It was an orgy. The Paris sale of the Portalis-Gorgier’s art collection took place in the spring of 1865, and the plutocrats of Europe came to town. Chief among them were Lord Hertford and Baron de Rothschild, who had a habit of writing their bidding agents blank cheques: no price would be too high to secure the object they wanted. When the two squared off over a painting by a newly fashionable Dutch master, the scene was set for mutually assured demuneration.

A French art journal reported on the fallout in its next edition: ‘the Portrait of a military man, by Franz [sic] Hals, 51,000 francs – fifty-one thousand francs! to Lord Hertford, against M. Rothschild, who had given his agent unlimited funds – very embarrassing!’ This ‘military man’ picked up a new nickname when he arrived in England: ‘the laughing cavalier.’

No portrait by Frans Hals had ever sold for more than a few thousand francs. From now on, they would never sell for less. The defeated Baron licked his wounds by buying another Hals two months later for a crisp 35,000 francs.

Few artists have had a more spirited afterlife than the seventeenth-century Dutch painter Frans Hals, but the facts of his biography are sparse. He worked his whole life as a painter of individual and group portraits in the wealthy Dutch town of Harleem, and the dates of his activity, 1610-1666, roughly bookend the golden age of Dutch painting. In his lifetime his work was prized by the merchant collectors and fellow artists alike; after his death, his fame dissipated until the Cavalier made headlines three hundred years later.

The man in the painting is neither laughing, nor a cavalier, but an unknown wealthy gentleman in fabulous clothes. His engrossing and ambivalent expression crystallises into attitudes of vanity, watchfulness, humour, reserve, intelligence, ignorance and contempt depending, quite literally, on the angle you view him from. He is the most prized likeness in London’s Wallace Collection, and the centrepiece of ‘Frans Hals: the Male Portrait,’ which is currently showing in the Wallace basement.

The cavalier brought Hals back into the light. His broad, wild brushstrokes endeared him to the Impressionists, as did his understated mastery of colour. Walking from one end of the exhibition to the other one can see how his technique grew more free as time went on; the last portraits are so wild that certain passages feel almost expressionist. His palate changes too, becoming both narrower and more finely differentiated. ‘Hals’, Van Gogh wrote to a friend, ‘must have had 27 blacks.’ The art critic Theophile Thoré declared simply, ‘Franz Hals, c’est un moderne’.

Reputations change. Before Hals was modern, he was a dishevelled Haarlem drunk with ham-thighs and rosy cheeks, who neglected his work to frequent the local taverns. ‘It was Franz’s custom to fill himself to the gills each evening,’ wrote Arnold Houbraken in an extremely inventive biography written decades after Hals’ death.

It’s not clear whether Hals’ reputation as an incorrigible lush was prompted by his free technique, but the idea stuck around for a long time. Joshua Reynolds, praising his ability to snag a man’s quintessence in paint, chastised him for his unfinished-seeming surfaces. ‘Frank Hals,’ he lamented, lacked ‘patience in finishing what he had so correctly planned.’

Reading the literature on Hals one sometimes feels there are more myths to bust than there are facts to relate. It’s one of the curiosities of his life that someone so renowned for his ability to capture the personalities of his sitters should have left so little record of his own.

This is the hard stuff that the archive will yield: his family were merchants who came to Haarlem from Antwerp, in Flanders. He appears in 1610 as a master in the Haarlem painter’s guild: an advanced position, given he wasn’t yet 30. He married shortly after, but his wife and two of their three children were dead by 1616. The historical record tells us nothing of how Hals felt about this sudden fluorescence of catastrophe.

At this time, Hals was also member of the St. George civic guard – more of a dining club than a real fighting force – and that year he painted a group portrait of them for his first major commission. This painting, the scholar Seymour Slive once said, ‘announces the golden age of Dutch painting like a cannon shot.’

