Shunga: Sex and Pleasure in Japanese Art, British Museum, review Halfway through Kitagawa Utamaro's series of prints Poem of the Pillow, one of the most elegant and exquisitely refined works of erotica ever created, we are given a sudden view of coition seen from directly behind a pair of large, hairy and rather gnarled testicles. But that is the essence of shunga, the popular erotic prints produced in Japan in the 18th and 19th centuries: on the one hand superbly rendered contrasts of colour, texture and pattern, on the other genital conjoining that leaves absolutely nothing to the imagination. While these images were well known to artists during the 19th-century vogue for Japanese prints - Toulouse Lautrec, Beardsley and Picasso all owned sets - they tended to be kept hidden in drawers. The first British exhibition of shunga took place at the V&A in 1973, since when some of the less explicit images have become popular as greetings cards. But this is the first exhibition to set the genre in its historical context, to ask what function these images served, whose pleasure we are supposed to be watching, and why the sexual organs are always so preposterously over-sized. The first images here are hand-painted scrolls, predating wood-block printing, and the preoccupation with the grossly enlarged male member is established in a hilariously exuberant brush drawing of a penis-measuring competition from 1600. According to a quote from an artist recorded in 1254, it has less to do with physiological reality than a collective propensity for aspirational fancy: "if "the thing" were depicted in its actual size there would be nothing of interest, for that reason don't we say that art is fantasy?" The earliest wood-block prints from the early 17th century are pretty crude in their execution, but shunga had got into its stride a century later, and once the conventions were established it was a question of refining them within relatively narrow limits. While there are occasional naked scenes, the way the eye is led over contrasts of sumptuously patterned clothing and pure white flesh towards glimpses of heavily veined penises and delicately drawn, oyster-like vulvas is essential to the shunga experience. Deciphering the physiologically improbable postures draws us in and delays pleasure, while the similarity between the swooning features of the women and the smooth-faced girlish men adds a further disconcerting frisson to the masterpieces by Shuncho, Hokusai and their peers seen in this exhibition. While we think of erotica as an essentially solitary pleasure, these prints - invariably published in sets of 12 or in books - were a communal phenomenon shared by married couples and groups of friends, handed down as heirlooms and passed to young women, essentially as sex manuals. There's a lot of bawdy humour here. We see a grand lady being serviced by her masseur, a cat toying playfully with a man's testicles and a cloth merchant being pounced on by six randy housewives. Shunga reached its apogee in 1788 with Utamaro's Poem of the Pillow. These are images that immerse you in the world of the bed, expertly balancing languor and ecstatic urgency. Yet the best of them are perhaps the least explicit, teasing and inferring rather than rubbing your face in it. But then they are interspersed with images such as the one described at the beginning of this article, together with a disturbing scene of rape and - most grotesque of all - a pair of Europeans hard at it. There's all of sexual life here (or certainly most of it) in just 12 images. Oct 3-Jan 5. Tickets: 020 7323 8181; britishmuseum.org