Delacroix exhibition: A major new exhibition shows how the painter was vital to Impressionism

Eugène Delacroix was wildly underappreciated in his own lifetime, but now is recognised for his supernatural voluptuousness

Delacroix's 'Lion Hunt' (Art Institute of Chicago)

No stranger to scathing reviews, Eugène Delacroix picked up some stinkers at his last Paris Salon in 1859. His Ovid Among the Scythians depicts the Roman poet banished to the Black Sea, watching the barbarous tribespeople. One is milking a mare: reputedly, the uncouth locals did that sort of thing. Loosely painted as a blur of temporarily arrested energy, the super-sized horse (unnaturally huge, critics carped) swings her mane in the wind, as much a part of this free-flowing landscape as the misty mountain-tops and scudding clouds. As for Ovid, and the brand of polite literary theme that the artist often chose as trigger or pretext: frankly, who cares? This is poetry in motion.

Ever since the essays of Charles Baudelaire, his most fervent champion, admirers have read Delacroix against the grain of his ostensible subject matter. The poet wrote that “a picture by Delacroix, hung at too great a distance for you to judge the harmony of its contours and the more or less dramatic quality of its theme, already fills you with a kind of supernatural voluptuousness”. Well, the 60-plus works selected for Delacroix and the Rise of Modern Art at the National Gallery – a third by the artist himself, the rest by diverse followers from Renoir to Matisse – allow us to get up close and personal.

Even at arm's length, though, they often bear out Baudelaire's contention that style – above all, colour – trumps content. For Baudelaire, “an analysis of the theme, when you draw closer, will neither add nor subtract anything from this initial pleasure… The limbs of a tortured martyr, the body of a swooning nymph, if they are skilfully drawn, connote a type of pleasure in which the theme plays no part”.

This kind of aestheticism, with formal virtues the alpha and omega of quality, has seeped so deeply into our ideas of art that it can come as a jolt to realise that earlier ages found it perverse, decadent, even immoral. The National's show – mounted in collaboration with the Minneapolis Institute of Art, which has lent a fabulous late Van Gogh of olive trees – chronicles the capture of Delacroix by an adoring crowd of Impressionists, Fauvists, Pointillists, even Abstractionists. They seized him from the academic critics who had first, in the 1820s, applauded the young prodigy's histrionic tableaux from Byron and the Bible, Shakespeare and Dante, but then turned away in outrage after sensational shockers such as (Byron-inspired) The Death of Sardanapalus in 1828.

In Impressionist eyes, Romantic storytelling brio counted for next to nothing in the art of the future. What mattered were the delirious vortices of colour and shape that whirl through paintings such as the Lion Hunt. Only a pedant or dullard fretted about theme. Far better – far more modern – to celebrate, as Baudelaire did in his obituary essay in 1863, Delacroix's ability “to evoke with colour alone what could be called the atmosphere of the human drama”.

These days, we routinely scoff at the Salon critics for their tut-tutting disgust at racy subjects or extreme technique. When the young Delacroix began to make an impact in the early 1820s, he did attract some establishment support. The French state bought his The Barque of Dante to the sort of commotion that, more recently, would greet the public purchase of a pile of bricks or a pickled shark.

Then, in 1828, came the debacle of The Death of Sardanapalus. At the National, we view not the full-scale original in the Louvre but Delacroix's later, smaller copy. Byron's pagan king expires among naked concubines and burly thugs in a head-spinning centrifuge of clashing colour and unshackled shapes. Oh dear, the strait-laced critics sighed. The painting was “a nightmare”, thought one. “The basic rules of art appear to have been rejected”, lamented another. All in all, “It is… unanimously agreed that the worst painting is M de Lacroix's 'Sardanapalus'”.

The sexual violence, sanguinary chaos and gruesome imagery of a royal demise struck conservatives, under the restored French monarchy of the 1820s, as both tasteless and subversive. We may sneer at their naivety. But art criticism in 19th-century Paris often had more in common with popular reviews of Hollywood blockbusters than with today's formalistic rituals. When moralising narratives still held sway, topic, tone and treatment mattered. The degradation of naked women and the bloody overthrow of civic order alarmed respectable critics much as some gory and misogynistic epic at the multiplex would now.

