It was Cennino Cennini author of the Libro dell’Arte, who described the method known as “fresco.” According to him the artist must apply his pigment on the damp or fresh (fresco) intonaco immediately that it has been placed on the wall. The pigment penetrates the wet plaster, and after drying and hardening, it will solidify and unite with the plaster. However, when the artist paints on dry (secco) intonaco, it is necessary to use a binding medium such as glue to hold the pigments together, in order to cause them to adhere to the wall’s surface. Before Cimabue’s time, wall paintings were mostly painted a secco, but from the first Florentine painters to Michelangelo, the wall painting was true fresco. During Cennini’s time, plaster was “spread thin, but not too thin, and perfectly flat.” This had advantages: rain runs quickly off a smoothly painted surface, but not a rough one. For secco painting, plaster should not be smooth, since colours held together by binding adheres better to a rough surface. Later, the intonaco was “granulated,” covering it with minute particles of sand, to aid the sticking of the colours. Colours used when painting a fresco were earth colours, easily distributed, which can sink into the wet plaster; but the only types of blue known to early painters lapis lazuli (ultramarine) and Alemagna blue (azurite) weren’t completely soluble. So these colours were applied to the wall a secco, held together by glue. Some of these were re-touched in tempera, but nearly all of these additions have vanished. As Procacci states, it is important to identify the reasons why true fresco was abandoned by artists in favour of secco which was “aesthetically less satisfying”, and also less immune to the ravages of time and climate. Firstly, artists using damp intonaco could not see the exact tone of the colours; they were “working in the dark” Secondly, mistakes in drawing in true fresco cannot be accommodated because they can only be corrected at the beginning of the work, not later when the brushstroke has been absorbed by the intonaco. Lastly, and most importantly, a secco was faster, and artists were under increasing pressure to achieve their deadlines set by impatient patrons and organisations.
Some Useful Terms. (Procacci).
Arriccio – rough layer of coarse plaster, with uneven surface.
Intonaco- upper level of plaster, sometimes used as the arriccio.
Giornate- sections of frescoes corresponding to a day’s work.
Pontate- division between sections determined by the level of the scaffold.
Spolvero- pouncing or dusting the chalk or charcoal, eventually replaced by cartoons.
Stacco. Term used in restoration. Process of detaching all the intonaco, first used in 1374; used for well-preserved frescoes where the colour and intonaco are unified and not easily divisible. Achieved by use of a knife and pounding the intonaco with a wooden or rubber hammer to reduce adhesion. Fresco is then laid down on a flat surface with the canvas still attached, and the intonaco is removed from the back until the thin layer of paint is reached; when the layer of paint is smooth and clean, it is glued to a support and mounted; the canvas is then removed from the fresco.
Strappo. Term used in restoration. Process of removing the paint-layer alone; used for disintegrating surfaces where the colour has started to detach itself from the intonaco; used to save works which have been affected by corrosive salts. Canvas gradually pulled off wall, bringing with it the layer of colour. The fresco is then laid flat, and as with stacco method , all the intonaco is removed until the surface is smooth.
Taddeo Gaddi, Madonna del Parto, fresco, possibly 1350s, Florence, 140 x 85 cm,Church of S. Francesco di Paola.
Fresco technique: smooth intonaco, detail from a fresco by Giovanni da Milano in the Rinuccini Chapel, Santa Croce, Florence.
Fresco technique: rough intonaco, detail from a fresco by Bernardino Poccetti in the Giglio Chapel, Santa Maria Maddalena dei Pazzi, Florence.