When you visit Italy, you see a lot of frescoes, a technique of wall painting. Have you ever wondered how they were made, and why they still look so good? This article details how frescoes were painted in the Renaissance.

Fra Angelico, Annunciation, Convent of San Marco, Florence / Wikipedia

The rise of fresco in Renaissance Italy

Fresco technique was used in the Ancient world and is generally accepted as being the main technique for wall decoration in ancient Roman art. There are well-preserved examples of Roman frescoes in Pompeii and the Bay of Naples. In the Middle Ages, fresco was still a wall painting technique, though important, expensive decorations were preferably made in glass mosaic tesserae – think of Venice’s San Marco or the churches of Ravenna. In the period we call Proto-Renaissance, around 1300 in Florence and connected to the artist Giotto, fresco came back into favour for a few reasons. It was the best form of painting for monumental architecture, much of which was being built at this time – in Florence, they were building the major churches Santa Croce, the Duomo, and soon after Santa Maria Novella. Fresco could be done quickly and quite cheaply compared to say, sculptural decoration, it could cover vast surfaces, and it is relatively permanent.

How fresco is made

A fresco workshop in Florence

Fresco (or affresco) means wet in Italian. In a real fresco painting, paint is applied to wet plaster. Thus it is incorrect to use the term “fresco” for just any “wall painting”, as it should only define paintings done with the fresco technique, on wet plaster. Wall paintings done on dry plaster is called a secco (meaning “dry” in Italian); sometimes, details such as a face or decorative trim on textiles may be applied a secco on top of a fresco, making for loss of detail over time, because dry painted areas don’t last as long. In fact, frescoes are almost permanent because of their chemical composition:

1) The active ingredient in fresco is LIME PASTE, which is produced by heating CALCIUM CARBONATE with limestone.
2) LIME PASTE + AIR changes back into calcium carbonate, hard crust (carbonatation). If pigment is applied to this mixture when wet, it becomes trapped into the wall and is fairly permanent because it is very chemically stable.

How to paint a fresco

Two of the Nine Worthies and Nine Heroines, Godfrey of Bouillon and Delfile. Fresco, circa 1416-17. Photo: Chris Dobson.

A man named Cennino Cennini an artists handbook around 1400, The Craftsman’s Handbook or “Il Libro dell’Arte”. He describes exactly how frescoes were made at his time, which I sum up here.

STEP 1: scaffolding

In small space like chapels, scaffolding is built across space, with wooden poles stuck into the walls. These parts are then filled in with plaster and may be painted over a secco. If you notice square holes in the wall, chances are this is where the scaffolding originally was inserted.

STEP 2: prepare the wall

You’re going to apply plaster to the wall and you want it to stick, so you rough up the surface with a small pick-axe.

STEP 3: arriccio

Arriccio is a layer of rough plaster made of a mixture of lime paste and large granules of sand. You smear it onto the wall and let that dry overnight.

STEP 4: map out the drawing

The 14th-century artist would sketch out the major outlines of his painting with a reddish-brown paint directly onto the arriccio. This part is called the sinopia, an underlayer of the fresco that can sometimes be uncovered through restoration – you may see this sinopia displayed in museums. Sometimes you may actually see sinopia on walls where the top layer of the fresco has been ruined. This preparatory drawing in sinopia is a handy guide for the artist and also a way to show patron what he’ll be getting.

Later in the 15th century, the practise of direct sinopia painting was used less often. As drawing became more important in the practise of the visual arts, many artists made a series of preparatory designs culminating in a cartoon, a life-size drawing on paper. They pricked the cartoon with a needle and held it up to the arriccio; this page was then “pounced” with a sack of carbon so that a black outline was made. Since this drawing is then covered up with the intonaco (see below), it must have been hard to keep the drawing in mind. For this reason, sometimes the drawing was also held up to the last layer of plaster and it was scored with a tool. That’s why sometimes you can see a depression or outline around some of the larger shapes in a fresco, like outlining a major figure.

STEP 5: intonaco

The day to paint has arrived. Obviously it’s not all done at once – each day’s work is called a giornata (which is simply the word for “day” in Italian). This corresponds to a plaster patch that is the amount of work the artist could do in one day. You prepare your intonaco plaster with the same lime and sand as the first layer, but the sand is a finer grain and there is more lime. This mixture is then spread onto the space you intend to work on that day. Interestingly, this covers up the underpainting (or charcoal outline), which the artist had to keep in his mind! If you look closely, sometimes you can see the giornata divisions in a fresco; these were applied judiciously to try to hide the lines but are usually around major shapes.

STEP 6: paint

The paint (which is simply pigments) is applied directly to the plaster while it is wet, which is only a 2-4 hour window of opportunity, after which the plaster starts to dry and it gets very difficult to paint. You work from the top down (because the paint drips!) and try to do large areas like sky all at once because it’s very difficult to match colours the next day. This process is very difficult because once you apply the paint, it’s there and you can’t make mistakes. In fact, paint layers are thin to transparent, so the pigment was added in layers. Colours could also be mixed by doing this.

Only certain types of colours are good for fresco painting. These are chemically stable earth pigments like terraverde, yellow ochre, red, white, charcoal black. Other pigments would react with air and discolour – for example, lead white turned black over time, azzurite blue turns green. There are some late Medieval / Early Renaissance fresco paintings from before they realized these problems; lead white pigment was used and now the frescoes look like photographic negatives, with black where the white was! An example of this is the Crucifixion by Cimabue in the Upper Church of San Francesco in Assisi.

Cimabue, Cruxifix, Upper Church of San Francesco Assisi / wikipedia

STEP 7: a secco

Finishing touches were applied a secco, or after the plaster had dried, and these tend to be less permanent and fall off with time. Sometimes the finest details in faces and other sections were done a secco. Gold leaf details were applied last, applied with fish glue. The very expensive blue pigment was often applied a secco, and to make it stand out, the fresco area underneath was done in red; over time, you may see a red sky that surely was not intentional, but that was originally blue. An example of this is the apparent “sunset” in the Crucifixion by Fra Angelico in the chapter house of the convent of San Marco. The background here was intended to be a blue sky that is gradually darker. Pure blue dry pigment was applied where you see the white area, and then in the upper area, red underpainting was used to make the blue be darker. Since much of this dry pigment fell off over time, the way we see this fresco now has changed. The figures are done in real fresco and have remained perfectly preserved.

Crucifixion with Saints, Fra Angelico, Chapter house of San Marco / WIkipedia

San Marco Museum: New Display for Beato Angelico Room

The preservation of frescoes

Because of their chemical composition, frescoes are permanent unless they are affected by damaging outside forces. The main one damaging factor is sulfur, which turns limestone and marble into dust. Sulfur attacks frescoes through air pollution and water. Water also damages frescoes, causes blistering and mold.

Of course, the ravages of time can also be damaging. Sometimes, the fashions of later centuries meant that often perfectly good frescoes that we would admire today were overpainted or simply white-washed! Vasari did this to Giotto’s frescoes in Santa Croce, which is why they are not in great condition now. Bombings, in Italy mostly from WWII, caused serious damage in other areas, as did the Florence flood of 1966.

Modern painting restoration can clean as well as “consolidate” frescoes, ensuring their legibility for years to come.

Get to know Gaddi up close at Santa Croce


Fresco requires great skill and speed. The process requires artists to plan ahead, to think of space as subdivided into sections, and to think of design in terms of strong shapes. This leads to a new appreciation, especially in early Renaissance Florence, of the monumental, of powerful and large forms.

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