The National Gallery used to have several remedies for new acquisitions that might prove morally controversial. One solution was to send pictures immediately on loan to Edinburgh, as the Scots were considered more lax. Garofalo's Allegory of Love (1530), with its two couples engaging in foreplay, was exiled from 1860 to the 1930s, and on return consigned to the basement until its restoration in 1992. More minor works, such as a copy of Michelangelo's Leda and the Swan, and Palma's Venus and Mars, both given in 1838, were hung in the director's smoke-filled office. But the most prevalent tactic was to "restore" pictures so that offending details were obscured.  Agnolo Bronzino's Allegory with Venus and Cupid (c1545) was bought in Paris (together with the Garofalo) in 1860. It was painted for the erotica-loving French King François I. Its last French owner, Edouard Beaucousin, kept it concealed behind a veil. A naked Venus, half kneeling, half seated, fills the foreground. Her parted lips are kissed by her contortionist son Cupid, who fondles her left breast. In the background, various allegorical figures represent the bad byproducts of carnal love. The National Gallery's first director, Charles Eastlake, thought the picture perfectly moral, but knew "clergymen & others" would not, so his restorer obliterated Venus's searching tongue and the nipple peeking between Cupid's fingers. Unbeknown to Eastlake (and only revealed by the 1958 restoration), the picture had long since been supplied with a veil occluding Venus's sex, and a myrtle branch covering Cupid's bottom. Even today, Bronzino's Allegory remains the gallery's most sexually explicit pin-up. It became newsworthy once again in the Aids-obsessed 1980s, when the distraught man behind Cupid was said to signify not jealousy or despair, but tertiary syphilis.  This year has seen concerted if uncoordinated attempts to redeem Bronzino, and to identify hidden depths. In January New York's Metropolitan Museum assembled his few surviving drawings to disprove the long-held belief that he was a mediocre draughtsman who was only at home with slick and shiny oil paint. And now, until January, 54 of his 70 paintings are at Palazzo Strozzi in Florence. These are his first ever museum shows.  The drawings were a very mixed bag, but the wonderfully paced Palazzo Strozzi exhibition is a revelation. Bronzino has been recast. He is no longer just the arch mannerist, the etiolated epigone of Michelangelo, perverse and stylised in equal measure. In his bourgeois portraits, we can admire the verve, inventiveness and psychological oddity; in his religious works, we can find searching anatomical realism and sense the storm clouds of the Reformation. Rather than representing the final fetid flowering of Florentine painting, Bronzino now seems like a mesmerising and hyperreal precursor to Caravaggio. (Nothing though, can redeem his tapestry designs and frescoes.)  Agnolo di Cosimo (1503-72) was born into a poor family near Florence. In the 1530s he adopted the nickname "Il Bronzino", a widespread practice in cultural circles (a poet friend was called "Il Lasca" – the cockroach). His new name may have referred to his bronze-coloured hair, but it also evokes the sculpted feel of his figures. He was apprenticed to a leading Florentine painter, Jacopo da Pontormo, and worked with him on frescoes and panel paintings. One of the most important lessons Bronzino learned was the expressive foreshortening of torsos, arms and hands, seen obliquely as if in a distorting or convex mirror.  A key catalyst in Bronzino's evolution was his trip in 1530 to Pesaro, on the eastern coast of Italy, where he worked on frescoes at the Duke of Urbino's Villa Imperiale. Bronzino's earliest surviving court portraits date from this period. He combines the poise of Titian with the high definition linear detailing of Holbein and northern Renaissance art. There's little of the flightiness of Pontormo, where everything aspires to the condition of a flag, flame or cloud. Bronzino strives for a tighter and tauter fit, verging on the claustrophobic. Naturalism is reined in by quasi-heraldic colours, contours, patterns and shapes. His power-dressed women both seduce and awe.  Bronzino returned to Florence in 1532, just as Michelangelo, in partial protest at the Medicis' seizure of power, was moving permanently to Rome. From 1539-55 (when Vasari supplanted him) he was the dominant artist at the court of Duke Cosimo I de' Medici, who took over after the murder of Alessandro de' Medici. Bronzino created the official images of the ruling family. A splendidly robotic half-length shows a bare-headed Cosimo right-side-on in state-of-the art armour; 25 versions exist – a small army. In political symbolism, the ruler's right arm signified his military and judicial might, while the left arm (closer to the heart) signified his liberality. Bronzino foregrounds the ruler's right arm, inflating the forearm as it cantilevers across his chest to take possession of his helmet. Cosimo stares up and away to his right, as if eyeballing his Maker. His left arm is all but invisible.  Cosimo was an able bureaucrat, not a soldier, so the armour is fancy dress, but this image says "invincible Machiavellian prince". Cosimo's armies subdued the whole of Tuscany, and he unflinchingly ordered the torture, execution and assassination of his republican enemies. As so often in Bronzino's work, Michelangelo is co-opted. The marble David flanked the entrance to Cosimo's Florentine HQ, and Cosimo is a metallic reverse mirror-image.  In the famous double portrait of Cosimo's beautiful wife, Eleonora of Toledo, with their two-year old son Giovanni, her left arm and hand are foregrounded. There's a tantalising promise of liberality, in the cascading satin dress with its embroidered pomegranate motifs, and in Eleonora's long lilly-fingered left hand languidly toying with the seed-pearl tassel (possibly deigned by Benvenuto Cellini). The basic format, of a woman seated on a balcony, is inspired by the Mona Lisa, and there's a watery landscape abutting Eleonora's left side, that recalls a popular metaphor, the "lake of the heart"; there's even a left-sided half-smile. So far so friendly.  