Diego Rivera and Frida Kahlo: Portraits of a very modern marriage

If ever there was a glamour arts couple it was Diego Rivera and his wife, Frida Kahlo.

He was the master muralist who gave shape and colour to the Mexican revolution and its socialist future; she was the woman who developed an art of introspection and female sensibility all of her own, the lover of Trotsky and the embracer of sex in art.

Little wonder that Frida has been taken up by the feminist movement as an embodiment of independent female talent and ambition. Little wonder, too, that it is her art, personal, autobiographical and frank, which has risen in critical estimation while his, public, political and grandiose, has tended to suffer in comparison.

It wasn't like this at the beginning. A student of 21, she met him in 1928 while he painted murals in a ministry, pursued him and took him from his wife. Twenty years older than his new love, he was the artistic genius of the country, admired abroad as much as at home for his giant murals in public spaces. But, encouraged by him, she developed a style all of her own in painting and, taking his example, enjoyed an open marriage, with a succession of lovers of her own.

This is what makes her so attractive to feminist critics, as an independent spirit with a huge talent all of her own. But if you can take Frida out of her marriage, it doesn't mean that you can take her relationship with her husband out of her life or out of her art , which is the point of the joint show at the Pallant House Gallery in Chichester.

Good for the Pallant. Even before the show opened this month it came under fire for daring to display the two together, as if this deliberately diminished the female against the male, implying that Frida only existed as the spouse of her more famous husband. This is just perverse and, in its way, robs Frida of her individuality in order to make her an icon of modern sensibility. Rivera was immensely important to her, the most important influence, along with her father, on her life. It was he who encouraged her, who urged her to paint her experience after the loss of her first child (as later ones) and continued to promote her talent until her death in 1954. She ribbed him, she despaired of him, she had numerous affairs but never did she do other than admire him as an artistic giant of his nation and time.

Just look at her self portrait of 1943, "Self portrait as Tehuana or Diego in My Thoughts". It is a glorious painting of Frida in formal lace headgear. But it is also deeply symbolic. Diego's portrait appears on her forehead, her face (as in so many self portraits) is commanding but full of love, out of her head come threads in all directions. Look to the adjoining wall at her portrait of him in 1937, eight years after their marriage – a head and shoulders full of physical attraction as well as masculine presence.

The intimacy of relationships is dangerous territory for any outsider, and modern biographers are a little too eager to attempt it. We don't know what went on in the Rivera bedroom, whether the two were pained by their affairs and whether and how their relationship altered over time. The art has to stand on its own. But what is true is that Frida and Diego had a profound admiration for each other's work and, because their subject matter was so different, they were able to develop in their own way.

It's what makes a joint show so intriguing. The works are taken from the collection of Jacques and Natasha Gelman, the finest private holding of Mexican art in the world, which includes paintings and drawings by Frida and Diego in equal measure. They are all relatively small, which deprives Diego of the majesty of his great murals. But, even given that, they provide a surprisingly rich survey of the two artists.

Diego, who had lived in Paris and visited Italy and was more cosmopolitan than his wife, is represented by one of the striking symbolist landscapes he painted for his first New York show, in 1931, in which a female cactus is partnered by two male ones. A reference to her lover and husband? Whatever, it is a powerfully composed work. There is also the dramatically sensual "Calla Lily Vendors", a detail from one his murals, petals and stamens balanced by statuesque figures of two kneeling vendors, seen from behind. Lithographs of nudes remind you what a good graphic artist he was.

Frida, in contrast, is all personal and autobiographical. The painting she did in 1937 after the death of her child, "Self Portrait with Bed or Me and My Doll", is an almost unbearably painful, direct depiction of herself with a naked doll that represents her loss, eyes staring out with a gaze that is both blank and confronting. That same direct, commanding look is seen in all of her self-portraits, the dark eyebrows meeting over the nose, the lips full and slightly pouting, the dress very often in local Indian style to assert her Mexicanness and the moustache fuzz clearly visible above her mouth. They are not romantic images but they are self-examining, the pictures of a woman looking directly at herself in the mirror and examining her dreams as much as her life.

This is not a show to draw direct comparisons between the artists, although they share a deep sense of patriotism, a sculptural composition that harks back to Aztec reliefs and a use of luscious greens, stark whites and deep purples. And there are in this exhibition two portraits they were commissioned to do (among many) of Natasha Gelman. Diego offers a startling combination of the salon, the sitter draped across a settee as a society beauty, with the sensual, in an array of drooping lilies behind her. Frida's portrait, from the same year, is also of a society woman, with fur collar, silver earrings and curled hair. But the face is a mask and the eyes reveal a degree of emptiness.

The show ends with quotations from the artists. In one, Diego declares of Frida's death in 1954 that "it was the most tragic day of my life. Too late now I realised that the most wonderful part of my life had been my love for Frida."

In the other, Frida says that "being the wife of Diego is the most marvellous things in the world... I let him play matrimony with other women. Diego is not anybody's husband and never will be, but he is a great comrade."

At the end of this three-room show – which also has a room of photographs by Manuel and Lola Alvarez Bravo and architectural shots taken by Frida's father, Guillermo – you feel that love and some of the pain behind it.

Frida Kahlo and Diego Rivera: Masterpieces from the Gelman Collection, Pallant House Gallery, Chichester (01243 774557) to 2 October