THE WALL FRESCO

The origins and different processes

The origins and different processes
The fresco is a wall painting executed with the help of pigments of mineral origin (clayey earths, silicates) resisting the lime, soaking to water and applied with brushes, hard or flexible, on a support constituted by a layer of cool mortar, of which the surface composed of sand and extinct lime can be smooth or granular.
Under the action of air, the soluble carbon hydrate exudes by the mortar before turning into a transparent crust of insoluble lime carbonate or calking, that fix and protect the pigments. Due to an abuse of language, the word fresco too often became synonymous of all wall painting.
The technique of the fresco is very old. The works remained in place, since the faraway Aegean time, permit to conclude to the practice of the fresco and techniques that is associated to him.
The technique of the true fresco told "the Italian" or “buon fresco” that require a fast and precise work, is not mentioned really for the first time that in the treaty of CENNINO CENNINI "II libro dell'arte", dated of 1437 that recall the previous practices.

CENNINO CENNINI distinguishes the actual fresco, or application of dilute pigments has water on cool sealer, some so-called technique "has secco" or on dry sealer, mentioned in the treaties of Johann the STUTTERER and monk Théophile, the pigments being coated then in a binder of different nature: to the egg, so-called painting "has moderated"; to oil; to glue; lousy; or even with the water of lime, especially for the colors of "first layer." But, in fact, the painter finishes "has secco" for numerous retouching and some colors, as the bruise. Another technique exists, so-called "has mezzo-fresco", that borrows to the two previous techniques: it consists has apply the pictorial layer on a humid mortar, so that this layer only penetrates superficially. The "fresco-secco" designates a painting has the water of lime on a mortar that took, but that has been washed and dampened of extinct lime added of river sand: the number of hues can be increased there by the addition of casein. This painting to the.
This painting to glue or to the casein is very close to the "secco." Used since the antique, she/it was frequent to the Middle Ages.

It is necessary to put aside the ancient technique of the "stucco-lustro", brilliant stucco, where the use of the marble dust mingled to the lime of the sealer comes closer of the technique of the fresco. After the execution fresco" "has, one smooth the surface painted to the trowel energetically; sometimes, one spread with the help of a brush a solution containing saponifiée of wax; one also conducted a buffing. Work was sometimes completed by a varnishing and a superficial shininess to wax (proceeded used by the Roman and the Byzantine, and known of GIOTTO). According to the cases, the number of layers of sealer and roughcast (mortar of tuileaux ground) could pass three and go until has seven.
The paintings "have frescos" keep their color of origin. The pigments took in the crystalline texture deteriorate only under the actions of the humidity and the chemical substances in suspension in air, provided that the wall of basis is perfectly healthy and exempt of saltpeter.
The execution of the true fresco stays difficult. The painter who works on a humid sealer cannot bring any modifications to his’s project, or to judge the tone of his’s pigments precisely. "When a wall is wet, the colors that one sees are not those that appear when the wall is dry", wrote to the XVIe century Giorgo VASARI. The color of the pigments alters while drying, the brightness of the colors is increased by the presence of the crystals of the mortar: of or requires it to have a "palette of dry tones" as guide. Compared has those of the other techniques of wall painting, the stages of the realization of a fresco are of the most complex and oblige to a continuous work with perfect "splices", at the time of the division in "days" or "giornatte (about 2 per person m2)."

The description given by CENNINO CENNINI in the LXVII chapter of his treaty became classic. The painter covers the masonry with one or two layers: first rough enough roughcast (in general (dry mortar), 2 parts of big sand of river for 1 extinct lime), "I'arriccio" or "arricciato." The sought-after roughness must permit the adhesion of the layer of the final sealer. Then, he sketches the big features of his composition that he delimited before with charcoal while "beating" against the arriccio a rope soaked in the red and tense along the wall. For the complex compositions, this operation can be repeated several times, horizontally and vertically.   
This first sketch is taken then with the help of a "small pointed brush" and a "few of ocher without moderated" liquid. Finished once, "the sinopia" is hidden progressively (the drawing executed with this pigment) under a second sealer of lime, named "intonaco", finely granulated (thinner sand) and thin, with more of lime. The covered surface corresponds has a part of the composition susceptible to be finished the very day where it is undertaken from a second drawing "of piece": the correspondence of these details is assured by the general drawing of the "sinopia", When the fresco is finished, "the sinopia" disappeared completely under "I'intonaco."

of two sorts of moderated: one in whole I'egg added of fig-tree milk, the other to the only egg yolk.
Some changes intervene in the technique of the fresco around 1450. For example, in the Venetian region, the granular final sealer, "pastellon", permitted a better penetration of the painting, sometimes has the limit of "the arriccio": probably to get a resistance superior to the due deteriorations has the saline air.
In the middle of the XVIIe century, the father Ignazio POZZO recommended for the painting to "mezzo-fresco" to return rough "I'intonaco" so that the colors gather more easily to the grains of sand. He/it specified that this practice was destined from afar for the works of big format views. For those seen closely and so that the painting doesn't appear too coarse, it was necessary to apply a sheet of paper and, with a trowel, to flatten the excessive prominences slightly.

