delayed by moistening the wall with a water sprayer. One must take care that the water is absorbed as it goes on, and that it does not make the colors run. Damp cloths hung close to the wall are also used to retard the setting of a section while the painter rests.

12. Before the section of intonaco sets absolutely hard, its outer edges must be trimmed back neatly so that the next section may be joined to it cleanly and firmly. The edge is scored with a sharp tool, and the excess plaster is cut away. The next section is troweled on according to the procedures followed in the section on applying mortar. The surfaces of the cutaway joints, where the new intonaco comes in contact with the old section, must be well brushed with water to insure a good bond. Naturally such joints or seams must be planned so that they fall as inconspicuously as possible. It is also an advantage if these joints do not cut across a large area of uniform color, since it may be very difficult to match the color exactly on the next section of intonaco.

13. As the lime plaster dries, it becomes whiter and the colors on it become lighter. This process goes on for a month or more.

14. Some corrections may be made when the wall is thoroughly dry by using egg tempera, casein paint, or distemper color. Since the wall will continue to change color for more than a month, the longer such retouches are put off, the more closely they may be matched to the final color of the wall. However, all such painting should be restricted to small retouches; the fewer the better. Any extensive corrections should be made by cutting out the intonaco in the faulty area [p. 185] and then replastering and repainting. This should be done while the intonaco can still be cut precisely--that is, within 24 hours.