On this page: Support (Wall and Plaster) | Fresco Colors | Secco Finishing
Fresco painting is a type of mural painting that reached its greatest flourishing in Italy between the 14th and 16th centuries. The distinctive feature of this technique lies in the use of the work’s very support, the wall itself, or more precisely, the lime in freshly applied plaster, as the binding medium (hence the name pittura a fresco, meaning “painting on fresh [plaster]”).
CHAPTER V. (XIX.) Of Painting on the Wall, how it is done, and why it is called Working in Fresco.
[…] Of all the methods that painters employ, painting on the wall is the most masterly and beautiful, because it consists in doing in a single day that which, in the other methods, may be retouched day after day, over the work already done. […] Many of our artists excel in the other kinds of work, that is, in oil or in tempera, but in this do not succeed, fresco being truly the most manly, most certain, most resolute and durable of all the other methods, and as time goes on it continually acquires infinitely more beauty and harmony than do the others. […]
Giorgio Vasari (1511-1574), Vasari on Technique; being the introduction to the three arts of design, architecture, sculpture and painting, prefixed to the Lives of the most excellent painters, sculptors, and architects
When exposed to air, the slaked lime in the plaster begins to harden, returning to a stable crystalline form, locking the colored pigments into the surface and integrating them with the wall structure, a transformation that ensures the durability, luminosity and color saturation of true fresco.
In modern chemistry, this process is called carbonation (Ca(OH)₂ + CO₂ → CaCO₃ + H₂O): in the case of fresco, calcium hydroxide (lime) reacts with carbon dioxide from the air to form calcium carbonate (chalk) and water, which subsequently evaporates.
When we think of frescoes, we inevitably picture the walls and ceilings of Renaissance churches and palaces in Italy. But it is important to remember that this kind of wall painting is neither exclusively Italian nor uniquely Renaissance. Although techniques varied greatly across time and region, the same pigment binding principle has been employed since antiquity. Forms of lime-based wall painting were practiced in ancient Greece and Rome, and also appear in India, Central Asia and western China, where similar principles were adapted to local materials and traditions.
Preparing the Wall for Painting
Preparation of the plaster and its layering on the wall
The terminology (and the technology) still used today by fresco practitioners in Italy is the same as that used during the Renaissance. Detailed descriptions of wall preparation can be found in the writings of both Cennino Cennini and Andrea Pozzo, but it is Leon Battista Alberti, in his Ten Books on Architecture, who offers the most complete account of the three layers of plaster and their respective functions.
BOOK VI. CHAPTER IX.
In all incrustations there must be at least three coats of mortar; the first is called rough-casting [Rinzaffare], and its office is to stick as close as possible to the Wall and to bind on the two outer coats; the office of the outer coat [Intonico] is to make the work shew neat, smooth, and polished; that of the middle coat, which we call plaistering [Arricciare], is to prevent any faults or defects in either of the other two.
[…]
The first of these should be very sharp, and made of pit sand and brick beaten not too fine, but about the size of small gravel, and laid on about the thickness of three inches.
For the plastering, or middle coat, river sand is better and is less apt to crack. This coat too should be somewhat rough, because to a smooth surface nothing will stick that you lay on.
The last of all should be as white as marble; for which reason, instead of sand you should use the whitest stone that can be got pounded small; and it will be sufficient if this coat be laid on about half an inch thick, for when it is much more, it will not easily dry.
Leon Battista Alberti, Della architettura di libri X; Della pittura libri III; e, Della statua libro I: tradotti in lingua italiana
The three plaster layers as they are also known today are:
Rinzaffo (rough coat):
This is the first plaster layer, applied directly onto the masonry. Its function is to create a strong bond with the wall, level the surface and provide a grip for the layers above. It is made of coarse materials, typically coarse sand and crushed brick.tile (coccio pesto) mixed with lime in proportion 2-3 parts filler to 1 part lime. Alberti recommends a thickness of about three inches. It must be applied to a thoroughly wetted surface and left rough to ensure adhesion.
Arriccio (floating coat):
The second layer levels the surface further and provides a uniform foundation for the design. It is made from aged slaked lime and clean river sand in proportion 2 parts filler 1 part lime. This coat is also applied to a wetted surface and must remain somewhat rough. Once dry, the full-scale cartoon or drawing is transferred onto it using methods like pouncing or incising. A preparatory drawing with sinopia and compostional grid is made on this layer.