Counterbalancing this is the quasi-Egyptian inscrutability of her eyes; the mask-like ivory oval of her face; the light blue halo effect around her head; the shield-like rigidity of her bodice; and the chain-mail of her pearl and gold partlet. Eleonora would have to be Houdini to undress herself. The catalogue entry drily notes that the dress is a form of product placement: "a virtual advertisement of the duke's revival of the silk industry in Florence". She was buried wearing it. Only Ingres and Matisse have painted patterned textiles with such insistence and panache.  Bronzino's Medici portraits express their divine right to be dynastic rulers. And Bronzino was a believer. He wrote heartfelt petrarchan sonnets extolling his employers, and in 1551 wrote awestruck from the reconquered Pisa, while painting the ducal children: "I am continually with these most saintly sovereigns, and I rejoice in the blessed sweetness of so good and benign a prince." Giovanni de' Medici was destined for the church, and in the double portrait, already thinks of higher things. His head is shaped like a dome on a drum. His forehead, haloed by golden ringlets, is high and far more bleached than Eleonora's. He is a rising sun to his mother's full moon.  Bronzino's seamless blending of the sacred and the secular eventually drew the fire of Counter-Reformation critics – he included portraits and portrait-like figures in religious works, above all in the spellbindingly risqué altarpiece Descent of Christ into Limbo (1552). This is a renaissance nudist camp with its three sultry sirens to Christ's left: "Whoever stops to gaze at this painting," complained one critic, "cannot but feel some stirring of the flesh."  A compelling room in Palazzo Strozzi is devoted to Bronzino's commissions from the diplomat and poet Bartolomeo Panciatichi, a French-born Italian who developed Protestant sympathies while frequenting the court of François I. He returned to Florence in 1539 having married Lucrezia Pucci, but regularly visited France – he may have brokered the deal for the Allegory of Love. From Bronzino, Bartolomeo commissioned three religious paintings, and a pair of portraits. Lucrezia is transformed into a sphinx-like objet de luxe. Her ivory neck and face rises like a stamen from her red satin dress, perhaps evoking the Florentine fleur-de-lis. She is framed by an arched niche made from grey pietra serena. This tour-de-force was the catalyst for the maudlin meditations of Milly Theale, the American heiress heroine of Henry James's The Wings of the Dove. For Milly, Lucrezia was "handsome in sadness . . . unaccompanied by a joy. And she was dead, dead, dead".  Milly's last sentence makes far more sense in relation to the recently rediscovered Christ on the Cross (c1540), also commissioned by Bartolomeo. James must have read Vasari's account of the Panciatichi commissions, and Milly's view of Lucrezia's portrait was surely influenced by the gruesome way in which Bronzino created his altarpiece. Having painted portraits of Bartolomeo and his wife, "so natural that they seem truly alive", he "painted a picture of Christ on the Cross, which is executed with much study and pains, insomuch that it is clearly evident that he copied it from a real dead body fixed on a cross, such is the supreme excellence and perfection of every part".  The cross in Bronzino's picture is set starkly, like Lucrezia, before an arched pietra serena niche. Christ's scrawniness, and slumped head, hark back to austere 15th century examples by Donatello and Masaccio; his isolation, and the absence of other saints, accords with the Lutheran emphasis on Christ and his passion. Lucrezia now appears to be less the bride of Bartolomeo than the bride of Christ – the red of her dress matching the blood dripping from the base of the cross.  Bronzino was a respected poet, and most of his Florentine sitters belonged to the cultural as well as the social elite. They are flanked by a book, statue or statuette, and furniture with carved decoration. Many sitters have momentarily broken off from reading. When we look at these portraits, we enter an ivory tower. These tasteful displays of cultural capital were partly due to etiquette books such as Castiglione's The Courtier (1528). But in Florence, the arts were also beginning to be seen as playing a vital part in asserting regional identity. Cosimo de' Medici saw the political and economic advantages of highlighting Medici patronage, past and present. One of Bronzino's first commissions was to paint a portrait of Dante, and his big religious paintings included portraits of famous Florentine writers and artists, including Michelangelo. We don't know much about his religious beliefs, but he certainly observed the new religion of art.  Yet these cultural props are vital for a completely different reason. They introduce a sense of contingency and conversation. Without them, Bronzino's sitters would be little more than aloof, taciturn marionettes. The presence of statuettes, carved grotesque decoration, and sometimes even dogs, fills the lower half of his pictures with sets of other eyes, looking in diverse directions. It's a kind of ocular subconscious. We become connoisseurs of eyes and (with headless statuettes and veiled grotesque heads) of eyelessness. When, newly sensitised, we look back up into the eyes of his sitters, we notice that they often diverge – so much so that the boy in the magnificent Portrait of a Young Man with a Book is routinely said to suffer from strabismus, a condition where one eye focuses normally while the other "wanders". Yet this is a trademark of Bronzino's bourgeois portraits. Folklore traditionally frowns on divergent eyes. But in Bronzino, the presence of truant eyes is liberating as well as creepy. They imply the existence of secret niches for the imagination.  Bronzino: Artist and Poet of the Medici Court is on at the Palazzo Strozzi, Florence until 23 January 2011. www.palazzostrozzi.org
Bronzino has often been disparaged as the arch mannerist. But, as James Hall argues, his portraits of the Medici court are a revelation – mesmerising and inventive