When was the last time a soap ad gave you spiritual pleasure?

It’s sheer coincidence the Art Gallery of NSW is hosting Alphonse Mucha: Spirit of Art Nouveau while the National Gallery of Australia is showing Gauguin’s World: Tona Iho, Tona Ao. Mucha and Gauguin were friends in Paris during that period we call the belle epoque, but it would be difficult to imagine two more different artists. One thinks of Claude Levi-Strauss’ famous work of anthropology, The Raw and the Cooked. Gauguin (1848-1903) is as raw as a mango plucked from a tree, but Mucha (1860-1939) is the greatest cake decorator in the history of art.

As an aspiring artist in Paris, the young Czech was among those who gathered in Madame Charlotte’s Cremerie to eat cheaply and listen to Gauguin hold forth. They met again in 1893, when Gauguin had returned, penniless, from his first trip to Tahiti.

Mucha, who had begun to make money as an illustrator, invited the older artist to share his studio. Gauguin, never one to turn down a freebie, took up the invitation. Unlike many of Gauguin’s acquaintances, Mucha would remain a friend, even though he has been described as prudish, whereas Gauguin was notoriously uninhibited. Where Mucha was idealistic and patriotic, Gauguin was a cynic who saw his homeland as hopelessly corrupt. In the art they produced, there is no comparison between Mucha’s elegant, flowing designs and Gauguin’s “savage” paintings, carvings and woodblock prints.

It was, perhaps, this yawning aesthetic chasm that preserved the friendship – along with Mucha’s largesse. The AGNSW show includes photos of Gauguin in Mucha’s apartment, including one in which he appears to be playing the harmonium without his trousers.

By the time Gauguin expired in May 1903, in his wooden hut on the Marquesas, Mucha had become France’s leading exponent of art nouveau, and one of the most famous and successful living artists. When he visited the United States the following year, he was greeted as an international celebrity – “the greatest decorative artist in the world”.

Born in the Moravian town of Ivancice, Mucha had attended Munich Art Academy before arriving in Paris in 1887. He remained devoted to careful drawing, showing no interest in the techniques of the impressionists or their scenes of everyday life. Art nouveau, which took its name from a gallery run by entrepreneur Siegfried Bing, would become a global sensation at Paris’ Universal Exposition of 1900. As a strongly graphic art, it suited Mucha’s temperament and lent itself to mass reproduction.

More than most movements, art nouveau found expression in the applied arts – in furniture, jewellery, glass, ceramics, interior decoration and even architecture. Mucha, a prodigy of energy and versatility, would embrace many of these mediums, designing jewellery and a shop for Georges Fouquet, and decorating the Bosnia and Herzegovina pavilion at the 1900 Exposition.

One can put a date on Mucha’s entry into mass consciousness: January 1, 1895, when his poster for Sarah Bernhardt’s play, Gismonda, hit the streets of Paris. Bernhardt was the original megastar whose every move was written up in the press. An exhibition last year at the Petit Palais in Paris brought together a huge volume of material relating to the actor’s stellar career, with Mucha’s posters prominently featured.

Gismonda, with its clear lines and “Byzantine” ornamentation, was a sensation. Bernhardt was so impressed she offered Mucha a six-year contract to design all her theatre posters. He delivered the goods, creating equally memorable images for plays such as Medea, The Lady of the Camellias and Hamlet, all featured in the AGNSW show.

Had Mucha confined himself to the Bernhardt posters, his legacy would be less ambiguous. Instead, he became the first artist embraced, indeed idolised, by the world of commercial advertising.

Mucha was a decorative artist of genius, but his reputation will always be tied to the advertisements, packaging and wallpaper that made his fortune between 1895 and the early 1900s. Think of Mucha today and it’s those dazzling, languid girls with long, free-flowing hair that spring to mind. He used them to sell biscuits, bicycles, perfume, beer, brandy, soap, chocolate, and cigarette papers. It was a winning formula: depict some winsome siren with a come-hither glint in her eye wrapped around the nominated product. They were exemplars of that old advertising cliche “sex sells”.

Female consumers were invited to imagine themselves as young and attractive as the girl in the poster, if only they ate the right brand of biscuit. For the men, they might not be able to possess the maiden holding the bottle, but they could certainly buy the beer. It may sound crude, but these were the formative years of mass advertising, when the line between fine art and filthy commerce was but imperfectly drawn.

