Visual arts: The secret power of kiss and tell

Modern art criticism has often issued this firm reminder: we must never forget that a picture is a flat surface. That's perfectly true, and many viewers have taken it to heart. A picture is made of lines and shapes, tones and colours. But if we dwell too much on the all-over surface flatness of a picture, we may miss something else: its outbreaks of local flatness.

A picture is a place where isolated incidents of flatness may suddenly strike, even though the image is otherwise strongly committed to creating a sense of depth and solidity. This sets up powerful conflicts and tensions and pressures. It can happen in a single object.

Imagine a sphere. In a two-dimensional image, it's depicted as a round shape - but a round shape which could also just be a flat circle, face- on. And a picture could handle this round shape quite ambiguously. At one point it could treat it as a globe, showing a spread hand laid upon its rotundity; but at another point it could treat it as a thin disc, with a hand pinching its edge between finger and thumb. It would become an impossible object with contradictory properties, a trick figure, and the kind of thing we expect to find in joke or puzzle-pictures. However, the trick is really a basic resource of any picture. It provides the decisive effect in images whose subjects range from kissing to killing.

Sometimes it is a joke - a food joke, for instance, about greed and hunger. There's a painting, which may be by Pieter Breughel the Elder, called A Fat Man and Two Thin Ones (A). It's a picture of three heads, two starvelings and a stout friar. One of the lean ones is taking a bite out of the complacent friar's cheek. It's an impossible bite; or rather the bite makes it an impossible face. With such a meagre nip, you wouldn't get your teeth round this plumpness, unless the face itself were as flat as a pancake. That of course is the picture's joke: on one side of his face the stuffed monk turns into a round pie. Eat the rich! And while the unbitten side stays solidly chubby, the bitten side gets a shallow rim-like shading round its edge, to stress this flattening.

Icon paintings often treat every figure as a cut-out shape. When their figures come into contact, they behave as paper-thin flats: they overlap and interleave and slot together, sometimes in a complicated origami. Take the cheek-to-cheek embrace in a 16th Century Moscow Virgin and Child (B). It uses a simple overlap. But they're both such slivers that if, instead, the Child's head was tucked behind the Virgin's, instead of in front, there'd be no sense of strain. What's touching in such images is the way this sliveriness allows a more than human closeness - for no one ever truly stuck to anyone like a stamp to a letter.

The icon's cut-out world is uninterrupted. But some pictures have it both ways. And when embracing figures are arranged in a flat and over-lappy way, yet are also shown as having definitely solid bodies, things start getting tight. This is what creates the feeling of snug intimacy between faces in Two Lovers (C), a painting by the Venetian artist Paris Bordone. To judge from the volume and stance of these bodies, their heads could not really fit together, one just behind the other, as they are pictured. If you made an accurate three-dimensional model of the figures, you'd find their heads actually shared some of the same space, very slightly interpenentrating.

But for the purposes of bringing them together, Bordone proceeds as if the figures were not at this point resistant solids, but flats to be slipped one behind the other. You feel the slight contradiction - it is essentially the globe/disc switch - as a slight squash. And the intimacy is quickened by the way the woman's left eye is just caught between the lines of her nose and his cheek.

Kissing mouth-to-mouth isn't so often pictured in European art. It's somehow an awkward subject, perhaps connected to the way kissing faces get lost from sight, and when it appears it usually shows awkwardness - happening in ways it couldn't quite happen.

For instance, like this: sometimes in a picture spatially remote figures appear to meet. The effect is called "false attachment". One figure is set some way behind another - yet their edges touch, coincide, and they too seem to touch. You find it, for instance, in a detail from Piero della Francesca's Legend of the True Cross frescoes in Arezzo (D), where two distant cheeks (as it were, unknowingly) brush. And it's with a more insistent version of this device that Giotto paints a kiss.

