The fresco technique
1) What is the fresco technique
The fresco is an ancient painting technique achieved by painting on fresh plaster with pigments diluted in water: in this way, once the plaster has settled, the color will be completely incorporated, thus acquiring a particular resistance to water and time.
2 ) It consists of three elements :
3) • The support, made of stone or brick , must be dry and without irregularity .
• Before applying the plaster, the surface is prepared with the “arriccio” , a mortar made from slaked lime or lime putty, coarse sand of the river or , in some cases pozzolana sand and, if necessary, water, applied in a thickness of about 1 cm, in order to make the wall as uniform as possible.
4) • The plaster (or ” tonachino ” or ” intonachino ” ) is the backbone of the entire fresco .
• It’s composed of a mix made with fine sand, marble powder, sifted pozzolana , lime and water.
5 ) The color , which is necessarily applied on the plaster still wet (hence the name “fresco ” ), is of mineral nature, since it must resist the alkalinity of lime .
6) The main difficulty of this technique is that it does not allow second thoughts : once left a mark of color, this will be immediately be absorbed by the plaster; the short time of realization complicates the work of the fresco painter, in fact the carbonation occurs within three hours the lying of the plaster.
To overcome this problem, the artist will create small portions of the fresco ( days ) .
Dry corrections are possible, that is by tempera applied on the dry plaster: they are, however, more easily degradable .
7) Another difficulty is to understand what the actual shade of color will be: the wet plaster, in fact, makes the colors darker, while the lime tends to whiten the colors. To work around this problem, you can try to run a test on a pumice stone or a piece of paper left to dry in the open air or Scirocco wind, ie hot air.
8 ) Given the technical difficulties of a good realization, this painting technique is now in disuse, while in the past centuries was very popular.
9) The realization of a fresco requires rapidity: a hesitation on the drawing will cause a waste of valuable time and correction possibilities are very limited.
It is therefore necessary that everything is ready before starting the work: both in the author’s mind and on the wall.
10) – Start by drawing a sketch on a small scale .
– Search the harmonies of colors for the whole composition .
– Draw on real scale with a charcoal on large sheets of paper, or on molds joined together with adhesive tape.
– If the painting is very large, make a piece a day.
– On the drawing on real scale use the white color to determine
the position of the clearings .
11 ) – Before starting the transfer of the mold, wait until the plaster is dry enough to withstand the pressure of a finger.
– To trace the lines, which are needed to frame the draw and determine its exact location on the wall, it’s used a rope dipped in paint like a rubber band stretched between two points of reference, which leaves a trace of color on the plaster.
– The technique of transferring the draw on the support is called cast engraved. With the handle of a brush you draw the lines of the paint through the paper by pressing lightly, without going too deep, so as to leave a slight track on the fresh plaster.
12) The realization of the fresco requires a good organization: make sure that the colors and brushes are all at handy on a table or on a stable work surface; arrange various vases with clean water to wash the brushes, prepare in advance the different colors and their clearings in labeled jars, start working from the top to prevent smudging .
13) While painting one must have in mind that the background will tend to stand out with light colors and the plaster, that is grayed out when it is wet, will be white once dry and will lighten the shades.
Practice on paper to get an idea of the colors once dry.
14) Colors compatible with the fresco painting
Not all pigments can be used in fresco painting.
In fact the causticity of the lime ‘ attacks ‘ certain pigments and in some cases completely alters the color characteristics .
The pigments not compatible with the lime can be used on dry surface or mixed with the organic binder and applied on the wall surface when the carbonation process is completed.
15) How to distinguish a fresco painting from a fresco-secco painting (dry paint)
Some simple observations can be of help.
If these are not enough you can resort to laboratory analysis.
Elements to note:
• Brightness and durability of colors .
A color applied with the fresco technique usually appears brighter due to the recrystallization of calcite on the surface.
The veil of calcite is also responsible for the durability that the frescoes usually have. These elements alone, however, are not discriminating .
16) • Limited color scale .
In the fresco paintings some types of pigment can not be used because once in contact with lime they change.
Only a rather limited range of colors can be used in the frescoes .
This is the reason why , when desired, to enrich a painting with a wider variety of colors, it is necessary to paint some portions with the fresco-secco painting technique ( applying the color on dry plaster ).
17) Mode of deterioration.
Where there is a missing spot ( for degradation ) of dry color it’s possible to observe the smooth surface of the plaster on which it was lying .
In the case of a fresco where there are detachments and falling parts of color also few mm or tenths of a mm of plaster are incorporated (this is because the color penetrates in depth ) .
The surface , watched closely , will then appear wrinkled and faded at the same time .
By sliding a finger over it , some granules will easily detach.