It’s a line Mucha himself refused to acknowledge. The catalogue reproduces an amazing statement by the artist: “Posters were a good way of enlightening the wider public. They would stop and see the posters on their way to work, deriving spiritual pleasure from them. The streets became open-air art exhibitions.”

Pause for a moment and ask yourself – when was the last time you derived spiritual pleasure from an advertisement for soap or perfume? Not even the most brazen of bill posters would claim they were magnanimously creating an open-air art exhibition.

Some might believe Mucha was being as disingenuous as Jeff Koons, who claims his overgrown pieces of kitsch are all about “love”. One may groan at Koons, but we should never doubt the Czech’s sincerity. The catalogue is full of indications that Mucha held the highest aspirations for his glamour girls. He disliked the term “art nouveau” because he believed his work was essentially timeless. He saw his mission as an artist in broadly spiritual terms, often talking about “spreading light” or “enlightening” his audience. Eventually, he had to admit he had not found “true satisfaction” in the advertising posters, but the work that followed would be just as fixated on those beautiful, seductive nymphs.

Mucha saw the idealised female form as the ultimate vehicle for the messages he wished to send, whether it was a simple suggestion to buy a product or an allegorical evocation of the arts or the seasons. The problem for the viewer is to discriminate between the high and low registers. There are dozens of those trademark gorgeous creatures in this show, and they all tend to look the same. Instead of discerning a deepening spiritual profundity, viewers may find only a monotonous repetition. There’s something chaste and untouchable about Mucha’s flawless beauties, who have all the warmth of marble statues.

Think of Aubrey Beardsley’s decadent, ribald drawings as one extreme of art nouveau, and Mucha’s ice maidens as the other. If Beardsley was admired by a subculture, Mucha addressed the entire world. In 1904, on his triumphant first visit to America, he was already seeking a sponsor for his monumental project, the Slav Epic, in which he would depict the history of his people on 20 huge canvases. Having found a willing backer in Chicago businessman Charles Crane, he set to work with gusto.

The show features four of these canvases reproduced as wall-sized digital projections, tricked up with moving details such as falling leaves and wisps of smoke. There’s even a specially commissioned musical composition, although no one bothered to identify the composer.

A staggering amount of work would go into the Slav Epic, which was completed in 1928. One can only admire the skill and perseverance required to complete such gigantic history paintings featuring hundreds of individual figures. The glitch is that the sentimental, heartfelt patriotism behind the project feels dated and is mocked by the disastrous march of history that has followed. When we read how Mucha hoped that “through his art he might contribute towards the creation of a better world where people from diverse backgrounds might live in peace and harmony”, it poses a laugh-or-cry ultimatum.

When Czechoslovakia attained independence in 1918, Mucha designed stamps, banknotes and other public items, establishing a dominant national presence that few artists have ever matched. But the crowning glory, the Slav Epic, feels like a tragic anomaly, a 20-year masterwork of political kitsch.

As a contemporary equivalent, think of Jiawei Shen’s huge cycle of history paintings, documented in James Bradley’s Welcome to Babel, which won the documentary award at this year’s Sydney Film Festival. But where Mucha tells a histrionic tale of the hardships and glories of the Slavs, Shen documents the disaster of communism in the 20th century – not God’s own people, but “the God that failed”, to use Koestler and Crossman’s famous phrase.

Talk of people living in peace and harmony is characteristic of the catalogue for this show, authored by Tomoko Sato, curator of the Mucha Foundation in Prague. There is not a word of criticism for the saintly Mucha, whose career is presented as one long tale of triumph and despair. As usual, the AGNSW has taken a package, with virtually no original input, and added some dubious extras at the end – in this case, a Japanese vase and a suite of Ukiyo-e prints, along with a set of rock concert posters and album covers. It’s a poor attempt to underline the “relevance” of a show that is not relevant to Sydney in any special way. It’s tempting to believe the main reason we are celebrating Mucha is that this was a relatively inexpensive exhibition, offered on a plate and rumoured to have been turned down twice by another major Australian institution. Compared to Gauguin in Canberra or Pharaoh in Melbourne, it’s a piece of cake. Literally.

There’s no denying Mucha’s talent or achievements, but when one realises that variations on this exhibition have been touring the world for 20 years, it’s hardly the “landmark” that is being touted. All praise to the Mucha Foundation for doing their job so diligently, but a big question mark over the AGNSW, which is yet to justify a lavish new building chiefly notable for its large, empty spaces.

Alphonse Mucha: Spirit of Art Nouveau is at the Art Gallery of NSW until October 7.