A great era, a timeless classic, an introduction to the knowledge of Italian Renaissance wet frescoe
Wet fresco has a long history, having first become popular in ancient Egyptian times. in the Mediterranean the method was introduced in 1650 BC by the Minoan civilisation of Crete in Greece. Renaissance wet fresco painting began in the thirteenth century with Cimabue, whose student Giotto di Bondone (1266-1337) was the first artist to use the formal method, and after almost a century of refinement and innovation, wet fresco was well established before the heyday of Michelangelo and Raphael.
Wet fresco (fresco, Italian for 'fresh') is a fresco technique that can be understood as a process of mixing pigments with the wall and carbonising them, and is the most durable of the known painting methods. Due to the nature of wet frescoes being completely integrated into the wall, and thanks to the use of modern wall veneer unmounting techniques, the surface of the painting can also be transferred to a linen surface or other material for better restoration and conservation, and after restoration and painting, can be displayed in a wider range of spaces.
Wet frescoes have many incomparable advantages: they are resistant to peeling and cracking, have a non-reflective surface, are rich in colour layers, have a unique effect of transparency, and have a delicate texture particularly suited to long-term monumental requirements, and the work becomes more valuable with age.
The vast majority of pigments used in wet fresco are derived from natural minerals and some plants and undergo a process of careful grinding and high temperature calcination before being stored and used in powder form. Before the painter can paint, the pigments are mixed with a binder to form a powdered suspension, usually made from egg wash, animal and vegetable oils and refined natural gums; in addition to these binders, some artists also use other substances such as animal blood. It is said that Leonardo da Vinci invented a special pigment when he created The Last Supper, and it was later discovered that it was actually the bile of a cow that was added to it, as it has the effect of emulsifying fats and oils quickly, and therefore blends the pigment more evenly and gives a better expression of colour.
Here is a brief introduction to some of the colours commonly used in wet fresco.
The red pigments were mainly hematite containing trivalent iron ions, as well as cinnabar and red coral; the blue-green pigments mainly contained copper, including lapis lazuli, stone green and lapis lazuli, etc. It is worth mentioning that blue-green pigments were very expensive at the time, and the raw materials were mainly concentrated in the Afghan region of Central Asia, where the price of an equivalent amount of lapis lazuli was said to be even higher than that of gold, so by looking at the amount of blue-green (ultramarine) pigments used by a painter, one could The famous Venetian painter Bellini even went so far as to paint the background of a portrait of a nobleman cobalt blue without any treatment; yellow pigments are mainly sulphides, such as staghorn and plant-based garcinia and iron-bearing clay; white pigments are mainly compounds containing lead, although they turn dark brown when oxidised. The main reason for the brown colour of many of the figures in our Dunhuang murals is that lead white was used as the base colour and then mixed with cinnabar to create the tone and texture of flesh powder on the skin, but eventually it all oxidised to a dark brown.
In addition to the rarity of the raw material, the production process is also complex and difficult, for example, the lapis lazuli mentioned earlier, to make it into ultramarine it must first be ground into powder, the degree of fineness of the grinding can also determine the difference in colour, for example, the coarse powder will appear dark blue, while the fine one is light blue, then add a series of binders such as paraffin, resin and animal oil until it is mixed into a homogeneous mud, then put into a linen bag in hot lye and repeatedly Knead until the colour precipitates, replace the alkali solution when it is saturated and repeat the process until no more colour precipitates. These suspensions are then left to settle and the powder is ultramarine. It is the most saturated at the beginning and therefore the most expensive. A quick tip: it is possible that painters of the time were tempted to pass off cobalt blue containing manganese oxide or iron oxide, which oxidises to a dark green colour over time, for profit.
Afghan Lapis Lazuli
It should be added that the blending agents added to wet fresco pigments are animal oils and fats so that the powder is insoluble in oil, but if vegetable oils are added, the powder forms a solution rather than a suspension, and the final product is the dye used as a stain.
Walls and the painting process
The process of creating a wet fresco is time-consuming and technically demanding, usually beginning with the laying of several layers of plaster base with quicklime and sand. Although the method of creating a wet fresco has undergone many changes, a wet fresco is usually completed in several stages: a rough, coarse coat of plaster known as a trullisatio, followed by a second coat of plaster (arriccio), which is also thicker and rougher, then a buffing layer (arenato), and finally a coat of The final coat of lime plaster, or intonaco, is applied before it dries.
