They did not always love German art at the National Gallery. The Victorians went to extreme lengths to avoid it. When Gladstone bought the Kruger collection of early German paintings for the nation in 1854, as chancellor of the exchequer, there were dark suggestions that he must have been led by the nose. Two years later, an exceptional act of parliament was passed to make it possible for the gallery to sell it.
A whole altarpiece was broken up and scattered across the globe (many fragments have been reassembled for this show, an act of reparation twice over). Paintings by followers of Albrecht Durer and Lucas Cranach went back to Germany. Scenes from the life of Christ were dispersed, several ending up at the Metropolitan Museum of Art in New York.
Two world wars then put German art out of bounds for another 50 years. Cranach's Cupid Complaining to Venus, once in Hitler's private possession, and the backdrop for George Clooney and cast in their press conference for Clooney's film The Monuments Men, was bought by the gallery as late as 1963. A century with so few German purchases ought to produce a very nugatory collection and yet this is not the case, as this riveting exhibition reveals.
What did for German Renaissance art? Its strangeness, for one thing: starved bodies, broken limbs, tear-streaked faces, cold people in colder landscapes, the sheer starkness of emotion, the graphic clarity. The opening room shows exactly what the Victorians preferred, and chose for their new gallery: sweet-faced saints by Raphael, Aelbert Cuyp's cows down by the river, gorgeous Italian portraits.
When the curators did bid for German paintings, it was often in error. Hans Baldung Grien's searing portrait of a man whose hair seems to be turning silver even as you look was thought to be by the infinitely more famous Durer until the fake AD monogram was removed. The deep blue-green background behind the tough town clerk of Landshut spoke of Holbein until they cleaned it away.
And even when they did acquire a real Holbein - The Ambassadors - the eerie anamorphic skull tucked into the painting to haunt future generations was widely taken for a fish.
This tale of mistakes unfolds through the show. It seems impossible to believe that the Duke of Norfolk could have thought the tiny praying figures beneath Baldung's The Trinity and Mystic Pieta were his own English ancestors, given the tortured and angular Christ and the Teutonic Virgin, but perhaps he sensed something generally northern about the picture when he bought it in the 18th century.
For there is something in the cold grey climate glimpsed here and there in these paintings that irresistibly recalls our own.
It is there in the icy expanse of North Sea behind a Madonna, and in the lead-grey skies above a saint. And one senses its effects in the pale skins and occasional red noses of the people in these paintings, heavily muffled in velvet and furs. The show is rich in these insights, into a landscape of dark forests and rain-swept valleys, into an imagination alive to anguish and potent emotion, into a church dissenting from Rome, into the faces of Hanseatic tradesman and Swabian housewives.
The portrait of the Swabian woman of the Hofer family (her name is lost) is both poignant and comic. Her eyes twinkle, and her mouth is halfway to a smile, as if she knows only too well what the artist has done to her: on her copious white veil sits a black fly, positioned as conspicuously as a beauty spot. It lives - the illusion is superb - and it will die, like the brilliant blue forget-me-nots in her hand. Memento mori can be stultifyingly conventional (the skull, the candle), but these are so unusual as to be sharply arresting. And the fly is a proof of the anonymous artist's gifts too: a guarantee of the realism and fidelity of the portrait.
The National Gallery is blessed with these portraits. Lucas Cranach's fantastic picture of Johann the Steadfast, who must be steadfast in the face of harsh cares, shows a man strained and depressed. Perhaps he is already a widower. For his image is not paired with that of his wife but instead his six-year-old son, who will eventually succeed him as Elector of Saxony. The little boy is uncomfortable in his red-and-green slashed-silk costume and not quite sure what to do with his hands. It must be one of the very few father-and-child diptychs in renaissance art.
Strange Beauty, wonderful title, probably points to Matthias Grunewald and Cranach more than anyone else. Grunewald's female saints are wracked with anguish. Cranach's nudes are as far from the voluptuous beauties of the southern Renaissance as can be. His Venus is a slender, lynx-eyed siren wearing nothing but a fur-trimmed hat. The painting is a brilliant work of graphic design - the milk-white figure reaching up against the dark foliage, seductively serpentine, a cut-out just waiting for animation - with a comic punchline in chubby Cupid at her feet stung by bees as sharp as his love darts.
Cranach can move from the humorous to the profound in a single image without any loss of effect. His allegorical picture Charity depicts a mother patiently withstanding the demands of three pestering infants, one clutching at her thigh, while she feeds another, copied by the little girl with her doll alongside. The mother's face is loving and the lesson is clear: children learn early from our adult example.
The National Gallery has half a dozen Cranachs but was too late to the queue to buy more than one Durer (several more are among the 20 works on loan to this show). Still, it owns four great masterpieces by Hans Holbein, star "strange beauty". A Lady With a Squirrel and a Starling, long-nosed, bony and impassive, acquires character through the fantastic concatenation of shapes around her - the triangles of shawl and headdress, the quivering tip of her squirrel's tail, the whiplash branches in which sits a sharp-beaked starling. She springs to life in Holbein's art.
And the young Christina of Denmark, Duchess of Milan is portrayed against an expanse of that characteristic blue-green paint, her own lively shadow bringing her closer by measuring the narrow space in which she stands. Her face is brilliantly animated against all this flat colour, and the contours of black hat and costume only just contain all the energy inside her.
Henry VIII, hunting for a new wife, was famously captivated by this spry image; and looking at the portrait it is easy to believe in his predatory interest and her celebrated response. Christina is said to have quipped that if she had only possessed two heads, she might have given one to Henry.
Cupid Complaining to Venus, c.1525 by Lucas Cranach: 'a brilliant work of graphic design'. It was once in Hitler's private collection.
? Christina of Denmark, Duchess of Milan, painted in 1538 by Hans Holbein for Henry VIII, who was searching for a fourth wife: 'The contours of black hat and costume only just contain all the energy inside her.'
(C) National Gallery, London