Some Christian legends say that the Virgin Mary was herself not conceived through the usual channels either, but simply through a kiss between her parents, St Anne and St Joachim. Giotto shows this kiss in one of his scenes in the Arena Chapel, Padua: The Meeting at the Golden Gate (E). There's something not quite sure about it. You might think their faces hardly meet. They hug, and their profiles cross, forehead firmly set behind forehead; and Giotto - famous for it - models these heads with sturdy solidity. Their mouths should pass each other by. Yet their mouths' edges, exactly coinciding in the picture, are suddenly brought together (by a false attachment), and sealed lip-to-bearded lip.

You can feel this effect in different ways. If you take the mouth-contact as the sure thing, it bonds the heads in impossible union (emphasised by the way that, together, they make a single face, with a single pair of eyes). But if you focus on the heads' solid separateness, then it's the kiss that shows up as the impossibility, a miraculous bodily slip (rather like a miracle-pregnancy).

This kind of kiss recurs. You find it done lightly in an early Chagall, his Pair of Lovers (F) of 1916. The woman's head is turned around, but the trick is the same: profiles overlapped so that mouth directly, impossibly meets mouth. The effect is less miraculous because Chagall's figures are such miraculous creatures already, weightless and whispy, like spirits or angels for whom interpenetration is quite the normal thing.

And you can find a stormy version by the Irish artist James Barry, in his Jupiter and Juno on Mount Ida (G). It's an image of sexual hatred. The crossing-profile effect is similar, with the woman now on top. But the mouths don't meet - and that's the point. A kiss is determinedly resisted, even as other pictorial devices are busily jamming and fusing these two heads unwillingly together. Like the Giotto mouths, Jupiter's nose "attaches" to Juno's upper-lip. The head-gear - his head-band and her chaplet - seems to join in a single arc. Most striking are the eyes, which you can't but see as both eye-balling each other - and at the same time rigidly averted. The flattening strains now work not for miraculous intimacy, but resentful emotional bondage.

There are further, more distant, variations. In a drawing by Thomas Rowlandson, The Kiss (H), you can't quite say who is behind whose shoulder, whether the kiss is open or "stolen". But it turns out the lady and the gentleman are partly joined like jigsaw pieces, her neckline and his under-chin sharing a single edge, making it impossible to read both figures simultaneously (just below that point, the bodies are lost in a confused blur). And in fin-de-siecle images you find passionate fusions approaching symbiosis.

In Munch's woodcut The Kiss (I), from 1902, bodily identity is reduced, beyond cut-out flat, to mere shape-contour. The face contours merge completely, like egg-yolks in a bowl; the body contours merge too in a single shadow- stencil. Klimt's The Kiss (J), of 1907, is a more elaborate variant on this.

Unlike Munch, Klimt introduces a suggestion of palpaple flesh into his tight arrangement of lovers. The faces and hands do seem embodied. But then he leaves you wondering what volume and what position the bodies occupy, underneath that flat spread of ornamental fabric; and how they fit, inside their containing, amoeboid contours.

The answer is that no sure distinctions can be made - and only a two- dimensional picture could present this particular fiction. Klimt's bodies are simply, unimaginably congruent and identical with the ornate, curvy cameo into which they're locked. They're all it, it's all them. And Klimt uses a strong locking device. As the man's head swoops down from his shoulders like a vulture's, it ends up entirely enclosed in the body shape. It's another old trick: compacting.

Compacting is a kind of foreshortening. It's one of the things foreshortening does. Foreshortening can create impressive depths, showing bodies sharply receding, like the prone corpse-in-armour in Ucello's battle scene. But also, especially when it shows things exactly end-on, it compacts. It's not just that a long thing is seen from a steeper angle and so looks shorter. It looks reduced, compressed. Lines become points (an arrow seen tip-on), circles are squared (a chariot wheel, hub-on), the crooked is made straight (a bent arm, elbow-on). It's as if the normal shape of something had been put under a pressure, forced into a stricter form, like a compacted car.

