On 17 October 1786, Goethe arrived in Cento, ‘a friendly, attractive little town’ halfway between Bologna and Ferrara on the Via Emilia. As so often, the countryside delighted him. He admired the ‘sea of poplars’, the ‘rich soils’, and the mountains looming grandly in the distance. But what really piqued his curiosity were the paintings by Giovanni Francesco Barberi (1591-1666), better known as ‘Guercino’. And no surprise. As Goethe explained:

Guercino is a profoundly good, wholesomely virile painter, without crudeness. Rather, his things have a delicate moral grace, a calm freedom and grandeur, and at the same time something unique… The lightness, purity, and perfection of his brushwork are astonishing. 

It is hard to disagree. More than 200 years later, Guercino still ranks as one of the most important – and unmistakable – artists of the Italian Baroque. Less sentimental than Guido Reni, yet more subtle than Poussin, he is as remarkable for his vivid colours and dramatic chiaroscuro as he is for his famous squint (‘Guercino’ is the diminutive of guercio, cross-eyed). And it is no coincidence that he is currently enjoying something of a renaissance. Over the past year, there have already been landmark exhibitions at Waddesdon Manor and the Pinacoteca Nazionale in Bologna; and there will be another at the Scudiere del Quirinale in Rome in a few weeks’ time.

All these exhibitions leave a crucial question hanging. What was the secret of Guercino’s success? This is what the latest exhibition at the Musei Reali in Turin sets out to answer. Comprising more than 100 works, from 30 galleries and collections around the world, it explores how Guercino learned ‘the painter’s trade’ (il mestiere del pittore): how he devised his style, how he managed his workshop, how – in short – he ran his business.

There was nothing in Guercino’s background to suggest that he was marked for greatness. Born into a family of peasant farmers, his horizons were never wide. His strabismus – reputedly caused by a shock while he was a baby – didn’t help, either. When he was barely six years old, however, he showed a remarkable aptitude for drawing; since his parents didn’t think he was much good for anything else, they allowed him to be apprenticed to a local artist – who, on recognising his ability, sent him to Bologna, then the epicentre of the Italian Baroque.

This undistinguished background was one of the major reasons for his success. Precisely because he came from nowhere, he knew that he would only earn decent money if he found a way of setting himself apart from others. He did this not by following a single style, but by absorbing as many contemporary trends as he could. Take a work like St Sebatian Tended by Irene (1619). Painted just as he was coming into his own, it’s a neat resumé of what he’d learned by that point. The first thing you notice is his debt to Caravaggio. St Sebastian is prostrate on the ground, as you’d expect. But while his face is cast in shadow, his limbs are picked on with startling flashes of light – as is the face of St Irene – brilliantly shifting the focus from the saint’s suffering to the care he is receiving. Then there’s the composition. This is pure Caracci. Guercino had met Ludovico Caracci (1555-1619) while studying in Bologna and had been deeply impressed by his insistence on the close study of nature. Returning to Cento in 1616, Guercino then founded the Accademia del nudo where anyone could learn to draw the human form from life. He even put out a book, the Manuale per i principianti del disegno (1619), an encyclopaedic collection of life studies. And you can see the fruits here. The elongated figure of St Sebastian, the downturned head of the doctor (an unusual inclusion), the expectant gaze of St Irene – are all given a vivid solidity, less monumental than in mannerist art, but infinitely more immediate. Finally, there’s the colouration. While the dominant tones, all brown and ochre, owe much to the Ferrara School, the brooding sky – echoing Irene’s skirt – is Venetian through and through.

This marriage of influences allowed Guercino to appeal to an unusually wide audience, though patrons didn’t just fall out of the sky. They had to be cultivated. And at this Guercino was a master. Each stage of his career – each step on the ladder to fame – was marked by an exceptionally close relationship with a different patron. By far the most important was Alessandro Ludovisi, the archbishop of Bologna. A noted connoisseur, he quickly recognised Guercino as a ‘great draftsman and a most felicitous colourist’ – and immediately became one of his chief patrons. Guercino knew what Ludovisi liked. Between 1617 and 1618 he painted a group of four paintings for Ludovisi and his nephew (The Return of the Prodigal Son, Lot and His Daughters, Suzanna and the Elders, St Peter Raising Tabitha). Reunited here for the first time in almost 400 years, they are charged with daring contrasts: chastity and desire, love and incest, death and resurrection, sin and salvation. No surprise that, when Ludovisi was elected Pope Gregory XV in 1621, he took Guercino with him to Rome and showered him with further commissions. Sadly, only a handful of these have made it into the exhibition, but you get an impression of just how high Guercino rose from Pietro Francesco Garola’s Interior of St Peter’s Basilica in Rome (c.1710), in the corner of which, you can catch a glimpse of Guercino’s immense Burial and Glory of St Petronilla (1623).

