Beauty is in the eye of the teddy owner

Piero della Francesca's Baptism of Christ, one of the most visited (and loved) paintings in the National Gallery, London, shows Jesus standing in the river Jordan; whereas many artists sheathe the saviour up to his middle in the waters of baptism as if in a translucent cocoon of Fortuny-like wrinkled gauze, Piero paints his feet, in a puddle, on a patch of silted river bed apparently at the water's edge. This meagreness has given rise to much speculation: does it suggest the exhaustion of the Judaic writ, does it mark the break between the Old Covenant and the New? Martin Kemp, in this pugnacious study, dismisses any such symbolic hermeneutics. With a background in the sciences and expertise in Renaissance geometry, physics, optics and the like, as displayed magisterially in his edition of Leonardo da Vinci's writings, Kemp draws attention to Piero the mathematician, and argues with dazzling persuasiveness that the artist was attempting to paint a trick of light on water: in certain circumstances, here brought about by the effulgence of the hovering Holy Spirit above, a surface ceases to reflect and becomes translucent.

Kemp illustrates this effect with photographs of rain-soaked city pavements and a channel or ditch that he has taken himself. Thus Piero's Jordan does not flow with esoteric reference, but documents a common natural phenomenon of visual experience: the artist's genius lies in his pushing optical inquiry further than any of his predecessors (or indeed, successors) within the limits of contemporary Renaissance knowledge. (Oddly, walking past St Paul's Cathedral on the wide smooth pedestrian parvis after a shower of rain last year, I was enthralled to find myself suspended 200 feet above the vision of the dome upside down in the puddles: a conjunction of meteorological conditions I had never before experienced, but similar to the one Piero was recording.) The pages on Piero's Baptism demonstrate Kemp's unique combination of skills at their finest. It is consequently a great pity that they remain exceptional in this book. Behind the Picture concentrates on many famous works of the Italian Renaissance - on Fra Angelico, Masaccio, Mantegna, Michelangelo, Leonardo - and at times reads like a book version of Kemp's Italian Renaissance course. But its burden is above all polemical: Kemp is issuing a manifesto for art history as he professes it, against all others. He lays about him, a historical materialist with sharpened secateurs, snipping at the Warburg school of metaphysical and literary exegesis, pollarding the College Art Association's profuse growth of new historicism, semiotics, psychoanalysis, queer and gender perspectives, pruning those eager shoots of theoreticians who presume to find gay power relations in Mantua or Rome. His favourite epithet is robust, and so, robustly, he denounces the idea that an image can be "read", that a picture is a text, and suggests instead that the verb "to prospect" should be adopted, with its overtones of scientific surveying of territory, of gauging and measurement and panning for gold. He does not use it much himself, however, and contrary to his professed denials, lapses into "reading" a composition (with regard to Titian's Christ and the Adulteress, for example).

The opening chapter reproduces a battered teddy bear that remains undiminished in its child owner's eyes, despite its losses of feature and fur. Kemp offers it as an image of his self-appointed task: "A significant facet of the historian's art consists in drawing our attention to the equivalent of the loss of the teddy bear's features - that is to say, heightening our own perceptions in ways that visual and conceptual frameworks of the original users and viewers might not have accomplished - but this awareness needs to be accompanied by at least as powerful a sense of why the teddy's 'patron' was oblivious to its impairments." The historical record is likewise damaged, splintered and spotty, and can never be fully repaired. Gaps, not traces, dominate our prospect of the past; the map of history is an accidental desert, where a single surviving rock may misleadingly appear an important, intentional monument.

With more than a touch of the Gradgrind, Kemp demands that art historians attend to the available evidence, as he does, in order to reconstruct the historical specificities. He is very strict: there is to be no anachronistic speculation, absolutely no fancy or colour in the struggle to conjure "a whiff of reality". Legal documents and notarised contracts, bills for paint and materials and the cost of frames, fees of artists and prices of antiques are marshalled in order to deepen our grasp of the difference between the past and the present and reimagine the cherished teddy and its owner.

This Braudel-like inventory of an artist's working conditions delivers much invaluable, knobbly, archival information, and Kemp excels at analytical readings of artists' writings, including Piero's De prospectiva pingendi, and at recovering the resonance of words, such as ingegno and fantasia, which do not match our "genius" or "fantasy". His learned range does not altogether exclude some vivid story-telling: Mantegna's commission for the Madonna della Vittoria, placed back in context of an anti-Semitic incident in Mantua, loses its innocence as a work of art; the complexities of Michelangelo's disorganised career flicker into life as Kemp dismisses the sonnets as evidence in favour of the artist's correspondence and business troubles.