Intonaco (painting coat):
This is the final, thin layer of fine plaster onto which the painting is done while the surface is still wet. It is made with clean and finely sieved river sand and/or crushed white stone mixed (marble dust for example) with well seasoned slaked lime, worked to a creamy consistency (grassello di calce). In this case the proportions of the plaster are 1 part filler to 1 part lime. The plaster is applied very smoothly only to the area that can be painted in a single day (a giornata), and pigment must be applied while the surface is still moist to ensure chemical bonding.
Let’s do some Alchemy!
Ingredients to make the fresco plaster:
CALX
Grassello di calce is a traditional Italian building material made by slaking quicklime (calcium oxide) in excess water, then allowing it to age and mature into a smooth, creamy paste.
This kind of slaked lime, also called lime putty, becomes highly workable and is used in fine plastering, fresco painting, and stucco work. Its slow carbonation and high plasticity make it ideal for durable, breathable finishes in historical and artistic applications.
ARENA
River sand in fresco work refers to sand collected from riverbeds, valued for its rounded grains and purity. Its smooth texture and low salt content make it ideal for mixing with lime to create stable, fine plasters that bond well to walls and resist cracking.
AQUA
Clean water, typically rain or spring water was used. We use distilled water where possible, but in fresco painting, where big quantities of water are required it is ok to use clean tap water.
Additional ingredients:
- Coccio Pesto is crushed terracotta or brick mixed with lime to create a stronger plaster.
- Straw, vegetal fibers (also paper pulp) are added to coarse layers of plaster for tensile strength, reduce cracking and slow down drying speed allowing longer painting time.
- Pozzolan: is a volcanic ash extracted near Pozzuoli in Naples, it is added to lime to improve strength and water resistance in plaster.
- Marble Dust is finely ground marble used to whiten and smooth the final plaster layer in fresco.
The Colors of True Fresco
Pigments suitable for painting in true fresco
Today, we are fortunate to have a fairly clear understanding of the materials used by the masters of the past in fresco work, thanks to both historical texts, such as Cennino Cennini’s Il Libro dell’Arte or althogh much later, but still invaluable brief guide to fresco in Andrea Pozzo’s Perspectiva pictorum et architectorum, as well as to the material evidence gathered over recent decades through scientific examination of wall paintings.
Due to the alkaline nature of lime (very high pH ≈12–13), continuous exposure to light, and the absence of protective varnish, fresco painting permits only a limited range of pigments that must remain chemically stable in an alkaline environment, primarily ochres and other earth pigments, iron oxides (mars pigments), and silicates. Both Vasari and Armenini suggest using only earth pigments and lime white for the true fresco process:
BOOK TWO. CHAPTER VII
On the true precepts of the art of painting by Armenini, Giovanni Battista, 1533?-1609
First, as is known, artificial colors never work well in fresco, and there is no way of making them endure, especially in the open, because they require very dry surfaces and dry places; […] But in using colors a fresco, keep in mind that, as has been said, the wall desires only natural colors born from the earth, for there are different types of earth, each with its own color. I believe that these are commonly known throughout Italy. Natural colors are ground finely with pure water, except smalto and other similar blues. For the white used in fresco, as one knows, one takes the best of the whitest lime […]
CHAPTER V. (XIX.) Of Painting on the Wall, how it is done, and why it is called Working in Fresco.
[…] To prevent this the wall that is to be painted must be kept continually moist; and the colors employed thereon must all be of earths and not metallic [non di miniere, not from a mine] and the white of calcined travertine [travertine is a lime stone of a good quality, therefore Vasari indicates a specific kind of lime white].
Giorgio Vasari (1511-1574), Vasari on Technique; being the introduction to the three arts of design, architecture, sculpture and painting, prefixed to the Lives of the most excellent painters, sculptors, and architects
This general approach is confirmed by present day scientific examination of frescoes by one of the greatest artists who worked in this technique, Michelangelo Buonarroti. Gianluigi Colalucci, the restorer of the Sistine Chapel lists the following pigments employed by the artist:
Michelangelo, who in his youth had attended the workshop of Ghirlandaio, shows thorough knowledge both in his use of the fresco technique and in his choice of pigments all of excellent quality, selecting those suitable for fresco painting and discarding any unsuitable ones. Consequently, it can be noted there is a lack of copper-based pigments and a minimal use of lead-based pigments. The color range is as follows:
Colalucci, Gianluigi. 2016. “Michelangelo Buonarroti: Restoration of the Frescoes on the Vaulted Ceiling and the Last Judgment in the Sistine Chapel”. Conservation Science in Cultural Heritage 16 (1):89-126. https://doi.org/10.6092/issn.1973-9494/7166.
