can be noted in the Sola del Constantino in the Vatican
at Rome, one of the stanze or suite of rooms decorated by
Raphael and his associates. There are two figures here painted
on the walls in oil, and though there is a certain depth and richness
of effect secured in this medium, they are too obviously
something added as an afterthought, while the figures in fresco
seem an integral part of the wall.
Work of this kind, finished in each part at a sitting, is what the Italians call buon fresco or “true fresco,” and it has always been, as it was with Vitruvius, the ideal of the art, but at many periods the painters have had to rely largely on retouches and reinforcements after the plaster was dry. Cennino devotes the 67th chapter of his Trattato to a description of the process, and expressly tells us that the method he recommends is the one traditional in the school of Giotto, of which he himself was a direct scion. He is fully alive to the importance of doing as much as possible while the ground is wet, for “to paint on the fresh—that is, a fixed portion on each day—is the best and most permanent way of laying on the colour, and the pleasantest method of painting”; but an ordinary artist of the early part of the 15th century had not sufficient skill to do all that was required at the one moment. Observations made on the works executed by various Italian masters from the 14th to the 16th century show great varieties in this matter of retouching, but the subject need not be dwelt on as it involves no principle. Every painter of worthy ambition, who had entered into the spirit of his craft, would desire to do all he could “on the fresh,” and would be satisfied with, and indeed glory in, the conditions and limitations of the noble technique. Masaccio, even at the beginning of the 15th century, is remarkable for the amount of fine pictorial effect he secured without reliance on retouching. It was second-rate artists, like Pinturicchio, who delighted to furbish up their mural pictures with stucco reliefs and gilding and to add touches of more brilliant pigments than could be used in the wet process. Giotto, Masaccio, Ghirlandajo, Michelangelo, Luini, are among the frescanti proper, who represent the true ideals of the craft.
The following notes upon the methods of the work are derived partly from observation of extant works and partly from the older treatises, but reference has also been made to modern practice in Germany and Italy, as information derived from this last source may be found useful by those who are disposed to-day to make essays in the process.
To avoid loss of time it is essential that the necessary drawing should all be accomplished beforehand. Pozzo, a painter and writer of the end of the 17th century says, “everyone knows that before beginning to paint it is necessary to prepare a drawing and well-studied coloured sketch, both of which are to be kept at hand in painting the fresco, so as not to have any other thought than that of the execution” (First Report, p. 35). In Cennino’s time it seems to have been the practice to square out the work full size from the sketch on to the surface of the rough cast before the intonaco was laid. This at any rate enabled the artist to see how his work as a whole would come in relation to the space provided for it, but the actual intonaco had to be laid piece by piece over this general sketch and the drawing of each portion repeated on the new surface. In the palmy days of Italian painting, however, as well as in modern times, the design has been drawn out on a full-sized cartoon, and this cartoon, or a tracing from it, has been transferred piece by piece to the freshly laid intonaco on which the painting is about to be executed. The drawing may be nailed against the wall, and the outlines passed over with a blunt-pointed stylus of some hard material, that by dinting the paper impresses on the yielding plaster a line sufficient to guide the painter in his work; or the outlines of the cartoon may be pricked and “pounced” with a little bag of red or black powder that will leave a dotted outline on the wall.