The intensity of Guercino’s relationship with his patrons shines through into his portraits. Some of these are extraordinarily intimate, none more so than the Double Portrait with Guercino and Giovanni Battista Manzini (1660-4). At the time, Manzini was a distinguished aristocrat, at the peak of his fame as a man of letters. He knew it, too. On his chest, he wears the order of Ss Maurice and Lazarus, and a satisfied smile plays on his lips. What’s surprising is that he asked Guercino to include himself in the portrait, too. This was a sign not just of social equality, but also of genuine affection. And Guercino replied with faultless charm. Receding into the shadows, he is depicted with his pallet and brushes in one hand, and the other resting on the easel where Manzini’s portrait is standing. It’s as if he is asking Manzini what he thinks.

Patronage was only part of the story, though. It was all very well having an appealing style and plenty of orders, but if you couldn’t churn paintings out efficiently, you were going to come unstuck. And it is fascinating to see how effectively Guercino organised his workshop to capitalise on the opportunities which came his way. One of his tricks was to divide the labour up. He recruited his brother, Paolo Antonio – and together they collaborated on a number of works. While Guercino tended to tackle the figures, or even just the faces, Paolo Antonio excelled at painting fruits, vegetables, animals, and household objects. The wonderfully succulent mushrooms, figs, grapes, and plums in The Greengrocer (1655) are all his work, for example.

Another trick was to recycle compositions and models. Once Guercino found that a particular pose worked, he would reuse it, sometimes several times over. Take St Matthew and the Angel (1622) and the Liberation of St Peter (1622). The lighting may be different, but the main characters have almost exactly the same pose. Each one lies on his left side, propped up on an elbow, his right hand resting on the floor or a book, while turning to look at an angel, appearing over his right shoulder.

Perhaps his most effective secret was copying. During the 17th century the art market was extremely competitive. Works by celebrated artists – like Guercino – were in high demand. Patrons often vied to buy the best works; and if they didn’t win, they could either arrange for another painter to make a copy or hold a grudge against the artist for favouring his rival. Either way, the artist risked losing money. Guercino realised that he could avoid this by making copies of his best works. Take Lot and His Daughters (1650; Dresden, Gemäldegalerie). Two years earlier, a certain Girolamo Panessi had bought the Samaritan Woman at the Well (1658) for 113 scudi – and he was now anxious to buy Lot and His Daughters. Unfortunately, Guercino had already sold it to Manzini by then. He didn’t want to disappoint Panessi, either, so when Manzini decided to give the painting to the Duke of Modena, Guercino seized the opportunity to take a look and make a copy (Paris: Louvre). Everyone was happy; and Guercino made money twice over.

As this suggests, Guercino was a shrewd businessman. One of the most interesting parts of this exhibition deals with his libro di conti (account book). Recording thousands of transactions, this shows that he was extremely attentive to everything he spent. He was even more careful about his earnings. He was shrewd at negotiating prices for his works. Partly because he was able to divide the labour, reproduce compositions, and copy certain works, he had a very clear sense of how much a particular painting should cost – even developing a sort of pricing structure. While the St Francis Receiving the Stigmata (1633) brought in only 100 ducats, Ss Gertrude and Lucrezia (1645) – showing two full-length saints and two putti – earned him 260 ducats. He was keenly sensitive to the market, too. When the people of Cento were no longer able to pay enough, he took himself off to Bologna, where he could command prices commensurate with his growing fame.

This is not to say the exhibition is flawless. By far the weakest section is devoted to ‘science vs. magic’. It is, of course, true that Guercino had close ties to the world of science. Through his patrons in Bologna and Rome, he met two of Galileo’s closest friends, Giovanni Ciampoli and Cesare Marsili; and his fascination with their astronomical research can be glimpsed in works such as Atlas (1646). Yet it is quite wrong for the curators to imply that science and magic were mutually exclusive. They weren’t. As Anthony Grafton has recently pointed out, they were parts of ‘the same rich tapestry’. Each was seen as a means of gaining access to knowledge about nature. Don’t forget that even Isaac Newton was obsessed with alchemy. So it is somewhat annoying to see Guercino’s Astati, the Mage Brumio (c.1618-20) condescendingly treated as a sort of aberration.

Also rather tiresome is the section on ‘sibyls and strong women’. Other than to tick a box, it is difficult to see why this has been included. Most of the subjects treated by Guercino – e.g. Lucrezia, Cleopatra – were already extremely popular, so singling them out as evidence of commercial acumen is hardly convincing. This is a real pity, as many of the pieces are fascinating in their own right and deserve much closer attention. The Death of Cleopatra (1648), for example, seems to anticipate Manet’s Olympia; while Diana (1646) – crowned with a crescent moon – is both rich in unusual iconography, and faintly evocative of Magritte. It is a pity they are displayed to so little effect.

These flaws do little to detract from the overall quality of the exhibition. Rarely has ‘the painter’s trade’ been treated so thoroughly – or to so much effect. It adds a completely new, and utterly fascinating, dimension to Guercino’s oeuvre. So much so, in fact, that, by the end, his business acumen almost seems more impressive than his artistic genius. And if that isn’t worth the price of a ticket, I don’t know what is.

Guercino: The painter’s profession is at the Musei Reali Torino until 15 September.