What are you looking at?

Nigel Hall looks distinctly anxious if you describe his work as beautiful. So perhaps I should start by saying it looks oddly sexy instead. I don't mean by this that Hall is one of those sculptors whose formal vocabulary gradually reveals itself as an elaborately sophisticated alternative to the female body. There are, it is true, any number of openings and vestigial passages in his work, and even the occasional lip, but if they were to suggest any physiological structure at all, it would usually be the eye. These are sculptures about the sensuality of looking.

It's a sensuality that takes many forms. There is, for a start, his use of Cor-ten steel. Not, you might think, a particularly erotic material, but then this is steel patinated with rust of a very particular soft, warm, honeyed reddish brown; looking at the long, flared, arching sheet of metal in Passage, you feel that this unyielding stuff has somehow been coaxed into a momentary pliancy. When, as in his Soglio series, he introduces a wedge-shaped vertical element into the smooth interior of an upright ring of steel, it comes as a shock to realise that the soft curve and the angular intrusion are made from the same material.

There is, in this ambiguity between hard and soft, straight and round, a hint of the formal tensions that make Hall's works linger in the mind long after their immediate prettiness has exhausted itself. There are moments when, just as you have been lulled into savouring their exquisite sense of stillness, you find yourself wondering if they are about to tear themselves apart, or simply to fall over. The ring form in Soglio VI is not a perfect circle but the truncated end of a cone, so that it stands not upright, but leaning back, away from the viewer. The upright element is not at the lowest point of the curve, but slightly to the left, so that you feel the whole structure should be rolling away to one side. Closer investigation reveals that the wedge continues right through the ring on to the floor, so that the destabilising element is also effectively locking the structure into position.

Again and again, in both drawings and sculpture, we find wedges and cones, apparently irreconcilable geometric elements, made to depend upon, and even define, each other.

Instability and dependence have been a concern in Hall's sculpture since the 1960s, something he has attributed to his childhood fascination with barrage balloons, the apparent tenuousness of the cable connecting its vast, voluptuous form to the ground. His works have often been made up of two objects separated in space, playing on the aesthetic tension between them just as much as on the journey of the viewer's body in front of and around them. It is no accident that one of his earlier works should have inspired an Richard Alston dance piece: it has the latent instability, and implied acceleration, of a sprinter on the blocks.

Even now, when his work has coiled itself up within its own containing contours, we find that the space around it has been colonised and dramatised: Big Blink, which seems at first sight so utterly self-contained, will look entirely different when we do not see, through and behind it, a corner of the gallery floor.

This is work of fantastic, almost fantastical precision; work whose formal resolution can depend on a detail as sharp as the momentary revelation, as one walks across the front of Soglio II, of a vanishingly small but distinctively rectangular sliver of white light dividing two vertical bars. Still, in more cynical moments, I find myself anxious that, though the appreciation of this kind of sculpture demands almost as much self- discipline as its construction, there is not, morally speaking, much to distinguish the whole exercise from the connoisseur's appreciation of fine wines.

To be "significant", in either sense of the word, we assume an artist has to address (if not actually to answer) identifiable issues - which may explain a certain touchiness over the question of "beauty": to say a work is beautiful sounds like a compliment, but is also the end of the conversation. I'm not sure what the answer to this is - I suppose you might argue that this specific work occupies a sort of metaphorical moral universe, a universe whose geometry is defined in terms of stasis and instability, of self-sufficiency and interdependence. You might well say that the inwardness of Hall's recent sculpture and drawings, with their flux between compass-drawn precision and hand-made awkwardness, and their studied ambiguities of interior and exterior, suggest a meditational impulse. Butthe most honest answer is that, while conceptual artists may challenge our perceptions, an artist like Hall can heighten and intensify those we have already.

This matters, not least because, as our critical culture generates, consumes and forgets ideas so quickly, it sometimes seems that none of them is allowed to test itself against our experience of the physical world. It's entirely proper to unearth distinct strands of intellectual curiosity in Hall's career, and follow them backwards and forwards over 30 years - but it's just as important to observe how those ideas have evolved as a function of his experience of the physical world. Discussing specific works, or even entire series, you find yourself referred to stimuli far removed from the confines of the gallery: to the horizon, to cliffs rising out of water, a glacier, a set of shelves. Others again have their roots in the craft, rather than the theory of his sculpture - in recent years, as he has learnt to appreciate the subtleties of the play of light on the birch ply he first saw simply as a malleable material for the making of maquettes, so his manipulation of light and shade, of the interaction of implied and physical planes, has become more and more sophisticated.

Nigel Hall, in other words, is not an artist whose work illustrates his ideas, but whose ideas are indistinguishable from his work. These are objects which only very slowly release their intellectual content, and very slowly bind you to them. They carry the authority of an artist gradually achieving an almost unnoticed maturity. And they're very beautiful, too.

n `Nigel Hall, Recent Sculpture and Drawings' is at the Annely Juda Gallery, Dering Street, London WI (0171-629 7578) until 11 May