Such revelations are hard won, however, and much of what Kemp presents does not much change the prospect for anyone who stopped believing. The Agony and the Ecstasy was a true report on an artist at work. The word art itself was still attached to its Latin meaning, of craft or skill, with overtones of secret ingenuity and special knowledge (Prospero is still using it in this way when he refers to his magic), and was not invested with the individualist value accorded to it today. Artists were journeymen, jobbing for contracts and working in botteghe, conditions that complicate the idea of personal signature. Renaissance princes paid fortunes for classical bibelots and antique gems but quibbled over paltry sums for works we consider sublime. Mantegna and then Leonardo struggled, successfully, to change all that and gain lofty, even noble status for the profession, and the word art began to acquire its present exclusive meaning. Paintings fulfilled a function that is defined not by their beauty alone but emerges (partially) in relation to patrons, siting, religious and political purposes. Thus Fra Angelico's many different versions of the Annunciation suit the audience for whom they were intended, and the processes could be fairly haphazard. An obscure saint, like Mamas, appears because he is a favourite with one of the paymasters, not for any deeper reason of piety or symbolism.

In reconstructing the past, common sense rules. The mysterious Botticelli of a maiden with a centaur might have been commissioned thus: "Lorenzino wanted an attractive painting to decorate his room and asked Botticelli to come up with something appropriate - 'you know the kind of thing, a pretty woman in one of those rather naughty Roman dresses, like the one you did for my uncle, but not as wide because it's got to fit above the door."' When Isabelia D'Este drew up detailed iconographic schemes for Perugino to follow, she was a meddling pest; her complicated, discursive ideas made life impossible for artists who did not usually work to such literary specifications (Kemp passes over in silence some notable successes that resulted from her patronage - Mantegna's Minerva driving out the Vices from the Garden of the Virtues and a pair of delicious, sensuous Correggios).

Kemp's assault on current tendencies to heady hypothesis and occluded meanings, on reading pictures beyond the character, epistemology and practical restraints of their context, rings with a sincere teacher's desire to bring attention back to the works themselves, and to make students, intoxicated with modish theory, resume hard detective work in the archive, where Piero's mathematical speculations, for example, lie dusty and uncherished. But there are many problems with this disputatious and partisan approach. Kemp's writing is pedagogical in tone, failing to catch fire: he displays none of the feuilletoniste's fiery bravura, the Marxist's indignant eloquence, the Lacanian's rapture, the mythographer's passionate curiosity; he often adopts a sobersides, itemising, QED rhetoric that can be numbingly congested. He implies, ignoring the contributions of any number of practitioners, that all the opposing schools of art-historical exegesis do not attend to the material and social circumstances in which the works were made and overlook the stubborn particularities of the past. This is not only wrong-headed, but profoundly ungenerous. Of course excessive, obscure fandangle befuddles the discipline here and there, but mistaking it for the whole is tantamount to reading David Lodge's Small World as a historical account of the state of Lit Crit. Kemp is reportedly involved in a huge show about the body, planned for the reopening of the Hayward Gallery - if it ignores recent thinking on this theme, it will not only be foolishly Luddite, but, worse, it will be dull.

Setting aside these problems, Behind the Picture oddly fails to fulfil the criteria Kemp himself sets for the prospective interpretation and appreciation of art. He insists, rightly, that one of the differences between a text and an image is that a painting cannot be fully translated into words, that explanations ultimately collapse in the face of the thing-in-itself, and that the mysterious effect of a work of art, experienced most frequently today when seeing something in the flesh that was previously only familiar from reproduction, is the source of inexpressible pleasure (he could use the word jouissance, but of course he will not). "In the final analysis," he writes in the concluding lines of the book, "the experience of the artefacts of past and present cultures provides for me a sense of joy of a specifically visual kind. Such visual experience touches areas of conscious and unconscious thought in which words are able to act only as very coarse filters."

Unimpeachable sentiments - except that Behind the Picture remains behind the picture to such a degree that the works under discussion hardly figure, let alone the joy they bring. The enumeration of business details, the informed discussion of critical writings, the history of the social position of painters, the analysis of patronage, sideline the art itself as a source of joy. By giving insights into the changing history of evaluation, Kemp abdicates offering principles of his own by which to evaluate: he cannot mean that aesthetic pleasure lies altogether beyond expression, yet no amount of jaunty speculative anecdotes, notarised documents or invoices for gilded frames will explain it.

This collapse of judgement brings about the most peculiar results: limiting the investigation of meaning in accord with available data flattens the works of art in relation to one another in a paradoxically postmodern manner, so that nothing is better than anything else, only better documented and hence more accessible for discussion. Second, many of the illustrations, including the cover showing a detail of Mantegna's Camera degli Sposi, are not discussed, and consequently feel like redundant ornament, there simply to entice the reader. One longs for less of the Sistine chapel in full colour and more relevant, accompanying images that advance the argument: the reproductions of Leonardo and Michelangelo's manuscripts, Kemp's own diagrammatic demonstrations of perspective theory, his photographs of reflections in water, the grand house Mantegna built for himself, are vital and illuminating; there should be more such examples of the evidence he values, of the letters and invoices and contracts and manuscripts with which his arguments are underpinned. He wants us to attend to the material character of artefacts to understand their function, but his own book proceeds at cross-purposes, a salvo from the trenches of the art-historical culture wars travestied as book-packager's product.

Marina Warner is author of From the Beast to the Blonde: On Fairy Tales and Their Tellers.