After 1450, the process of "the sinopia" lost its importance. More and more, the drawings were drawn on the paper or canvas, to the very measurements of the frescos to achieve. They were reported on "I'intonaco" of the walls according to the method of the "spolvero", from the moment or one had paper and tracings (papers lubricated) more. The plotting makes itself while punching the lines of the drawing with a pin or a tip of bone, while stamping along these lines punched a sachet made of canvas, to very loose fibers, full of coal of wood or "sinopia". 
To this method was added the one of "the impression." The drawing was reported on a thin enough (paper) "cardboard", that one applied on the surface of the humid wall and "printed" with a stiletto while following the lines of the drawing. These two techniques don't constitute the only processes of organization of the shapes at the time of the execution of the frescos. One also meets the use of the grid. The stake to the tile, that goes back up to the antique, permits to pass a small sketch to a big surface and to work directly on the surface to decorate.

THE SUPPORTS
A contemporary artist, who would like to achieve a fresco, will be confronted to big difficulties to find and to prepare the materials. Once, these stains were accomplished by a team of shop helpers.

THE PREPARATION OF THE BOTTOM PLASTER
A quick lime of very good quality is indispensable. This dangerous powder must be stored outside, in a well dug in the earth, and protected of light and impurities by a lid of wood. The lime must remain flooded of pure water and moved has regular intervals during two years, before being sufficiently pure and sleek.
The choice of the sand poses a second problem. The sand of sea or river doesn't agree. The salts that he/it contains cannot be eliminated ever entirely. They would damage the fresco. The sand must not contain a mica. For example, the sand of yard would make disappear the fresco in less than three years. All impurity in the sand will cause the efflorescences, the flakings, the fadings or the chemical reactions. The sand that invites best therefore is the one of a very pure stream.

THE PREPARATION OF THE WALL
Before beginning work, the wall must be prepared meticulously so that it presents the same property of absorption on all its surface. The old plasters and the burnt bricks must be removed and must be replaced. The wall must be perfectly dry and must ventilate, and protected of the sun during work. It is impossible to achieve a fresco on the cement, because it clears chemical impurities. Before applying the bottom, the surface of the wall must be cut with a burin and a hammer, then soaked of clear water. 

THE POSE OF THE BOTTOM PLASTER
Three layers must be applied. The first layer "the trusilar" is composed sufficiently of 3 volumes of clean coarse sand and a containing lime volume of water to make hold the mixture on the trowel with which one will throw plaster on the wall. He will be leveled then rudely with a palette. This layer must make 1,2 cm thick. The second "I'arricciato" layer applies as the first as soon as this one is taken, but is even humid. She must have 6 mm of thickness and must be composed of two volumes of sand and one of lime. The application must limit itself to the surface that will be covered by the work of one day painting. The third "I'intonacco" layer can be put one half-hour later when the second layer is taken but even humid. This final surface must be rinsed with a very weak throw to remove the lime that remains in surface. She is composed of a volume of lime for a volume of sand or, so possible, of marble in powder and its thickness cannot pass 5 mm.

THE PAINTINGS
For the paintings, the chemical composition of the pigments is important certain bus don't combine themselves very well has the lime. The following pigments agree has the fresco: bianco-sangiovanni (pure lime), yellow ocher, yellow of Naples, red of cadmium, Indian red, dead head, ocher red, red potter, green earth, emerald, green cobalt, natural shade earth, brunette ocher, earth of the Périgord (natural and orange), cobalt, céruleum, ultramarine, black oxide of cobalt, oxide of iron and black of manganese.

THE DRAWING OF THE TRACING
Before work doesn't begin, the painter must draw a tracing to the scale of the surface, on which he will indicate the precise localization of the colors that he will use. Every part of the tracing must correspond to the surface to cover per work day. The main contours are drawn through the tracing on plaster with a key of slate in the beginning of every work day. 

THE APPLICATION OF THE COLOR
The painting must be applied with a soft brush in hair of animal. The pigments in powder are diluted to the pure water in saucers and mixed on a palette. The technique of application is to drown the surface then with a light color, transparent like a washing of watercolors, to draw the lines that delimit shapes and contours energetically. It is useful to recall the old Italian principles to model a half-tone with a darker tone, while letting the light tone return the body. He/it can be reinforced with a mere nothing of bianco-sangiovanni, although this pigment is whiter after drying that on the palette. The Italian primitives used the hatchings or shades to model the shapes. modeler les formes.

© Michel GENTY

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