The National Gallery is playing host to a gathering of distinguished Dutch burghers. It doesn’t look, on the face of it, like a bundle of laughs. Dutch Portraits is dominated by dreary-looking worthies dressed in black costumes, their pale, solemn features framed by white ruffs. But nothing, this exhibition suggests, is ever simply black and white.

This show is about the Dutch Golden Age and, though the faces that look out at us may at first glance seem forbidding, they speak of a society in many ways like our own. The Dutch Republic in the 17th century was a new nation, shaped by its astonishing, entrepreneurial success. Monarchs and aristocrats may still have presided over the rest of Europe. But the Netherlands was creating another sort of elite. In one generation, a merchant could make his fortune. He could become a man of rank. Surely we can relate to such democratic principles. These people share the same dreams, the same ambitions and possibilities as us.

The emerging middle classes were, quite naturally, keen to celebrate their newfound prosperity. And so portraiture flourished. Dutch Portraits, as its subtitle hastily reassures us, is about “The Age of Rembrandt and Frans Hals”. It is about the work of the finest painters of their era, and, in the case of the former, of one of the greatest artists who has ever lived. This show stirs a rich selection of Rembrandt’s paintings (including such superlative loans as The Anatomy Lesson from the Mauritshuis in The Hague) and several fine pieces by Frans Hals into a mix that includes some of the best and most representative images of an era in which, quite literally, hundreds of thousands of portraits were commissioned.

Pictures were ordered to commemorate important moments in people’s lives. They shared something of the function of modern-day photographs: recording betrothals and marriages, the birth of a child or a moment of professional success. Portrait painters were prepared to experiment, seeking out fresh approaches and compositions to please their clients. A collection of images that might at first appear rather uniform on closer inspection betrays an unprecedented diversity and imaginative depth.

The stiff formality of the show’s first pictures, painted at the dawn of the Golden Age, very quickly loosens. Paint is set free and poses relax as portraiture discovers a new freshness and starts to enjoy the adventure. When the Harlem merchant Willem van Heythuysen first commissioned Hals to portray him in about 1625, he had himself presented in traditional Renaissance pose, hand on hip, full-length and life-sized, gazing confidently down from his towering vantage point.

But ten years later, when Hals paints him again, the stately elegance of the polished public portrait has given way to the casual nonchalance of an intimate, small-scale portrayal. The spectator steps into a private room to find the sitter, still in his riding clothes, leaning back crosslegged in a chair that tilts as he swivels to look. Where earlier portraits are executed with an almost visible patience, the brush starts to skip more lightly about the canvas, capturing not just physical details but atmospheres and moods. Hals even brings a fleeting smile to the features of some his sitters. And his pair of plump newlyweds positively beam.

We see the people of the era in every aspect of their lives. Here are the grand portraits that boast status and wealth or the self-conscious dignity of high professional standing. But Charles I is presented by Gerrit van Honthorst in a moment of quiet privacy.

Artists experimented with composition. Rembrandt’s pioneering double portrait of Jan Rijcksen and his wife is wonderfully lively. The ship’s architect is disturbed at his studies by his wife, who, bustling in for a second, one hand still on the door handle, holds out a letter that has presumably just arrived. A fleeting moment is captured with grand effect.

Nicolaes Pickenoy presents the professionals of the Amsterdam surgeon’s guild in the middle of an osteology lesson. They are posed around a skeleton that happens, apparently, to be that of an executed English pirate.

The Countess of Nassau-Dietz chooses an extravagant mythological guise. She appears amid her children in the role of Charity with her plump white breast symbolically exposed. Meanwhile, the well-to-do housewife Ariana van Heusden, apparently keen not to scramble too far above her station, is depicted with her daughter going shopping at the fishmonger. Emanuel de Witte throws a piscine still life into the picture as part of the bargain.

Dutch painting at this period is characterised by an intense interest in the visual world. Every detail speaks, either in the language of symbolism (the hawk for the boy of high status, for example, the peach for the girl who is pure) or simply with the voice of authenticity (the lapdog that scrabbles in a Jan Mijtens portrait, for instance, leaves claw marks on the fabric of his mistress’s dress).

Slowly the visitor moves deeper into the world, decoding fashions and conventions. He starts to notice the different qualities of the lace, the degrees of extravagance of pairs of gloves, the newfound fashion for love locks or the way that, where well-to-do burghers boast ruddy complexions, those of nobler birth have far paler faces – except in the case of the poor man in the corner of the anatomy lesson, whose sickly pallor has more to do with a turning stomach.

Gradually the visitor gets to know the characters. Almost all the sitters are identified and the exhibition catalogue offers plentiful information. But even without reading it, you can start to relate to the people. You can sense the trembling watchfulness of the young wife as she poses, a shy creature inside the carapace of her grand new married woman’s gown, and smile at the tenderly uxorious husband who takes the hand of his wife in their rosy bower.

You can be moved by Willem van den Kerckhoven’s care for the wife and ten children, whom he groups around him in a charming pastoral assemblage. The souls of the babies that were lost to the family hover above them as cherubs. Who could resist leaning over to look at Salomon de Bray’s extremely rare baptismal portrait of a pair of tiny twins tucked into their Baroque cradle, two peas in a pod.

It doesn’t even matter if nothing is known of the sitter. Rembrandt’s 1667 Portrait of an Elderly Man, slumped in a chair, flushed with drink and rather ill kempt, is one of the most strikingly evocative portraits in this show. You can almost see him blinking away his bleary double vision, hear him suppressing a belch as he grips the chair handles for balance.

In the end, perhaps it is precisely because so many sitters at first glance look much the same, that we turn so attentively to their faces; searching out a sense of their individuality. The spectator who spends time will be rewarded. There is a moving authenticity to these portraits. These are people who want to represent themselves as they are, rather than as they should be. They want to celebrate the self of the self-made man.

For proof of this show’s complexity, just look at one of the costumes: see how many tones of black there can be in just one piece of cloth or notice how intricately the white ruffs and lacework are depicted. It is far from black and white. It is extremely subtle. For those with the patience to search, this will prove a wonderfully evocative and various show.

— Dutch Portraits: The Age of Rembrandt and Frans Hals is at the National Gallery, WC2 (020-7747 2885), from June 27

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