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Techniques of Fresco | Learn About Fresco
Cennino Cennini, a Tuscan painter who worked in the late 14th and early 15th centuries, described fresco painting in his book Il libro dell'arte. It remains the best technical treatise available. Florence and Tuscany were the principal places where the technique was used and where it was set down in specific rules.
At first, the rules were faithfully adhered to, but as time went by they were partly ignored or modified. One difficulty of fresco painting was that when the plaster is wet, the colors do not look the same as they do when it hardens. The painter could not foresee, except possibly from vast experience, what would happen to the tone of his colors. Another difficulty was the impossibility of correcting mistakes easily, since a brushstroke is immediately absorbed in the top layer of the wet plaster. In case of error, the work had to be destroyed and started anew. Finally, the artist sometimes found himself compelled to save as much time as possible to satisfy the continuously growing demands for his work. Thus, from the middle of the 16th century, some artists turned to the mezzo fresco technique. Others adopted the older and quite different technique of secco painting.
Preparation of the Wall
The work was begun by applying on the selected wall a rough layer of coarse plaster, called arriccio. It was left rough so that the final top layer (the intonaco), on which the fresco was to be painted, would adhere firmly. If the wall already had a suitable layer of plaster, it was not necessary to apply the arriccio, but the existing plaster had to be roughened. This was accomplished by chipping, making a great number of scratches on the surface, and denting it. When the area to be painted was large, the artist had to mark divisions of space. This he did by fastening a fine cord, which had been soaked in red color, at each end of the arriccio and snapping the cord so that it left a red tracing. This procedure was repeated at certain intervals, in both vertical and horizontal directions.
On the arriccio, the artist made what is known today as the sinopia, a large sketch in preparation for the actual painting. It is so named from the special red earth pigment—originally obtained from the town of Sinope on the Black Sea—used to execute it. The sinopia was not a drawing in the true sense but only a transitional, or intermediate, stage in the execution of the fresco. It was meant to synthesize in the best graphic media available all the preceding studies prepared in the painter's workshop.
The artist began by sketching with charcoal the outlines of the painting he planned to make. When satisfied with the charcoal sketch, he went over it with a pale ochre color, then erased the charcoal, and finally reinforced the entire design with sinopia red. At this point he had achieved a full-size plan of his work. From it he could draw the necessary conclusions in relation to his future work a fresco and could, if necessary, consider changes. At the same time the patron, who by now had a clear idea of how the artist had interpreted the theme and had carried out his commission, could ask for changes if he were dissatisfied.
After completing the sinopia, the artist proceeded to the actual painting of the fresco. On a large surface it would not be possible to keep the top layer, or intonaco, wet for the time required for the completion of the whole work. Therefore, the artist proceeded by giornate, or daily work units. That is, he spread on the arriccio only as much wet plaster as he needed for the amount of work he intended to execute each day. Although a section of the sinopia disappeared under each day's new plaster, the artist rapidly retraced its essential lines and carefully finished painting that part of the fresco before nightfall. The other parts of the sinopia, in the areas that remained uncovered, served as a guide and as a reference for the proportions of the painting.
The various giornate can still be distinguished on the surface of a fresco. Work usually was started from the top and carried on toward the bottom. The sequence of each day's work may even be established, since the wet plaster that was spread later overlaps the section previously applied along the line where the layers meet. At the bottom of each day's section, the layer of intonaco was applied with gradual diminution of thickness to make a smoother joining.
Direct Transfer of Paper Drawings
The use of the sinopia was prevalent until the 1440s. Thereafter, drawings of the same size of the fresco to be executed were usually made on paper. They were transferred to the wet plaster by two methods—the spolvero (dusting or pouncing) method, which was most popular during the period 1450–1500; and the cartone (cartoon) method, which was frequently used during the 16th century.
With the spolvero method the outlines of the drawing were pricked through the paper with a needle. The drawing then was cut apart in sections corresponding to a day's work, and a section was placed on the freshly laid intonaco. The artist then took a "pouncing bag"—a loosely woven linen sack filled with charcoal powder—and passed it along the outline of the drawing. The charcoal powder, slipping through the holes in the paper, left a clear dotted outline, which served as a guide to the painter and which on close examination is still visible today.
The cartoon method simplified and accelerated the transfer of the drawing to fresh plaster. The drawing, called a cartone (cartoon), was made on paper of medium thickness and then cut apart. A section was placed on the intonaco, and the outline of the design was incised through the cartoon with a sharp stylus, producing a groove that served as a guide for the artist.
There was—and still is—another method of transferring a drawing from paper to wet plaster. This was the "net," or quadrettatura, method, which made it possible for artists to enlarge a small drawing to large dimensions. The surface of the drawing was divided by horizontal and vertical lines into equal squares. A similar net—grid, or squaring, as it was also called—was traced in full scale on paper or light pasteboard. The lines of the drawing then were enlarged freehand in each square, as is done today mechanically with the pantograph. Records of the use of this method go back to the late 14th and early 15th centuries, but many artists who had always drawn their large compositions freehand opposed the net method as being almost mechanical and therefore degrading.