Line drawing of funerary relief of decorators at work. 2nd century. Sens Museum, in Roger Ling, Roman Painting (Cambridge: Cambridge University Press, 1991), p. 215, fig. 234.
The fresco technique of painting involves the application of pigment to a wall surface covered with fresh plaster. While this process might sound fairly simple, it is actually quite complicated. It involves a series of chemical reactions between the materials, which must occur at the correct time in order for the fresco to set properly. Consequently, this technique requires great skill and timing on the part of the plasterer and painter.
Left: Limestone chippings. © iStockphoto/AlasdairJames Right: Painting of a plasterer at work (now lost). Pompeii IX 5, 9. Roger Ling, Roman Painting, 1991, p. 200, fig. 219.
The first step in creating a fresco was to apply the plaster. Most ancient Roman frescoes were made of lime plaster. Lime is a material obtained by burning rocks such as limestone, marble, or chalk. When combined with water, a paste was produced. This paste was mixed with sand or other materials to create plaster, which was applied to the wall in multiple layers of increasing fineness.
Diagram of “giornate di lavoro.” Rome, House of Livia, ‘tablinum’ (south-west wall). Soon after 30 B.C., in Roger Ling, Roman Painting, 1991, p. 201, fig. 220.
Since plaster dries quickly, it was not applied to the entire wall all at once. Rather, the wall was divided into smaller segments that could be plastered and painted within one day. This type of unit is called a giornate di lavoro, or day’s work. The areas where the units joined with one another were disguised by incorporating them into the decorative scheme or the contours of figures or objects.
Left: Red ochre powdered pigment. © Shutterstock/ErickN. Right: Charcoal. ©iStockphoto/Turnervisual.
After all of the required layers were applied, the damp wall was ready for the painter to apply the pigments. Naturally occurring earth pigments were used to create red, yellow, green, and white. Black was obtained from soot or charcoal, while blue was manufactured from several natural materials. Organic dyes, such as purple from the madder herb, had to be mixed with another material, such as honey, prior to application.
Fragment of a Painted Wall, mid-1st century A.D.. Roman. Plaster and pigment; 48.5 x 48 x 8 cm (19 1/8 x 18 7/8 x 3 1/8 in.). Lent by the Field Museum of Natural History, Chicago, 24654.
To apply the pigments, artists used brushes made of natural materials, such as pig bristles. Upon application, the pigments did not merely sink into the plaster. Rather, they were bound to the surface after a chemical reaction occurred between the lime plaster and the carbon dioxide in the air. Consequently, Roman wall paintings made in the fresco technique are very durable, as evidenced by the numerous examples that survived the eruption of Mount Vesuvius.