The preparation of the intonaco itself is however a matter for much care. The lime should be prepared from a stone that is as far as possible pure carbonate of lime—the travertine of Tivoli, recommended by Vasari, is perfect for the purpose—and after it is burnt should be slaked with water and thoroughly macerated so that the lumps are all completely broken up. The slaked lime, of the consistency of a stiff paste, or as it is termed “putty,” must be kept covered in from the air for a considerable period that varies according to different authorities from eight to twelve months to as many years. All experts, from Vitruvius downwards, are agreed on the necessity for this, but the exact scientific reason therefor does not seem to be quite clear. One advantage of the keeping is that the lime hydrate may take up a certain amount of carbonic acid, though not too much, from the air. Church says that, “not more than one-third or at most two-fifths of the lime should be converted into the carbonate” (p. 19); but Faraday (Fifth Report, p. 25) was of opinion that through lapse of time there was brought about a molecular change that divided the particles more thoroughly and gave the lime a finer texture so as to mix better with the pigments. At any rate, when Cornelius and his associates started the modern fresco revival at Rome, in 1815, an old workman who had been employed under Raphael Mengs directed their attention to this tradition, and they used lime that had been kept in a slaked condition, but still caustic—that is, still deprived of most of its carbonic acid, for twelve years! For mixing the plaster the proportions of lime to sand or marble dust vary; Cennino gives two of sand to one of “rich” or caustic lime, but the Germans used three of sand to one of lime. Whatever its exact constitution, the intonaco has to be carefully laid each morning over that part of the rough cast, previously well wetted, that corresponds to the amount laid out for the day’s work. Contrary to the prescription of Vitruvius and Pompeian practice, which favours a polished surface, the moderns prefer a slight roughness or “tooth” on the intonaco. Painting should not begin, so Cornelius advised (First Report, p. 24), till “the surface is in such a state that it will barely receive the impression of the finger, but not so wet as to be in danger of being stirred up by the brush.”
The pigments are ready mixed in little pots, on a tin palette with a rim round the edge, or on a table, and in old Italian practice each colour was compounded in three shades—dark, middle and light. The water should be boiled or distilled, or should be rainwater; for spring-water often contains carbonate of lime that would derange the chemistry of the process. Again, on account of the chemical action that takes place during the process, the pigments have to be carefully selected. The palette of the fresco painter is indeed a very restricted one, and this is another reason of the broad and simple effect of the work. Practically speaking only the earth colours, such as the ochres raw or burned, can be used with safety; even the white has to be pure white lime (in Italian, bianco San-Giovanni), since lead white used in oil painting (Italian, biacca) is inadmissible. Vegetable and animal pigments are as a rule excluded, “very few colours of organic origin withstanding the decomposing action of lime” (Church, p. 280). The brushes are of hog-bristles or otter-hair or sable, and have to be rather long in the hair. Round ones are recommended. According to early Italian practice, the painter would first outline the figures or objects, already drawn on the plaster, with a long-haired brush dipped in red ochre, and would then, e.g. in the case of the faces, lay in broadly with terre verte the shadows under the brows, below the nostrils, and round the chin, and bring down and fuse into these shadows the darkest of the three flesh-tints, with a dexterous blending of the wet pigments upon a surface that preserves their dampness. On the other side these half-tones are now modelled up into the lighter hues of the flesh. White may then be used in decided touches for the high lights, and the details of the eyes, mouth and other features put in without too much searching after accidents of local colour. Modern frescoists have found that “the tints first applied sink in and look faint, so that it is necessary sometimes to go over the surface repeatedly with the same colour before the full effect is gained” (First Report, p. 24), but it is well to allow in each case some minutes to elapse before touching any spot a second time. For the hair the Italians would make three tints suffice, the high lights again following with white. The draperies are broadly treated. After the whole has been laid in, in monochrome, with the green pigment, the folds would be marked out with the deepest of the three tints for shadow, and these shadows united by the middle tint. Lastly the lighter parts are painted up and finally reinforced with white. The work needs to be deftly touched, for too much handling of one spot may destroy the freshness of the tints and even rub up the ground. It is not necessary (as moderns have sometimes supposed) to put touch beside touch, never going twice over the same ground. So long as the pigments and the surface are wet the tints may be laid one over the other or fused at will, and may be “loaded” in some parts and in others thinly spread, the one essential being that a fresh and crisp effect shall not be lost. The wetness of the ground will always secure a certain softness in all touches, even those that give the strong high-lights, and so important is it that the plaster should not begin to dry, that it should be sprinkled if necessary with fresh water. The characteristic softness of the touches laid on “a fresco” is the more apparent when they are compared with those strokes of reinforcement which may be put on “a tempera” after the work is dry. Armenini says that the shadows may be finished and deepened by hatching, as in a drawing, with black and lake laid on with a soft brush with a medium of gum, size, or white and yolk of egg diluted with vinegar. Such retouches are always hard and “wiry,” and are as much as possible to be avoided.
As examples of execution in fresco no works are better than those of Luini. He painted rapidly and thinly, securing thereby a transparency of effect that did not however preclude richness. Heath Wilson indeed says of his painting that “it may be
