After you, master, after you

Frank Auerbach attempts to link the past with the present in his modern-day interpretations of Rembrandt, Rubens and Titian. Tom Lubbock finds it all rather puzzling

The National Gallery has rather straightforward ideas about keeping up tradition. It likes it when distinguished artists of the present day come in, and do new, in-their-own style versions of pictures in the collection. It takes on Associate Artists and gives them a studio in the building in order to foster these visible connections between past and present; to say, look we're alive!

Frank Auerbach is not one such artist. He hardly ever does that sort of "project'', but he's been a great user of the gallery. He goes there and makes drawings from pictures, and mostly this is for inspiration, as an aid to working things out in his work. Sometimes, though, these drawings have been used to make paintings specifically "after'' other paintings. Over the years he's done this with a Rembrandt, a Titian and more recently with another Rembrandt and a Rubens.

These paintings, together with a mass of drawings, are now on display: "Frank Auerbach and the National Gallery: Working after the Masters". It's a puzzling business.

I may as well admit that even in the normal way I don't really know what Auerbach's doing when he paints something. Some experience of his subjects (sitter in the studio, view outdoors) is being grasped and rendered in those often hardly legible swerves and bolts of pigment - but the motive seems to be neither visual nor psychological; not a reconstruction of the complexities of perception, not expressive distortion. You can sense a struggle and find the results intensely vivid, solid and delightful without seeing what the terms of engagement are.

But whatever they are, I'd have supposed they wouldn't grip if the matter in hand was itself a picture. For isn't his painterly struggle provoked, somehow, by the living substance and the changeability of people and landscapes? (He never does still lives.) How does that figure when the subject is already flat and fixed? For viewers, on the other hand, this fact may be a help. We can't ever know just what the experience was in the studio or out on Primrose Hill. But here we follow him. We can see the old paintings and then see what he's done "after" (with, to, from) them. Something might get clearer.

The earliest of these revisions, from 1961, takes off from Rembrandt's small Lamentation over the Dead Christ and takes off far. Enormously bigger, browns and golds gone monochrome, it involves a drastic formal reduction in which all the verticals and diagonals become an elementary linear scaffolding. The crucified thieves vanish. The sole figurative remains are the Deposition group at the bottom, deposited in cold, fat whites. But cross-reference back to the Rembrandt shows in fact that it's not essential. Only its gravity is remembered. This is a new and independent picture.

It's not quite like that with Bacchus and Ariadne (1971). Titian's stop- motion event is here a confusion of those stick figures Auerbach sometimes puts in his landscapes - such a confusion that you immediately look to the Titian, but even then it's nearly impossible to decipher. So many of the strokes are zapping bits of energy. The colours have gone wild. You start to give up on correspondences. It's gone beyond being a commentary - still, not quite far enough beyond. The picture goes entirely on its own road. It's in a half-dependency, not fully in communication with the Titian, not quite re-created either.

In the recent re-workings from Rembrandt's Belshazzar's Feast (1990) and Rubens' Samson and Delilah (1993) the dependency is more thorough, and in the end awkward. The Belshazzar is partly an improvement - it gets a dynamic twist into the king's sudden gesture which in Rembrandt is stiffly effete - though the story bit is hard to keep alive. Rembrandt's glimmering writing on the wall can't be omitted, but is rendered literally as "WRITI NG ON T WALL" (sic), roughly lettered in a cartoon speech bubble; an odd sort of joke again, where nothing else is.

The two versions of Samson are also close, when you sort them out. They look like their original: Auerbached and losing its point in the translation. They prove that Rubens' drama can't survive this kind of re-rendering. It depends on its nuances of facial and bodily expression, of lighting and texture: precisely what Auerbach is bound to leave out.

Auerbach has said about this Rubens (it's up on the gallery wall): "The great purple knot at the top, like a tear, underscores the fleshy drama with an accompaniment of poignancy and waste ... it's quite obvious that she's betraying him, that he's ruined and that she loves him", and that's well said. But it's obvious, too, that this is not the kind of thing one would ever say about a picture by Auerbach. He works from a quite different base.

What sort of connection between past and present is established here? It's most alive when most remote, when - as in the Lamentation picture - the memories are distant and we aren't teased with those intimations of likeness that only point to what's gone. The Bacchus and Ariadne, too, really bizarre as it is, wins something from its suggestion that Auerbach has caught the mythical incident happening again on Primrose Hill. Some of the drawings are terrific.

More Auerbach can be seen at the Scottish National Gallery of Modern Art in "From London" - a big group showing of the "School of London" - or rather, "the so-called School of London". It was named by the painter RB Kitaj almost 20 years ago, grouping together Auerbach with Francis Bacon, Lucian Freud, Leon Kossoff and Michael Andrews (who died a fortnight ago), and ever since then it's been contested. Whether or not there is really such an entity, the coinage was undoubtedly canny.

By now, the slogan has surely done its work, at least in Britain. Each of those artists is as famous as need be, and the grouping has become a cliche. So "From London", which features the core six, feels simply belated. If it's a representative selection of work by those six you want to see, then fine; it's very well chosen and very well displayed. But it's time to be making new comparisons.

n 'Frank Auerbach and the National Gallery: Working after the Masters' until 17 Sept. (0171-839 3321); 'From London' at the Scottish National Gallery of Modern Art, until 5 Sept. (0131-556 8921)