As an influence-and-inspiration job, the National's survey – the first large-scale outing for Delacroix in Britain since 1964 – buys into the familiar art-historical story of form and colour ousting narrative. That wonderful Van Gogh, for instance, came about because the artist had rejected the faith of his comrade-rival Gauguin that one could still – in 1889! – paint Bible personages in the Delacroix manner. So Van Gogh axes Jesus, but keeps the olive trees.

Cézanne, around the same time, said that “we all paint in Delacroix's language”. At the National, a River Landscape betrays his own debt. Yet you wonder how much the cult of Delacroix answered a need among Impressionists and their offshoots to find a noble ancestor from the grand tradition of Tiepolo and Rubens. This show also boasts a most untypical Cézanne, The Apotheosis of Delacroix, with the revered forefather flanked by artists of the 1890s like some Baroque saint. Christopher Riopelle of the National Gallery, co-curator of the exhibition, comments that “It's a wonderful statement about his allegiance and admiration for Delacroix – but at the same time, he's taking the mickey.”

Other disciples such as the proto-Pointillist Paul Signac elevated Delacroix into a semi- scientific theorist. This experimentalist contrasted primary colours with secondary shades in a self-devised technique he called “flochetage”. Look, though, at Signac's own painting of the Boulevard de Clichy under snow. It's a little gem of a Parisian scene, but a homage to Delacroix? Only up to a – rather technical – point. Signac's freeze-framed winter stillness stands at the end of very long street from the swirling, lurching dynamism of his mentor.

For all his painterly exoticism, however, Delacroix seems to have confined his passion to the palette. He lived chastely with his housekeeper and struck his many friends as a sober, upright gent – even a bit of a cold fish. Indeed, in his obituary piece, Baudelaire praises the late Anglophile artist (an admirer of Thomas Lawrence, John Constable and his friend Richard Parkes Bonington) for “his wholly English sense of loyalty, punctiliousness and dependability”.

Even when he made his famous expedition to Morocco and Algeria in 1832 and returned with a much-recycled sheaf of Orientalist scenes and figures, the “antique” look of north Africa and its invigorating light enthralled Delacroix more than the prospect of some Flaubert-style erotic spree. The Women of Algiers in their Apartment of 1834 – a painting that obsessed Picasso – comes over here as a cool, nuanced study in tints and textures, not some sultry harem adventure. Delacroix did not report but transmute. Details would fade away and he would paint the atmosphere, the aura: the impression, if you prefer. The visionary painter, Baudelaire affirmed, disdained minutiae but rather opened up “deep avenues for the imagination to wander down”. As Delacroix wrote in his journal, “To imagine a composition is to combine elements of objects that one knows… with others belonging to the interior, to the soul of the artist”.

As with Sardanapalus, the National shows the Women of Algiers not in its Louvre original but in a smaller version lent by the Montpellier museum. Van Gogh and Gauguin made a pilgrimage from Arles to see this one, which gives it a special value for an exhibition devoted to the artist's long-term legacy. But it also makes a virtue of necessity. Many major works by Delacroix never move out of France. Either they cannot budge (as with the heroic mural cycles in the Louvre, the National Assembly and the church of Saint-Sulpice), or else their iconic status nails them metaphorically to the walls. That goes for the revolutionary crowd-pleaser from 1830, Liberty Leading the People.

So the National must perforce present a more intimate, domestic, even downsized Delacroix. Who knew, for instance, that flower-painting meant so much to him – and to his acolytes? The floral room matches his own A Basket of Fruit in a Flower Garden – an almost-psychedelic starburst of blazing colour – with related works by Van Gogh, Courbet and Bazille. As Riopelle says, Delacroix's flower pieces revived a moribund genre. “They simply revolutionised this type of painting, opening it up to the avant-garde.”

Besides, the artist himself had insisted that “The first merit of a painting is to be a feast for the eye”. The polemics of the Salon have faded into dust. Only scholars care much for the sources in literature, scripture or antiquity that began these wild rides. Few people bother with that laborious colour theory. With Delacroix, the “feast for the eye” alone endures. Go and see your fill.

'Delacroix and the Rise of Modern Art' continues in the Sainsbury Wing of the National Gallery, London, WC2 until 22 May (nationalgallery.org.uk)