Visual Arts: Here's one in your eye

Bridget Riley's paintings are renowned for their clever optical illusions. But would you hang one on your wall?

In 1967, when Bridget Riley gave one of her paintings the name Cataract, it must have been a tease. It's a wavy line composition, black on white, with just a hint of red and turquoise edging in. Lock into it, and it quickly starts to roll and shimmer out of any grasp. But recall that back then, Riley was cresting her fame as top Op artist, and part of that fame was the notion that her images aggressively eye-balled the passing viewer. So the title implies a pointed pun: not just a violent rush of water, but a nasty eye complaint. As if to say: oh really?

Sure, Riley's paintings never gave anyone cataracts, and witness is divided about whether they settle down on long acquaintance (eg, if you have one on the wall at home). I wouldn't even call the very dazzly black-and-white pieces from the early Sixties aggressive; peremptory perhaps, but that's alright. But evidently this is rather a touchy subject for the artist, and the Riley party- line sometimes comes pretty close to simply denying (in the teeth of plain evidence) that her work ever deployed optical effects at all. At any rate, Cataract - a very exciting picture, incidentally - was one of the last of the real wobblers. If you look at Riley's career as a whole, the direct eye-buzzing seems like a kick start, giving way to far richer and more subtle effects.

This you can do, in a way, if you go to Kendal, Cumbria, to the Abbot Hall Gallery, which is now showing a small retrospective: "Bridget Riley, Works 1961-98". Small, and not too well-balanced, it's weighted towards the Sixties and the early Eighties, but I suppose those are the best periods. Riley was born in 1931, found form quite late, and has pursued one of those rigorous, Modernist careers where less is very more-ish. In the Seventies, seeking a new start, she produced little. In the Eighties, she began painting vertical stripes. In 1986, bold diagonals entered her work. Recently, curves too have returned. Of course, put in this bulletin manner, it sounds rather absurd, but Riley's progress proves the old truth. Rules make free, and discipline is delight.

Take the multi-toned, grey-scale paintings of the mid-Sixties, in particular the four screen prints called Nineteen Greys (1968). They couldn't make themselves clearer. Their magic is the way they marry the perspicuous with the elusive. Each has a regular pattern of little grey ovals set on a uniform grey ground. The ovals are turned at varying angles, building up into the sort of very involved formation manoeuvres military bands do. They're also painted in very gradually adjusting shades of grey, going lighter and darker than their grey backgrounds, or going the same tone.

Strange illusions follow. Where the tones of oval and ground converge, it's as if a deep shadow or a smoky film were passing over the picture surface; where they most contrast, the ovals become cut holes, or shiny slivers of mirroring. Absolutely perspicuous it is; all these effects can be identified, and at the same time, never quite grasped. The pictures practise no optical fuddle, but they achieve a perfect trompe l'oeil. The shadows look like shadows cast, not depicted, and though you can analyse this illusion, you can't blink your way out of it.

Yes, really clever: that's the phrase that comes to me with those Rileys that I enjoy - not, for instance, really beautiful, or really powerful, or really weird. Really clever: it sounds like a put down, but it comes with a smile of pure admiration. What we're talking about is skill and the satisfaction in an art that really knows its stuff and makes it click. And since 1980, this stuff has been colour and its extreme relativity.

A pair of prints, Ra 2 and Silvered 2, are a sort of party piece here. Their ingredients are identical - each has the same number of stripes of the same range of colours, colours derived from Egyptian wall paintings. But the different ordering of the stripes is such as to demonstrate that relation: ordering is everything. Ra is hot, Silvered is cool; and what's more, Ra's whites are as hot as hot milk, while Silvered's whites are cold. What you find in this style generally, in big pictures such as Serenissima, is multiple change-ringing on limited palettes, adjacencies building up to one great colour chord.

Comparing abstract painting with music is a boring old trick (and the main point of it is negative, a way of saying to the sceptic: don't worry - abstraction may not seem to mean anything, but nor does music, and you don't mind that. But the analogy has a more positive purchase here, because Riley's work is quasi-notatable. She's using sets of discrete, distinct colour elements, which one can very easily think of as notes and scales involved in complex harmonies. But I admit that there's probably an element of visual association in the thought, the vertical stripes suggesting strings and staves. There may even be a lurking verbal pun on cords and chords.

And that's a problem, of course. At any rate, the artist herself is very down on this sort of resemblance finding. Indeed, she seems almost to wish that her pictures didn't have any "look" at all, or that the viewer didn't notice the colour-stripes and (later) colour diamonds of which they are made. There's no such thing as pure colour: it has to come in some shape and size. And if you're going to exercise very finely-tuned control, then you need constructive units that are, in effect, digital - separable, repeatable, combinable, gradable. But these qualities aren't interesting as such, just means to an end; an efficient way of creating different kinds of complex sensation.

Or so the argument would go, and fair enough: you can't forbid responses, but you can indicate what the most rewarding approach will be. The question then comes: what is the reward exactly? Are these pictures delightfully absorbing demonstrations of what can be done with their resources? Or are they, you know - nervously clears his throat - about something?

I think I'll simply leave this question in the air. Although Riley has often answered it in the affirmative, talking about nature and light and looking, I can never quite grasp what she's saying. And when I think I have grasped it, I then realise that that's because I've started to see the pictures in figurative-ish way, e.g. as dappled, bosky scenes, and that is absolutely not what is meant. (But actually, the most recent curvy work is undeniably bosky, in its shapes, rhythms and colours.)

Or perhaps it's really a question of Riley's development. She could go on introducing these small but radical gear changes every few years, give herself a new set of problems/potentials, work through them, hit the spot several times, shift again, and keep it up for centuries. No wonder she feels that abstract painting is still only at its early days (which nobody could say about the cinema, for example). As a matter of fact, artforms never die of literal exhaustion; always much earlier. But Riley's modus operandi has its eye on an infinitely elaborated repertoire. Her oeuvre implies a universe of painting, of which it would just be a tiny corner; rather sublime, in that way.

Bridget Riley, Works 1961-98, Abbot Hall Art Gallery, Kendal, Cumbria; until 31 January