Compacting is like flattening, but operates on another axis. Flattening squashes depth. Compacting squashes shape. And when applied to bodies, its strongest device is to incorporate heads - to show the figure head- on so that the head is integrated into the body. In Breughel's Gloomy Day (K), the wood-gatherer's head is gone completely into his torso. The effect is to submit the man to his labour. You may say that, realistically, the figure is just shown bending down. But it could have been shown bending more sideways (like Millet's Gleaners). The sinking down of the head inside the body's contour, the removing of the head as a distinct, independent entity, is a powerful alteration to the human shape.

There are degrees. With one of the damned in Michelangelo's Last Judgement (L), a struggle continues. The head's shape is still just free of the shoulders' enclosing edge. The damned figure is falling, but not quite crushed. This semi-compacting is inherently tense, in both a muscular and dramatic sense, a position strenuously held. But it is wrong to give any pictorial device a fixed specific meaning. It has potentials, which are up for use.

William Blake, for instance, has a use for the full head-down - as in an image from Jerusalem (M). It's an embodiment of psychic bondage, and the figure is literally bonded to itself - not only compacted into a quasi- square, but flattened also. The top of the knees exactly coincide with the outline of the shoulders and so "attach" back onto them. The whole body-unit feels cast and stamped like a coin.

Among the Mexican Muralists, on the other hand, the main use isn't bondage but a sort of self-solidarity, a simple moral sturdiness, which isn't far from cuddliness. There are several examples in Diego Rivera's work, but the epitome is an etching by a lesser known Mexican artist, Jean Charlot - First Steps (N) - where the mother's body becomes a snug mushroom, each body-part rounded and parcelled in. Frankly ridiculous.

Both these formations are stable. But the head that emerges just out of the torso-contour introduces a strain. In Munch's The Sick Child (O), this is the picture's point of grip. The scene is a head drama. The child's head lies in pure profile - frail, flattened, fading. The older woman, bent, presents her head head-on. It is lowered so its back is precisely level with her shoulders; it attaches there, sets rigid. However, it resists complete containment, extending out to the side. It's a tense, L-shaped hold, tokening a desperate holding on. Likewise in Kathe Kollwitz's Battlefield (1907) - where a woman searches in darkness for her son's face among the dead - the head just - only just - breaks the formless silhouetted lump of the body - a barely surviving humanity.

But the compacted head can be put to much stranger effects. I suppose the woman in Bonnard's Nude in a Bathroom (P) is some sort of relative to Blake's bonded man. Here the stopping head is both contained and aligned/attached to the shoudlers' curve. And then the whole body - save for one stray arm - is figured in a tight, tapering shape, which narrows at the feet to a point. It looks like a tadpole. The body stands, top heavy, precariously balanced, teetering on its tip.

Or take the figure of the airborne hero in Veronese's Perseus and Andromeda (Q). He is poised to strike, mid-air. He flies quite un-aerodynamically. He has a purely pictorial form of support. His body, head incorporated, is held in a compacted shape. He looks in short less like a flying man, more like a flying machine - not unlike one of Leonardo's - his limbs performing like working parts. But then what finally keeps him in the sky is his foot work: one foot just off the building-skyline (a toe on the bottom), the other sticking to the picture's edge like a fly.

All these versions are in some way consolidating. But there are pictures where the head is incorporated means - in one sense or another - that the head is lost. Goya is your artist for this. It's one of his specialities, the torsoed head, unmodelled and reduced to little more than a dark smudge. The famous etching in the Caprichos, The Sleep of Reason Produces Monsters (R), has one of these. The nightmare is not only in the nightmare creatures, but in the effectual absence of a head that might ever wake up.

And in a later drawing, The French Penalty (S), Goya stages a guillotining. Many of Goya's cruelties are torn between outraged pity and black comedy. Here, as often, it's hard to say. Head-on, the condemned man becomes a helpless bodiless mop, a mere cipher of a man. And then, this head intimates its own imminent severance: its dark round patch is easily mistakable for the empty hole of the guillotine's collar.

It's a pictorial pun, not between solid and flat, but solid and void. It's hard to get the tone of the pun, but its point is clear: an utterly casual indifference between life and death: could see it one way, could see it the other - before/after, head/no head - no matter.