- ‘bianco di San Giovanni’ (a white obtained using air-dried hydrated lime which is then ground; the procedure is repeated at least three times);
- vine black;
- ivory black;
- mars brown (iron oxide); umber (iron oxide, manganese dioxide and clay silicates);
- burnt sienna;
- yellow ochers (iron oxide hydrate); raw sienna;
- red ochers; rarely cinnabar, rarely minium;
- green earth (iron silicate);
- smalt (cobalt glass);
- lapis lazuli (aluminum silicate containing sulfur).
You can now explore most of these colors, along with the rest of the Renaissance palette, in the Historical Colors section of Ars Pictoria. Additional entries, including smalt and lime white, are currently in preparation and will be published soon.
Notably, Michelangelo used minium (red lead) only in the initial sections he painted, such as The Flood, and abandoned it shortly thereafter. It also appears that he employed cinnabar (mercury sulfide), a pigment generally considered incompatible with true fresco. Nevertheless, both ancient Roman painters and later artists such as Andrea Pozzo developed methods to incorporate this toxic and unstable yet exceptionally vivid and beautiful red pigment into fresco painting.
Cennini, as cited below, offers a similar list of pigments. Additionally, he mentions an artificial color, giallorino, which most likely corresponds to the lead-based pigment known today as lead-tin yellow, referred to as massicot in Northern European texts:
THE WAY TO PAINT ON A WALL IN SECCO; AND THE TEMPERAS FOR IT. CHAPTER LXXII
Those [colors] which can be used in fresco are giallorino, lime white, black, ocher, cinabrese, sinoper, terre-verte, hematite. The ones which are used in fresco call for lime white as an adjunct, to make them lighter; and the greens, when you want to keep them as greens, call for giallorino: when you want to leave them as sage greens, use white.
The craftsman’s handbook by Cennini, Cennino, active 15th century; translated by Thompson, Daniel Varney, 1902- ed
Some lead-based pigments are relatively stable in fresco but are toxic and appear only rarely in works executed entirely in true fresco. Therefore, due to toxicity and questionable stability, minium, giallorino and cinnabar are not recommended for use in buon fresco technique.
Today, a wider range of pigments is available that are considered relatively resistant to the aggressive alkaline conditions created by lime. These include many synthetic oxides, such as those based on iron (mars), chromium, titanium, and manganese. Cobalt pigments, especially cobalt blue, are generally regarded as stable in fresco, cadmium pigments are also used by some practitioners and are known for their good lightfastness, though their long-term stability in fresco remains debated.
Let’s summarize the colors that were historically used in fresco painting, and those that can be used today to build a reliable buon fresco palette (color indexes are added where possible to help you find correct pigments in stores):
| Color: | Historical Pigments: | Modern Pigments stable in fresco: |
| White | lime white (bianco San Giovanni) | titanium white (PW6) |
| Black | vine black (PBk7), ivory black (PBk9) | mars black (PBk11) |
| Yellow | yellow ochre (PY42), raw siena (PY42) | there is a big range of iron oxide yellows (PY42 and PY43) which includes most yellow ochres/earths , mars yellows, giallo dorè and others |
| Red and Orange | hematite, red earth/sinopia (PR101), burnt sienna (PY42 + PR101) | mars red (PR101), mars orange (PY42 + PR101) |
| Green | green earth (terra verde, PG7 + PG8) | chromium oxide green (PG17), possibly viridian (PG18, not viridian made with phthalo) |
| Blue | smalt (less stable than cobalt blue), natural ultramarine (lapis lazuli) | ultramarine (PB29), cobalts (PB28), cerulean blue (PB35), possibly Prussian blue (PB27) |
| Violet | morellone, caput mortuum (PR101 variants) | manganese violet (PV16), cobalt violet (PV14) |
| Brown | natural umber, burnt umber (variants of PBr7 or PY42+PR101+PBk11) | mars brown (PBr7), chromium oxide brown (PBr24) |
The Secco Finishing
Pigments and binders used in final glazes painted on a dry plaster
Fresco, although regarded by Renaissance artists as the most noble and the most technically demanding form of wall painting, was not the only technique in use. In contrast to painting on fresh plaster, artists often worked a secco, on dry plaster, using a range of binding media such as oil, glue, casein, and egg tempera. In some cases, they even used slaked lime itself, mixed with pigments, to paint directly onto dry walls.