The sketches of the composition (sinopia, full-size sketches) are transferred to the wall after the polishing layer, and the painting layer is then divided into sections (called giornate, Italian for "working day") to cover the sketches smoothly, according to the size of the area the artist wishes to complete within a certain time frame. To ensure the effect, the artist must have completed an equal scale base beforehand, on which he makes a grid to divide the picture into squares of the same size, which are then transferred to the wall one by one. The artist must paint very quickly, as once the plaster has dried it is no longer able to absorb the paint. Any layers of paint that are not painted within a certain time must be removed so that fresh plaster can be applied on the next working day to continue the painting.
The size of the wet frescoes is usually so large that they are painted on scaffolding, usually in a top-to-bottom sequence, with horizontal strips of approximately 1.2m to 1.8m at a time. When one layer is completed, the scaffolding is lowered one layer.
Too thin paint and too wet a wall will result in a halo of colour or too light; too dry paint and an excessively dry wall will result in the paint not penetrating the water; the right consistency of paint is applied to the freshly laid plaster base , as the colour is absorbed by the surface of the wall as the plaster dries, wet fresco is one of the most durable painting techniques, and it is the essence of wet fresco. Wet frescoes in some medieval churches that have been in stable condition for centuries, proving the longevity of the method. The colours of the pictures have also remained vibrant thanks to the use of pigments that are less prone to chemical reactions by the artists. In addition to this true wet fresco (buon fresco), the artist also used the technique of dry fresco (fresco secco). Dry fresco is painted on an already dry plaster base. Although the finished work is visually similar to a wet fresco, the colour is not absorbed into the wall but merely adheres to the surface, so dry frescoes do not last as long as wet frescoes. This is illustrated, for example, by the contrast between the current state of Michelangelo's Sistine zenith, painted in wet fresco, and the current state of Leonardo da Vinci's Last Supper, executed mainly in dry fresco.
The whole process of wet fresco is explained by a chemical equation: quicklime (calcium oxide) is first mixed with water and stirred to produce calcium hydroxide; the calcium hydroxide is exposed to air and dehydrated and combines with carbon dioxide to form calcium carbonate, which is insoluble in water, so the artist has to complete the work before the wall turns into calcium carbonate, so to speak, in a race against time, but also requires excellent skill in the hands and good control and the big picture, so there are very few truly outstanding masters of wet fresco in the Renaissance era.
CaCO3 → CaO + CO2
CaO + H2O → Ca(OH)2
Ca(OH)2 + CO2 → CaCO3 + H2O
The first is for the most detailed parts, such as the face of the figure, for which the artist first pokes holes in the sketch with a nail or other sharp object, then fixes the paper to the wall and taps it with toner to leave marks in the holes; the second is for parts that do not require much detail, such as folds of clothing and other scenes, for which an iron pen is used directly to scratch through the lines and leave marks on the wall, which is not yet completly dry.
Repair & Protection
Although wet frescoes are the longest lasting type of painting, because they are integrated into the wall, they can be easily destroyed if the building is damaged or even destroyed. Wet frescoes are only suitable for interiors, where polluted outdoor air and wind-borne particles can also flake the surface, so the vast majority of wet frescoes are created in indoor spaces. Over the years disasters such as war, earthquakes, fires and floods have all had a significant impact on wet frescoes. With the advent of technology, modern museum professionals have invented conservation techniques that allow wet frescoes to be removed from walls and transferred to frames, such as the method used to preserve many wet frescoes in churches in Florence when the Arno flooded in 1966.
To transfer a wet fresco, a corresponding opening is first cut around the wall, then a canvas-like material is glued to the surface with a hydrosol, and finally this part of the fresco is transferred from the wall glass to the new support medium. Watch the video below to get a better idea of how wet frescoes are preserved and restored.
Finally some climatic and geographical constraints of wet fresco are given. Italy is located on the Apennine Peninsula and has a typically Mediterranean climate, also known as a subtropical summer dry climate. As the name suggests, the main characteristics of this climate are hot, dry summers and mild, rainy winters. The advantage of this climate, however, is that there is no extreme cold weather in winter, with average temperatures ranging from 4-10°C, so it is not easy to freeze, which creates favourable conditions for the creation of wet frescoes, but because of the mountainous nature of Italy there are also significant temperature variations, as Michelangelo experienced when he painted the Sistine zenith.
In addition, extremely humid areas are not conducive to the creation of wet frescoes, so one area of Italy that is particularly unsuitable for wet frescoes is the watery city of Venice, where excessive humidity can seriously impede the drying process of plaster. As a result, Venice has hardly produced any famous wet fresco masters.
In the centuries following the Renaissance, wet frescoes became less popular for a number of reasons. The most important of these was the fact that wet fresco no longer met the needs of the times and its social function was significantly diminished; secondly, the availability of more convenient and cost-effective oil paints was favoured by artists and the limitations of wet fresco became apparent; and, of course, the loss of a number of masters led to the loss of the craft, although this was not a decisive factor.