In the winter of 1616 he travelled to Antwerp, which one could reasonably claim as the epicentre of Northern European painting at this time. It would have been difficult, not to mention professionally neglectful of him, to miss the paintings being created there: immense Rubens altarpieces, as well as works by the young Jordaens and Van Dyck. He returned to Haarlem at the end of the year, and after that rarely left the city, painting constantly to support the eleven children he had by his second wife.

Haarlem was the right place for Hals. Individual cities in seventeenth-century Holland had distinct artistic preferences, and the ‘broad-brush’ style Hals developed would never have flourished in Utrecht or the Hague, where a more courtly kind of portraiture was preferred.

The charismatic, free orchestration of Hals’ brushwork is now on display at The Wallace, where a host of important male portraits have been assembled. They seem to cry out for anachronism: a jagged black and white sleeve feels like a detail from Pollock; the deep, textured blacks of the velvet doublets recall Manet and Rothko. Castiglione’s ideal courtier aspires to live with sprezzatura – a nonchalance that conceals all art and effort. Hals’ paintings are one step beyond this: they perform brilliance achieved with the bare minimum of care.

This isn’t impressionism either, though an ear might be assembled loosely from a few splotches and a sleeve rendered with a blur of blacks and greys. Standing in front of them you see that this roughness opened up possibilities for Hals that go beyond optics. In the portrait of Pieter Van der Broeke one can hear the rustle and scrunch of his dark robe; an inch away from the canvas one sees white paint daubed on his chin, but at a distance of a few feet the mark resolves into the dynamic modelling of the sitter’s jaw. That Hals’ paintings have a reverse vanishing point – a distance at which the brushstroke suddenly hides itself in the whole – is recorded by a contemporary. Hals portraits’, the poet Cornelis de Bie remarked, lacked only ‘life itself’ when seen from a distance.

If you look left and right down the row of paintings, you’ll see people moving back and forward from the portraits, trying to catch the moment at which a series of marks instantiates itself as a likeness. As time goes on, it’s as though he is playing chicken with the limits of what the eye will accept. In the painting of Tieleman Roosterman, the eye initially admits the dark left shoulder as a robe, or a patch of shadow. It’s only after one really looks that the realisation dawns: fully half his body is a single plane of matte black. One can see this could become a sort of daring entertainment in and of itself, a local rage fed by titillated clients: how far will he go this time?

These paintings are instant, alive, utterly legible in a way that delights before it astonishes. You can tell at once who’s thick and who’s thoughtful, who’s strong and who’s weak, which man is rough and which one smooth. The composition process though, was careful and consistent – and it would have taken more time than half an hour in a tavern. Careful analysis of Hals’ paintings has shown that they were worked up over a five-step process: first an oil-based ground was applied to the canvas, followed by thin washes of underpaint, carefully blended. The canvas was then blocked in with shapes and lines. What we see today is mostly what came next, where the clothes and face were worked up.

The final touches would be the lips, the eyes and certain highlights: the long vertical stroke that models the light on Isaac Abraham Massa’s nose, for instance, which is the lightest white shade on his face. Sometimes the ground is actually visible as a mid-tone, as in the portrait of a man with a brush goatee and collar; one can see it through the folds of lace. This is the art that Hals concealed: the intelligence that knew to hold onto that first muddy tone so he could set the portrait off against it at a later stage.

We have had Hals the modern, Hals the drunk: how about Hals the magician? His portraits are at once performative and illusionistic, constantly pretending to expose their methods even as they hold onto their secrets. Each likeness teases the revelation of its sitter’s personality, but as in the case of the cavalier, our responses can change radically from moment to moment. This isn’t the deep, ‘true’ self, but the self as it’s performed: the pretence of mastery, the affectation of disdain, the attempt at seriousness.

In the exhibition’s final portrait, a haze and whirl of greys barely register as a man’s cloak, the pink and bloody splotches just about converge into a sickly countenance. It’s hardly surprising that we wonder who this man was. Personality, you think. Whoever painted this must have had a lot of it. Surely? But then the show is over, and the man himself is nowhere to be seen. ­

Frans Hals: The Male Portrait is at The Wallace Collection, London until 30 January 2022