Following on from my long series about the different media used in painting, I thought it might be interesting to examine some paintings to see how those media have been used to create works of art. In this first article, I look at one of the greatest fresco paintings of all time, Masaccio’s Holy Trinity, in the Basilica of Santa Maria Novella, in Florence, Italy.

Masaccio was only twenty-six at the time that he completed this six metre (21 feet) high fresco in 1428. It is so startling in its use of perspective projection that, when viewed from the right place, it works as a trompe l’oeil. Yet accurate linear perspective projection had only been invented a few years earlier.

As was usual at the time, this was commissioned by ‘donors’ or patrons probably from the Berti family: the man dressed in red, kneeling in prayer at the left, and his wife at the right.

The finished painting shows the traditional Christian Trinity of God the Father (top), God the Son or Christ (on the crucifix), and God the Holy Spirit (white dove flying from God the Father). At the foot of the crucifix are the Virgin Mary (left) and Saint John the Evangelist. The tomb at the bottom of the painting is that of Adam, the first man. The inscription on that tomb reads Io fui gia quel che voi siete e quel ch’io sono voi anco sarete: ‘I once was what now you are and what I am, you shall yet be’.

For all his youth, Masaccio was a very experienced and successful fresco painter by this time, and had completed a series of superb paintings in the Brancacci Chapel, for example. He was mastering the use of linear perspective projection, and must have made the decision to make this work a showpiece for the new technique.

The two principle sources of information about perspective in Florence in the period 1425-1435 were Filippo Brunelleschi himself, its ‘inventor’, and Leon Battista Alberti, who was in exile in Genoa and wasn’t allowed back into Florence until 1428. It was Alberti’s later book which was to provide the geometric foundation for most linear perspective in the Renaissance.

Donatello, the sculptor, was a close friend of Brunelleschi and might have been able to work with Masaccio on perspective. However, he was probably away most of the time working on commissions in Pisa and Siena. It’s therefore most likely that Masaccio worked with Brunelleschi on the drawings, to ensure that it was projected correctly.

In addition to the geometric composition, Masaccio would have completed a final study which was used as the basis for other details. This is traditionally squared up to facilitate scaling up to full size, as has already been done in Gustave Moreau’s pen and ink drawing above.

He would also have made a preliminary plan for the painting. Because buon fresco is painted into fresh, wet plaster, the artist can only plaster and paint a certain area each day – known in Italian as the giornata, a day’s work. Before starting to paint, Masaccio should have evolved a plan of the painting campaign, which starts at the top and works downwards.

Once ready to start the painting, a team of carpenters will have erected wooden scaffolding to give Masaccio and his assistants access to the whole of that section of the wall, to the full height of over six metres (21 feet). Masaccio is likely to have taken considerable interest in this: he was going to be working at sufficient height that any failure of the scaffolding would be likely to result in his serious injury or death. A surprising number of fresco painters did indeed fall from or with scaffolding and suffer the consequences.

The first stage would have been completed by assistants, who laid a rough underlayer of plaster known as the arriccio over the whole wall, and left it to dry for several days. This layer often contains abrasive sand particles to provide a key for the final layer of plaster.

Once that had dried completely, Masaccio and his assistants transferred the drawings onto the surface of the arriccio. This may have been performed by scaling up from the squared drawing and painting using a red pigment sinopia, or full-size drawings may have been pricked to make holes in the paper and a bag of soot banged against that paper when held against the wall – a technique known as pouncing. Masaccio is known to have used both techniques, and may well have used each in different sections of this work.

On each day of painting, assistants would prepare the colours by mixing pigments in water. That day’s supply of plaster, the intonaco (meaning plaster), is then prepared by mixing water with lime. That day’s giornata is covered with a thin layer of intonaco, and about an hour later Masaccio started painting into it. He then had about eight hours before the intonaco dried and he could apply no more fresh paint.

Like many of the best fresco painters, Masaccio extended his painting time by using paint mixed with milk or casein and a little lime – effectively a lime-based casein paint – which could be laid onto dry intonaco.

The geometric requirements of this painting also merited special measures. When the intonaco was first applied, it was marked to indicate key construction lines, such as those in the barrel-vaulted ceiling, and down the pillars at the side. The remains of these incised lines are still visible when the fresco is viewed in raking light. In this case, there is evidence that Masaccio used lengths of string attached to a nail sunk at the vanishing point of the linear projection, below the base of the cross.

Giornate can sometimes become obvious over time, as shown in Giotto’s fresco in the Scrovegni Chapel in Padua, Italy.

During the conservation work and movement of Masaccio’s painting in the 1950s, the opportunity was taken to study its construction. Leonetto Tintori drew up a plan of all the identified construction lines and edges of giornate; I have sketched in the latter from a reproduction of a drawing made at that time, which has since been destroyed.

It’s estimated that the whole painting would have required some 24 giornate, although because of the long history of damage and attempts at its restoration, that number must remain flexible. Assuming that Masaccio painted six days a week, that would have required a minimum of four weeks working for at least ten hours each day. Fresco painting doesn’t permit easy alterations: if any repainting was required and couldn’t be accomplished using dry technique, that day’s giornata would have to be removed, replaced and repainted.

Masaccio’s linear perspective projection was implemented very well, accounting for the painting’s breathtaking three-dimensional effect. But within a few months of its completion, Masaccio was dead.

Extraordinarily, this magnificent work was covered over during renovations made by Vasari (the early biographer of artists, of all people) in about 1570. For nearly three centuries, it remained forgotten and invisible, then in 1860 it was rediscovered and moved (an extremely dangerous procedure for frescoes) to another wall in the church, leaving the tomb at its foot in place. When that tomb was rediscovered in the twentieth century, the rest of the painting was moved back to be reunited with its foot, and conservation work completed in 1954.

Additional details are given in this superb movie produced by the National Gallery of Art, Washington, DC.