Since the early days of wall painting, artists often combined a fresco and a secco techniques, completing a composition begun on fresh plaster with glazes or final touches applied a secco, using media such as glue or egg tempera. Some pigments (such as azurite, vermilion or lake for example) would be altered or damaged by the strongly alkaline lime and were typically applied on top of a dry underpainting executed in buon fresco. Cennino goes in a great deal of detail explaining which pigments can be employed in fresco and which only on dry plaster. Unfortunately, this combination of fresco and a secco techniques is not as durable as true buon fresco, since pigments applied with organic binders tend to detach from the smooth, polished plaster surface, and may darken or fade over time.
THE WAY TO PAINT ON A WALL IN SECCO; AND THE TEMPERAS FOR IT. CHAPTER LXXII
You may use any of those colors which you used in fresco in secco as well; but there are colors which cannot be used in fresco, such as orpiment, vermilion, azurite, red lead, white lead, verdigris, and lac. […] Those colors which cannot be used in fresco require white lead and giallorino as adjuncts, to make them lighter, and sometimes orpiment: but orpiment very seldom.
The craftsman’s handbook by Cennini, Cennino, active 15th century; translated by Thompson, Daniel Varney, 1902- ed
Regarding the kind of binder (tempera) for secco painting, Cennini recommends two options: either the whole egg tempera or egg yolk only:
THE WAY TO PAINT ON A WALL IN SECCO; AND THE TEMPERAS FOR IT. CHAPTER LXXII
There are two good kinds of tempera for you, one better than the other. The first tempera: take the white and yolk of the egg; put in a few clippings of fig shoots; and beat it up well. Then put some of this tempera into the little dishes, a moderate amount, neither too much nor not enough, just about as a wine might be half
diluted with water.[…] The second tempera is simply yolk of egg; and know that this tempera is a universal one, for wall, for panels, or for iron; and you cannot use too much, but be reasonable, and choose a middle course.
The craftsman’s handbook by Cennini, Cennino, active 15th century; translated by Thompson, Daniel Varney, 1902- ed
The very expensive natural ultramarine (lapis lazuli), that could be used in true fresco, was often replaced with azurite blue pigment applied a secco due to its incompatibility with lime. An underpainting was usually executed a fresco, often using morellone, a violet-brown pigment. Although azurite retained its vibrant blue color, the layer of glue or egg based paint applied on dry plaster frequently flaked off over time, revealing the fresco underlayer beneath.
Giorgio Vasari, drawing inspiration from Michelangelo’s masterfully executed frescoes in the Sistine Chapel and relying on his own deep familiarity with the technique, strongly advocates for executing the painting entirely on fresh plaster. Cennini likewise emphasizes that the strongest tempera, that is, the most durable bond between pigment and wall, is achieved by painting on fresh plaster.
Nevertheless, primarily due to color palette limitations, many notable painters, including even buon fresco experts, such as Michelangelo, Raphael and even Vasari himself, employed other mediums in mural painting to make the execution more flexible, and to make use of a wider range of pigments. In this sense, pure buon fresco, while not exactly a utopian ideal, is particularly rare due to its complexity and the exceptionally high demands it places on the artist’s skill.
Although some frescoes that incorporate combined techniques, such as those by Piero della Francesca and Giotto, have remained in relatively good condition thanks to a strong underpainting on fresh plaster, today we can confirm that works executed by masters of buon fresco, such as Ghirlandaio, Fra Angelico, Michelangelo, Raphael and Vasari are preserved with exceptional stability. In contrast, paintings that relied heavily or entirely on a secco methods, most famously Leonardo da Vinci’s Last Supper, have suffered far greater deterioration due to the limited lifetime of these materials on a wall.
